NAME

Prima::Widget - window management

SYNOPSIS

   # create a widget
   my $widget = Prima::Widget-> new(
       size    => [ 200, 200],
       color   => cl::Green,
       visible => 0,
       onPaint => sub {
          my ($self,$canvas) = @_;
          $canvas-> clear;
          $canvas-> text_out( "Hello world!", 10, 10);
       },
   );

   # manipulate the widget
   $widget-> origin( 10, 10);
   $widget-> show;

DESCRIPTION

Prima::Widget is a descendant of Prima::Component, a class, especially crafted to reflect and govern properties of a system-dependent window, such as its position, hierarchy, outlook etc. Prima::Widget is mapped into the screen space as a rectangular area, with distinct boundaries, pointer and sometimes cursor, and a user-selectable input focus.

USAGE

Prima::Widget class and its descendants are used widely throughout the toolkit, and, indeed provide almost all its user interaction and input-output. The notification system, explained in Prima::Object, is employed in Prima::Widget heavily, providing the programmer with unified access to the system-generated events, that occur when the user moves windows, clicks the mouse, types the keyboard, etc. Descendants of Prima::Widget use the internal, the direct method of overriding the notifications, whereas end programs tend to use the toolkit widgets equipped with anonymous subroutines ( see Prima::Object for the details).

The class functionality is much more extensive comparing to the other built-in classes, and therefore the explanations are grouped in several topics.

Creation and destruction

The widget creation syntax is the same as for the other Prima objects:

   Prima::Widget-> create(
      name => 'Widget',
      size => [ 20, 10],
      onMouseClick => sub { print "click\n"; },
      owner => $owner,
   );

In the real life, a widget must be almost always explicitly told about its owner. The owner object is either a Prima::Widget descendant, in which case the widget is drawn inside its inferior, or the application object, and in the latter case a widget becomes top-level. This is the reason why the "insert" syntax is much more often used, as it is more illustrative and is more convenient for creating several widgets in one call ( see Prima::Object ).

   $owner-> insert( 'Prima::Widget',
      name => 'Widget',
      size => [ 20, 10],
      onMouseClick => sub { print "click\n"; },
   );

These two examples produce identical results.

As a descendant of Prima::Component, Prima::Widget sends "Create" notification when created ( more precisely, after its init stage is finished. See Prima::Object for details). This notification is called and processed within "create()" call. In addition, another notification "Setup" is sent after the widget is created. This message is posted, so it is called within "create()" but processed in the application event loop. This means that the execution time of "Setup" is uncertain, as it is with all posted messages; its delivery time is system-dependent, so its use must be considered with care.

After a widget is created, it is usually asked to render its content, provided that the widget is visible. This request is delivered by means of "Paint" notification.

When the life time of a widget is over, its method "destroy()" is called, often implicitly. If a widget gets destroyed because its owner also does, it is guaranteed that the children widgets will be destroyed first, and the owner afterwards. In such situation, widget can operate with a limited functionality both on itself and its owners ( see Prima::Object, Creation section ).

Graphic content

A widget can use two different ways for representing its graphic content to the user. The first method is event-driven, when the "Paint" notification arrives, notifying the widget that it must re-paint itself. The second is the 'direct' method, when the widget generates graphic output unconditionally.

Event-driven rendering

A notification responsible for widget repainting is "Paint". It provides a single ( besides the widget itself ) parameter, an object, where the drawing is performed. In an event-driven call, it is always equals to the widget. However, if a custom mechanism should be used that directly calls, for example,

   $widget-> notify('Paint', $some_other_widget);

for whatever purpose, it is recommended ( not required, though ), to use this parameter, not the widget itself for painting and drawing calls.

The example of "Paint" callback is quite simple:

   Prima::Widget-> create(
       ...
       onPaint => sub {
          my ( $self, $canvas) = @_;
          $canvas-> clear;
          $canvas-> text_out("Clicked $self->{clicked} times", 10, 10);
       },
       onMouseClick => sub {
          $_[0]-> {clicked}++;
          $_[0]-> repaint;
       },
   );

The example uses several important features of the event-driven mechanism. First, no "begin_paint()"/"end_paint()" brackets are used within the callback. These are called implicitly. Second, when the custom refresh of the widget's graphic content is needed, no code like "notify(q(Paint))" is used - "repaint()" method is used instead. It must be noted, that the actual execution of "Paint" callbacks might or might not occur inside the "repaint()" call. This behavior is governed by the "::syncPaint" property. "repaint()" marks the whole widget's area to be refreshed, or invalidates the area. For the finer gradation of the area that should be repainted, "invalidate_rect()" and "validate_rect()" pair of functions is used. Thus,

  $x-> repaint()

code is a mere alias to

  $x-> invalidate_rect( 0, 0, $x-> size);

call. It must be realized, that the area, passed to "invalidate_rect()" only in its ideal ( but a quite often ) execution case will be pertained as a clipping rectangle when a widget executes its "Paint" notification. The user and system interactions can result in exposition of other parts of a widget ( like, moving windows over a widget ), and the resulting clipping rectangle can be different from the one that was passed to "invalidate_rect()". Moreover, the clipping rectangle can become empty as the result of these influences, and the notification will not be called at all.

Invalid rectangle is presented differently inside and outside the drawing mode. The first, returned by "::clipRect", employs inclusive-inclusive coordinates, whereas "invalidate_rect()", "validate_rect()" and "get_invalid_rect()" - inclusive-exclusive coordinates. The ideal case exemplifies the above said:

   $x-> onPaint( sub {
      my @c = $_[0]-> clipRect;
      print "clip rect:@c\n";
   });
   $x-> invalidate_rect( 10, 10, 20, 20);
   ...
   clip rect: 10 10 19 19

As noted above, "::clipRect" property is set to the clipping rectangle of the widget area that is needed to be refreshed, and an event handler code can take advantage of this information, increasing the efficiency of the painting procedure.

Further assignments of "::clipRect" property do not make possible over-painting on the screen area that lies outside the original clipping region. This is also valid for all paint operations, however since the original clipping rectangle is the full area of a canvas, this rule is implicit and unnecessary, because whatever large the clipping rectangle is, drawing and painting cannot be performed outside the physical boundaries of the canvas.

Direct rendering

The direct rendering, contrary to the event-driven, is initiated by the program, not by the system. If a programmer wishes to paint over a widget immediately, then "begin_paint()" is called, and, if successful, the part of the screen occupied by the widget is accessible to the drawing and painting routines.

This method is useful, for example, for graphic demonstration programs, that draw continuously without any input. Another field is the screen drawing, which is performed with Prima::Application class, that does not have "Paint" notification. Application's graphic canvas represents the whole screen, allowing over-drawing the graphic content of other programs.

The event-driven rendering method adds implicit "begin_paint()"/"end_paint()" brackets ( plus some system-dependent actions ) and is a convenience version of the direct rendering. Sometimes, however, the changes needed to be made to a widget's graphic context are so insignificant, so the direct rendering method is preferable, because of the cleaner and terser code. As an example might serve a simple progress bar, that draws a simple colored bar. The event-driven code would be ( in short, omitting many details ) as such:

   $bar = Widget-> create(
     width => 100,
     onPaint => sub {
        my ( $self, $canvas) = @_;
        $canvas-> color( cl::Blue);
        $canvas-> bar( 0, 0, $self-> {progress}, $self-> height);
        $canvas-> color( cl::Back);
        $canvas-> bar( $self-> {progress}, 0, $self-> size);
     },
   );
   ...
   $bar-> {progress} += 10;
   $bar-> repaint;
   # or, more efficiently, ( but clumsier )
   # $bar-> invalidate_rect( $bar->{progress}-10, 0,
   #                 $bar->{progress}, $bar-> height);

And the direct driven:

   $bar = Widget-> create( width => 100 );
   ...
   $bar-> begin_paint;
   $bar-> color( cl::Blue);
   $bar-> bar( $progress, 0, $progress + 10, $bar-> height);
   $bar-> end_paint;
   $progress += 10;

The pros and contras are obvious: the event-driven rendered widget correctly represents the status after an eventual repaint, for example when the user sweeps a window over the progress bar widget. The direct method cannot be that smart, but if the status bar is an insignificant part of the program, the trade-off of the functionality in favor to the code simplicity might be preferred.

Both methods can be effectively disabled using the paint locking mechanism. The "lock()" and "unlock()" methods can be called several times, stacking the requests. This feature is useful because many properties implicitly call "repaint()", and if several of these properties activate in a row, the unnecessary redrawing of the widget can be avoided. The drawback is that the last "unlock()" call triggers "repaint()" unconditionally.

Geometry

Basic properties

A widget always has its position and size determined, even if it is not visible on the screen. Prima::Widget provides several properties with overlapping functionality, that govern the geometry of a widget. The base properties are "::origin" and "::size", and the derived are "::left", "::bottom", "::right", "::top", "::width", "::height" and "::rect". "::origin" and "::size" operate with two integers, "::rect" with four, others with one integer value.

As the Prima toolkit coordinate space begins in the lower bottom corner, the combination of "::left" and "::bottom" is same as "::origin", and combination of "::left", "::bottom", "::right" and "::top" - same as "::rect".

When a widget is moved or resized, correspondingly two notifications occur: "Move" and "Size". The parameters to both are old and new position and size. The notifications occur irrespectable to whether the geometry change was issued by the program itself or by the user.

Implicit size regulations

Concerning the size of a widget, two additional two-integer properties exist, "::sizeMin" and "::sizeMax", that constrain the extension of a widget in their boundaries. The direct call that assigns values to the size properties that lie outside "::sizeMin" and "::sizeMax" boundaries, will fail - the widget extension will be adjusted to the boundary values, not to the specified ones.

Change to widget's position and size can occur not only by an explicit call to one of the geometry properties. The toolkit contains implicit rules, that can move and resize a widget corresponding to the flags, given to the "::growMode" property. The exact meaning of the "gm::XXX" flags is not given here ( see description to "::growMode" in API section ), but in short, it is possible with simple means to maintain widget's size and position regarding its owner, when the latter is resized. By default, and the default behavior corresponds to "::growMode" 0, widget does not change neither its size nor position when its owner is resized. It stays always in 'the left bottom corner'. When, for example, a widget is expected to stay in 'the right bottom corner', or 'the left top corner', the "gm::GrowLoX" and "gm::GrowLoY" values must be used, correspondingly. When a widget is expected to cover, for example, its owner's lower part and change its width in accord with the owner's, ( a horizontal scroll bar in an editor window is the example), the "gm::GrowHiX" value must be used.

When this implicit size change does occur, the "::sizeMin" and "::sizeMax" do take their part as well - they still do not allow the widget's size to exceed their boundaries. However, this algorithm has a problem, that is illustrated by the following setup. Imagine a widget with size-dependent "::growMode" ( with "gm::GrowHiX" or "gm::GrowHiY" bits set ) that must maintain certain relation between the owner's size and its own. If the implicit size change would depend on the actual widget size, derived as a result from the previous implicit size action, then its size (and probably position) will be incorrect after an attempt is made to change the widget's size to values outside the size boundaries.

Example: child widget has width 100, growMode set to "gm::GrowHiX" and sizeMin set to (95, 95). Its owner has width 200. If the owner widget changes gradually its width from 200 to 190 and then back, the following width table emerges:

                    Owner        Child
  Initial state      200           100
  Shrink             195   -5       95
  Shrink             190   -5       95 - as it can not be less than 95.
  Grow               195   +5      100
  Grow               200   +5      105

That effect would exist if the differential-size algorithm would be implemented, - the owner changes width by 5, and the child does the same. The situation is fixed by introducing the virtual size term. The "::size" property is derived from virtual size, and as "::size" cannot exceed the size boundaries, virtual size can. It can even accept the negative values. With this intermediate stage added, the correct picture occurs:

                    Owner        Child's       Child's
                                 virtual width  width
  Initial state      200           100           100
  Shrink             195   -5       95            95
  Shrink             190   -5       90            95
  Grow               195   +5       95            95
  Grow               200   +5      100           100

Geometry managers

The concept of geometry managers is imported from Tk, which in turn is a port of Tcl-Tk. The idea behind it is that a widget size and position is governed by one of the managers, which operate depending on the specific options given to the widget. The selection is operated by "::geometry" property, and is one of "gt::XXX" constants. The native ( and the default ) geometry manager is the described above grow-mode algorithm ( "gt::GrowMode" ). The currently implemented Tk managers are packer ( "gt::Pack" ) and placer ( "gt::Place"). Each has its own set of options and methods, and their manuals are provided separately in Prima::Widget::pack and Prima::Widget::place ( the manpages are also imported from Tk ).

Another concept that comes along with geometry managers is the 'geometry request size'. It is realized as a two-integer property "::geomSize", which reflects the size deduced by some intrinsic widget knowledge. The idea is that "::geomSize" it is merely a request to a geometry manager, whereas the latter changes "::size" accordingly. For example, a button might set its 'intrinsic' width in accord with the width of text string displayed in it. If the default width for such a button is not overridden, it is assigned with such a width. By default, under "gt::GrowMode" geometry manager, setting "::geomSize" ( and its two semi-alias properties "::geomWidth" and "::geomHeight" ) also changes the actual widget size.Moreover, when the size is passed to the Widget initialization code, "::size" properties are used to initialize "::geomSize". Such design minimizes the confusion between the two properties, and also minimizes the direct usage of "::geomSize", limiting it for selecting advisory size in widget internal code.

The geometry request size is useless under "gt::GrowMode" geometry manager, but Tk managers use it extensively.

Relative coordinates

Another geometry issue, or rather a programming technique must be mentioned - the relative coordinates. It is the well-known problem, when a dialog window, developed with one font looks garbled on another system with another font. The relative coordinates solve that problem; the solution is to use the "::designScale" two-integer property, the width and height of the font, that was used when the dialog window was designed. With this property supplied, the position and size supplied when a widget is actually created, are transformed in proportion between the designed and the actual font metrics.

The relative coordinates can be used only when passing the geometry properties values, and only before the creation stage, before a widget is created, because the scaling calculations perform in Prima::Widget::"profile_check_in()" method.

In order to employ the relative coordinates scheme, the owner ( or the dialog ) widget must set its "::designScale" to the font metrics and "::scaleChildren" property to 1. Widgets, created with owner that meets these requirements, participate in the relative coordinates scheme. If a widget must be excluded from the relative geometry applications, either the owner's property "::scaleChildren" must be set to 0, or the widget's "::designScale" must be set to "undef". As the default "::designScale" value is "undef", no default implicit relative geometry schemes are applied.

The "::designScale" property is auto-inherited; its value is copied to the children widgets, unless the explicit "::designScale" was given during the widget's creation. This is used when such a child widget serves as an owner for some other grand-children widgets; the inheritance scheme allows the grand- ( grand- etc ) children to participate in the relative geometry scheme.

Note: it is advised to test such applications with the Prima::Stress module, which assigns a random font as the default, so the testing phase does not involve tweaking of the system settings.

Z-order

In case when two widgets overlap, one of these is drawn in full, whereas the another only partly. Prima::Widget provides management of the Z-axis ordering, but since Z-ordering paradigm can hardly be fit into the properties scheme, the toolkit uses methods instead.

A widget can use four query methods: "first()", "last()", "next()", and "prev()". These return, correspondingly, the first and the last widgets in Z-order stack, and the direct neighbors of a widget ( $widget-> next-> prev always equals to the $widget itself, given that $widget-> next exists ).

The last widget is the topmost one, the one that is drawn fully. The first is the most obscured one, given that all the widgets overlap.

Z-order can also be changed at runtime ( but not during widget's creation). There are three methods: "bring_to_front()", that sets the widget last in the order, making it topmost, "send_to_back()", that does the reverse, and "insert_behind()", that sets a widget behind the another widget, passed as an argument.

Changes to Z-order trigger "ZOrderChanged" notification.

Parent-child relationship

By default, if a widget is a child to a widget or a window, it maintains two features: it is clipped by its owner's boundaries and is moved together as the owner widget moves, i.e. a child is inferior to its parent. However, a widget without a parent still does have a valid owner. Instead of implementing parent property, the "::clipOwner" property was devised. It is 1 by default, and if it is 1, then owner of a widget is its parent, at the same time. However, when it is 0, many things change. The widget is neither clipped nor moved together with its parent. The widget become parentless, or, more strictly speaking, the screen becomes its parent. Moreover, the widget's origin offset is calculated then not from the owner's coordinates but from the screen, and mouse events in the widget do not transgress implicitly to the owner's top-level window eventual decorations.

The same results are produced if a widget is inserted in the application object, which does not have screen visualization. A widget that belongs to the application object, can not reset its "::clipOwner" value to 1.

The "::clipOwner" property opens a possibility for the toolkit widgets to live inside other programs' windows. If the "::parentHandle" is changed from its default "undef" value to a valid system window handle, the widget becomes child to this window, which can belong to any application residing on the same display. This option is dangerous, however: normally widgets never get destroyed by no reason. A top-level window is never destroyed before its "Close" notification grants the destruction. The case with "::parentHandle" is special, because a widget, inserted into an alien application, must be prepared to be destroyed at any moment. It is recommended to use prior knowledge about such the application, and, even better, use one or another inter-process communication scheme to interact with it.

A widget does not need to undertake anything special to become an 'owner'. Any widget, that was set in "::owner" property on any other widget, becomes an owner automatically. Its "get_widgets()" method returns non-empty widget list. "get_widgets()" serves same purpose as Prima::Component::"get_components()", but returns only Prima::Widget descendants.

A widget can change its owner at any moment. The "::owner" property is both readable and writable, and if a widget is visible during the owner change, it is immediately appeared under different coordinates and different clipping condition after the property change, given that its "::clipOwner" is set to 1.

Visibility

A widget is created visible by default. Visible means that it is shown on the screen if it is not shadowed by other widgets or windows. The visibility is governed by the "::visible" property, and its two convenience aliases, "show()" and "hide()".

When a widget is invisible, its geometry is not discarded; the widget pertains its position and size, and is subject to all previously discussed implicit sizing issues. When change to "::visible" property is made, the screen is not updated immediately, but in the next event loop invocation, because uncovering of the underlying area of a hidden widget, and repainting of a new-shown widget both depend onto the event-driven rendering functionality. If the graphic content must be updated, "update_view()" must be called, but there's a problem. It is obvious that if a widget is shown, the only content to be updated is its own. When a widget becomes hidden, it may uncover more than one widget, depending on the geometry, so it is unclear what widgets must be updated. For the practical reasons, it is enough to get one event loop passed, by calling "yield()" method of the $::application object. The other notifications may pass here as well, however.

There are other kinds of visibility. A widget might be visible, but one of its owners might not. Or, a widget and its owners might be visible, but they might be over-shadowed by the other windows. These conditions are returned by "showing()" and "exposed()" functions, correspondinly. These return boolean values corresponding to the condition described. So, if a widget is 'exposed', it is 'showing' and 'visible'; "exposed()" returns always 0 if a widget is either not 'showing' or not 'visible'. If a widget is 'showing', then it is always 'visible'. "showing()" returns always 0 if a widget is invisible.

Visibility changes trigger "Hide" and "Show" notifications.

Focus

One of the key points of any GUI is that only one window at a time can possess a focus. The widget is focused, if the user's keyboard input is directed to it. The toolkit adds another layer in the focusing scheme, as often window managers do, highlighting the decorations of a top-level window over a window with the input focus.

Prima::Widget property "::focused" governs the focused state of a widget. It is sometimes too powerful to be used. Its more often substitutes, "::selected" and "::current" properties provide more respect to widget hierarchy.

"::selected" property sets focus to a widget if it is allowed to be focused, by the usage of the "::selectable" property. With this granted, the focus is passed to the widget or to the one of its ( grand-) children. So to say, when 'selecting' a window with a text field by clicking on a window, one does not expect the window itself to be focused, but the text field. To achieve this goal and reduce unnecessary coding, the "::current" property is introduced. With all equal conditions, a widget that is 'current' gets precedence in getting selected over widgets that are not 'current'.

De-selecting, in its turn, leaves the system in such a state when no window has input focus. There are two convenience shortcuts "select()" and "deselect()" defined, aliased to selected(1) and selected(0), correspondingly.

As within the GUI space, there can be only one 'focused' widget, so within the single widget space, there can be only one 'current' widget. A widget can be marked as a current by calling "::current" ( or, identically, "::currentWidget" on the owner widget ). The reassignments are performed automatically when a widget is focused. The reverse is also true: if a widget is explicitly marked as 'current', and belongs to the widget tree with the focus in one of its widgets, then the focus passed to the 'current' widget, or down to its hierarchy if it is not selectable.

These relations between current widget pointer and focus allow the toolkit easily implement the focusing hierarchy. The focused widget is always on the top of the chain of its owner widgets, each of whose is a 'current' widget. If, for example, a window that contains a widget that contains a focused button, become un-focused, and then user selects the window again, then the button will become focused automatically.

Changes to focus produce "Enter" and "Leave" notifications.

Below discussed mouse- and keyboard- driven focusing schemes. Note that all of these work via "::selected", and do not focus the widgets with "::selectable" property set to 0.

Mouse-aided focusing

Typically, when the user clicks the left mouse button on a widget, the latter becomes focused. One can note that not all widgets become focused after the mouse click - scroll bars are the examples. Another kind of behavior is the described above window with the text field - clicking mouse on a window focuses a text field.

Prima::Widget has the "::selectingButtons" property, a combination of mb::XXX ( mouse buttons ) flags. If the bits corresponding to the buttons are set, then click of this button will automatically call ::selected(1) ( not ::focused(1) ).

Another boolean property, "::firstClick" determines the behavior when the mouse button action is up to focus a widget, but the widget's top-level window is not active. The default value of "::firstClick" is 1, but if set otherwise, the user must click twice to a widget to get it focused. The property does not influence anything if the top-level window was already active when the click event occured.

Due to different GUI designs, it is hardly possibly to force selection of one top-level window when the click was on the another. The window manager or the OS can interfere, although this does not always happen, and produces different results on different platforms. Since the primary goal of the toolkit is portability, such functionality must be considered with care. Moreover, when the user selects a window by clicking not on the toolkit-created widgets, but on the top-level window decorations, it is not possible to discern the case from any other kind of focusing.

Keyboard focusing

The native way to navigate between the toolkit widgets are tab- and arrow- navigation. The tab ( and its reverse, shift-tab ) key combinations circulate the focus between the widgets in same top-level group ( but not inside the same owner widget group ). The arrow keys, if the focused widget is not interested in these keystrokes, move the focus in the specified direction, if it is possible. The methods that provide the navigations are available and called "next_tab()" and "next_positional()", correspondingly ( see API for the details).

When "next_positional()" operates with the geometry of the widgets, "next_tab()" uses the "::tabStop" and "::tabOrder" properties. "::tabStop", the boolean property, set to 1 by default, tells if a widget is willing to participate in tab-aided focus circulation. If it doesn't, "next_tab()" never uses it in its iterations. "::tabOrder" value is an integer, unique within the sibling widgets ( sharing same owner ) list, and is used as simple tag when the next tab-focus candidate is picked up. The default "::tabOrder" value is -1, which changes automatically after widget creation to a unique value.

User input

The toolkit responds to the two basic means of the user input - the keyboard and the mouse. Below described three aspects of the input handling - the event-driven, the polling and the simulated input issues. The event-driven input is the more or less natural way of communicating with the user, so when the user presses the key or moves the mouse, a system event occurs and triggers the notification in one or more widgets. Polling methods provide the immediate state of the input devices; the polling is rarely employed, primarily because of its limited usability, and because the information it provides is passed to the notification callbacks anyway. The simulated input is little more than "notify()" call with specifically crafted parameters. It interacts with the system, so the emulation can gain the higher level of similarity to the user actions. The simulated input functions allow the notifications to be called right away, or post it, delaying the notification until the next event loop invocation.

Keyboard

Event-driven

Keyboard input generates several notifications, where the most important are "KeyDown" and "KeyUp". Both have almost the same list of parameters ( see API ), that contain the key code, its modifiers ( if any ) that were pressed and an eventual character code. The algorithms that extract the meaning of the key, for example, discretion between character and functional keys etc are not described here. The reader is advised to look at Prima::KeySelector module, which provides convenience functions for keyboard input values transformations, and to the Prima::Edit and Prima::InputLine modules, the classes that use extensively the keyboard input. But in short, the key code is one of the "kb::XXX" ( like, kb::F10, kb::Esc ) constants, and the modifier value is a combination of the "km::XXX" ( km::Ctrl, km::Shift) constants. The notable exception is kb::None value, which hints that the character code is of value. Some other "kb::XXX"-marked keys have the character code as well, and it is up to a programmer how to treat these combinations. It is advised, however, to look at the key code first, and then to the character code.

"KeyDown" event has also the repeat integer parameter, that shows the repetitive count how many times the key was pressed. Usually it is 1, but if a widget was not able to get its portion of events between the key presses, its value can be higher. If a code doesn't check for this parameter, some keyboard input may be lost. If the code will be too much complicated by introducing the repeat-value, one may consider setting the "::briefKeys" property to 0. "::briefKeys", the boolean property, is 1 by default. If set to 0, it guarantees that the repeat value will always be 1, but with the price of certain under-optimization. If the core "KeyDown" processing code sees repeat value greater than 1, it simply calls the notification again.

Along with these two notifications, the "TranslateAccel" event is generated after "KeyDown", if the focused widget is not interested in the key event. Its usage covers the needs of the other widgets that are willing to read the user input, even being out of focus. A notable example can be a button with a hot key, that reacts on the key press when the focus is elsewhere within its top-level window. "TranslateAccel" has same parameters as "KeyDown", except the REPEAT parameter.

Such out-of-focus input is also used with built-in menu keys translations. If a descendant of Prima::AbstractMenu is in the reach of the widget tree hierarchy, then it is checked whether it contains some hot keys that match the user input. See Prima::Menu for the details. In particular, Prima::Widget has "::accelTable" property, a mere slot for an object that contains a table of hot keys mappings to custom subroutines.

Polling

The polling function for the keyboard is limited to the modifier keys only. "get_shift_state()" method returns the press state of the modifier keys, a combination of "km::XXX" constants.

Simulated input

There are two methods, corresponding to the major notifications - "key_up()" and "key_down()", that accept the same parameters as the "KeyUp" and "KeyDown" notifications do, plus the POST boolean flag. See "API" for details.

These methods are convenience wrappers for "key_event()" method, which is never used directly.

Mouse

Event-driven

Mouse notifications are send in response when the user moves the mouse, or presses and releases mouse buttons. The notifications are logically grouped in two sets, the first contains "MouseDown", "MouseUp", "MouseClick", and "MouseWheel", and the second - "MouseMove", "MouseEnter", end "MouseLeave".

The first set deals with button actions. Pressing, de-pressing, clicking ( and double-clicking ), the turn of mouse wheel correspond to the four notifications. The notifications are sent together with the mouse pointer coordinates, the button that was touched, and the eventual modifier keys that were pressed. In addition, "MouseClick" provides the boolean flag if the click was single or double, and "MouseWheel" the wheel turn amount. These notifications occur when the mouse event occurs within the geometrical bounds of a widget, with one notable exception, when a widget is in capture mode. If the "::capture" is set to 1, then these events are sent to the widget even if the mouse pointer is outside, and not sent to the widgets and windows that reside under the pointer.

The second set deals with the pointer movements. When the pointer passes over a widget, it receives first "MouseEnter", then series of "MouseMove", and finally "MouseLeave". "MouseMove" and "MouseEnter" notifications provide X,Y-coordinates and modificator keys; "MouseLeave" passes no parameters.

Polling

The mouse input polling procedures are "get_mouse_state()" method, that returns combination of "mb::XXX" constants, and the "::pointerPos" two-integer property that reports the current position of the mouse pointer.

Simulated input

There are five methods, corresponding to the mouse events - "mouse_up()", "mouse_down()", "mouse_click()", "mouse_wheel()" and "mouse_move()", that accept the same parameters as their event counterparts do, plus the POST boolean flag. See "API" for details.

These methods are convenience wrappers for "mouse_event()" method, which is never used directly.

Drag and drop

Widgets can participate in full drag and drop sessions with other applications and itself, with very few restrictions. See below how to use this functionality.

Data exchange

Prima defines a special clipboard object that serves as an exchange point whenever data is to be either sent or received. In order to either offer to, or choose from, many formats of another DND client, use that clipboard to operate with standard open/fetch/store/close methods (see more at Prima::Clipboard).

The clipboard can be accessed at any time by calling " $::application-" get_dnd_clipboard >, however during handling of dropping events it will stay read-only.

To successfully exchange data with other applictions, one may investigate results of "$clipboard-> get_formats(1)" to see what types of data the selected application can exchange. With a high probability many programs can exchange text and image in a system-dependent format, however it is also common to see applications to exchange data in format names that match their MIME description. For example Prima supports image formats like "image/bmp" out of the box, and "text/plain" on X11, that are selected automatically when operating with pseudo-formats "Text" or "Image". Other MIME formats like f.ex. "text/html" are not known to Prima, but can be exchanged quite easily; one needs to register that format first using "Clipbpard::register_format", once, and then it is ready for exachange.

Dragging

To initiate the drag, first fill the DND clipboard with data to be exchanged, using one or more formats, then call either "start_dnd". Alternatively, call "begin_drag", a wrapper method that can set up clipboard data itself. See their documentation for more details.

During the dragging, the sender will receive "DragQuery" and "DragResponse" events, in order to decide whether the drag session must continue or stop depending on the user input, and reflect that back to the user. Traditionally, mouse cursors are changed to show whether an application will receive a drop, and if yes, what action (copy, move, or link) it will participate in. Prima will try its best to either use system cursors, or synthesise ones that are informative enough; if that is not sufficient, one may present own cursor schema (see f.ex how "begin_drag" is implemented).

Dropping

To register a widget as a drop target, set its "dndAware" property to either 1, to mark that it will answer to all formats, or to a string, in which case drop events will only be delivered if the DND clipboard contains a format with that string.

Thereafter, when the user will initiate a DND session and will move mouse pointer over the widget, it will receive a "DragBegin" event, then series of "DragOver" events, and finally a "DragEnd" event with a flag telling whether the user chose to drop the data or cancel the session.

The "DragOver" and "DragEnd" callbacks have a chance to either allow or deny data, and select an action (if there are more than one allowed by the other application) to proceed with. To do so, set appropriate values to "{allow}" and "{action}" in the last hashref parameter that is sent to these event handlers. Additionally, "DragOver" can set a "{pad}" rectangle that will cache the last answer and will tell the system not to send repeated event with same input while the mouse pointer stays in the same rectangle.

Portability

X11 and Win32 are rather identical in how they are handing a DND session from the user's perspective. The only difference that is significant to Prima here is whether the sender or the receiver is responsible to select an action for available list of actions, when the user presses modifier keys, like CTRL or SHIFT.

On X11, it is the sender that contols that aspect, and tells the receiver what action at any given moment the user chose, by responding to a "DragQuery" event. On Win32, it is the receiver that selects an action from the list on each "DragOver" event, depending on modifier keys pressed by the user; Windows recommends to adhere to the standard scheme where CTRL mark "dnd::Move" action, and SHIFT the "dnd::Link", but that is up to the receiver.

Thus, to write an effective portable program, assume that your program may control the actions both as sender and as a receiver; Prima system-dependent code will make sure that there will be no ambiguities on the input. F.ex. a sender on Win32 will never be presented with a combination of several "dnd::" constants inside a "DragQuery" event, and a X11 receiver will similarly never be presented with such combination inside "DragOver". However, a portable program must be prepared to select and return a DND action in either callback.

Additionally, a X11 non-Prima receiver, when presented with a multiple choice of actions, may ask the user what action to select, or cancel the session altogether. This is okay and is expected by the user.

Color schemes

Prima::Drawable deals only with such color values, that can be unambiguously decomposed to their red, green and blue components. Prima::Widget extends the range of the values acceptable by its color properties, introducing the color schemes. The color can be set indirectly, without prior knowledge of what is its RGB value. There are several constants defined in "cl::" name space, that correspond to the default values of different color properties of a widget.

Prima::Widget revises the usage of "::color" and "::backColor", the properties inherited from Prima::Drawable. Their values are widget's 'foreground' and 'background' colors, in addition to their function as template values. Moreover, their dynamic change induces the repainting of a widget, and they can be inherited from the owner. The inheritance is governed by properties "::ownerColor" and "::ownerBackColor". While these are true, changes to owner "::color" or "::backColor" copied automatically to a widget. Once the widget's "::color" or "::backColor" are explicitly set, the owner link breaks automatically by setting "::ownerColor" or "::ownerBackColor" to 0.

In addition to these two color properties, Prima::Widget introduces six others. These are "::disabledColor", "::disabledBackColor", "::hiliteColor", "::hiliteBackColor", "::light3DColor", and "::dark3DColor". The 'disabled' color pair contains the values that are expected to be used as foreground and background when a widget is in the disabled state ( see API, "::enabled" property ). The 'hilite' values serve as the colors for representation of selection inside a widget. Selection may be of any kind, and some widgets do not provide any. But for those that do, the 'hilite' color values provide distinct alternative colors. Examples are selections in the text widgets, or in the list boxes. The last pair, "::light3DColor" and "::dark3DColor" is used for drawing 3D-looking outlines of a widget. The purpose of all these properties is the adequate usage of the color settings, selected by the user using system-specific tools, so the program written with the toolkit would look not such different, and more or less conformant to the user's color preferences.

The additional "cl::" constants, mentioned above, represent these eight color properties. These named correspondingly, cl::NormalText, cl::Normal, cl::HiliteText, cl::Hilite, cl::DisabledText, cl::Disabled, cl::Light3DColor and cl::Dark3DColor. cl::NormalText is alias to cl::Fore, and cl::Normal - to cl::Back. Another constant set, "ci::" can be used with the "::colorIndex" property, a multiplexer for all eight color properties. "ci::" constants mimic their non-RGB "cl::" counterparts, so the call "hiliteBackColor(cl::Red)" is equal to "colorIndex(ci::Hilite, cl::Red)".

Mapping from these constants to the RGB color representation is used with "map_color()" method. These "cl::" constants alone are sufficient for acquiring the default values, but the toolkit provides wider functionality than this. The "cl::" constants can be combined with the "wc::" constants, that represent standard widget class. The widget class is implicitly used when single "cl::" constant is used; its value is read from the "::widgetClass" property, unless one of "wc::" constants is combined with the non-RGB "cl::" value. "wc::" constants are described in "API"; their usage can make call of, for example, "backColor( cl::Back)" on a button and on an input line result in different colors, because the "cl::Back" is translated in the first case into "cl::Back|wc::Button", and in another - "cl::Back|wc::InputLine".

Dynamic change of the color properties result in the "ColorChanged" notification.

Fonts

Prima::Widget does not change the handling of fonts - the font selection inside and outside "begin_paint()"/"end_paint()" is not different at all. A matter of difference is how does Prima::Widget select the default font.

First, if the "::ownerFont" property is set to 1, then font of the owner is copied to the widget, and is maintained all the time while the property is true. If it is not, the default font values read from the system.

The default font metrics for a widget returned by "get_default_font()" method, that often deals with system-dependent and user-selected preferences ( see "Additional resources" ). Because a widget can host an eventual Prima::Popup object, it contains "get_default_popup_font()" method, that returns the default font for the popup objects. The dynamic popup font settings governed, naturally, by the "::popupFont" property. Prima::Window extends the functionality to "get_default_menu_font()" and the "::menuFont" property.

Dynamic change of the font property results in the "FontChanged" notification.

Additional resources

The resources, operated via Prima::Widget class but not that strictly bound to the widget concept, are gathered in this section. The section includes overview of pointer, cursor, hint, menu objects and user-specified resources.

Markup text

"Prima::Drawable::Markup" provides text-like objects that can include font and color change, and has a primitive image support. Since text methods of "Prima::Drawable" such as "text_out", "get_text_width" etc can detect if a text passed is actually a blessed object, and make a corresponding call on it, the markup objects can be used transparently when rich text is needed, simply by passing them to "text" and "hint" properties.

There are two ways to construct a markup object: either directly:

   Prima::Drawable::Markup->new( ... )

or using an imported method "M",

   use Prima::Drawable::Markup q(M);
   M '...';

where results of both can be directly set to almost any textual property throughout the whole toolkit, provided that the classes are not peeking inside the object but only calling drawing methods on them.

In addition to that, "Prima::Widget" and its descendants recognize a third syntax

  Widget->new( text => \ 'markup' )

treating a scalar reference to a text string as a sign that this is actually the text to be compiled into a markup object.

Pointer

The mouse pointer is the shared resource, that can change its visual representation when it hovers over different kinds of widgets. It is usually a good practice for a text field, for example, set the pointer icon to a jagged vertical line, or indicate a moving window with a cross-arrowed pointer.

A widget can select either one of the predefined system pointers, mapped by the "cr::XXX" constant set, or supply its own pointer icon of an arbitrary size and color depth.

NB: Not all systems allow the colored pointer icons. System value under sv::ColorPointer index containing a boolean value, whether the colored icons are allowed or not. Also, the pointer icon size may have a limit: check if sv::FixedPointerSize is non-zero, in which case the pointer size will be reduced to the system limits.

In general, the "::pointer" property is enough for these actions. It discerns whether it has an icon or a constant passed, and sets the appropriate properties. These properties are also accessible separately, although their usage is not encouraged, primarily because of the tangled relationship between them. These properties are: "::pointerType", "::pointerIcon", and "::pointerHotSpot". See their details in the "API" sections.

Another property, which is present only in Prima::Application name space is called "::pointerVisible", and governs the visibility of the pointer - but for all widget instances at once.

Cursor

The cursor is a blinking rectangular area, indicating the availability of the input focus in a widget. There can be only one active cursor per a GUI space, or none at all. Prima::Widget provides several cursor properties: "::cursorVisible", "::cursorPos", and "::cursorSize". There are also two methods, "show_cursor()" and "hide_cursor()", which are not the convenience shortcuts but the functions accounting the cursor hide count. If "hide_cursor()" was called three times, then "show_cursor()" must be called three times as well for the cursor to become visible.

Hint

"::hint" is a text string, that usually describes the widget's purpose to the user in a brief manner. If the mouse pointer is hovered over the widget longer than some timeout ( see Prima::Application::hintPause ), then a label appears with the hint text, until the pointer is drawn away. The hint behavior is governed by Prima::Application, but a widget can do two additional things about hint: it can enable and disable it by calling "::showHint" property, and it can inherit the owner's "::hint" and "::showHint" properties using "::ownerHint" and "::ownerShowHint" properties. If, for example, "::ownerHint" is set to 1, then "::hint" value is automatically copied from the widget's owner, when it changes. If, however, the widget's "::hint" or "::showHint" are explicitly set, the owner link breaks automatically by setting "::ownerHint" or "::ownerShowHint" to 0.

The widget can also operate the "::hintVisible" property, that shows or hides the hint label immediately, if the mouse pointer is inside the widget's boundaries.

Menu objects

The default functionality of Prima::Widget coexists with two kinds of the Prima::AbstractMenu descendants - Prima::AccelTable and Prima::Popup ( Prima::Window is also equipped with Prima::Menu reference). The "::items" property of these objects are accessible through "::accelItems" and "::popupItems", whereas the objects themselves - through "::accelTable" and "::popup", correspondingly. As mentioned in "User input", these objects hook the user keyboard input and call the programmer-defined callback subroutine if the key stroke equals to one of their table values. As for "::accelTable", its function ends here. "::popup" provides access to a context pop-up menu, which can be invoked by either right-clicking or pressing a system-dependent key combination. As a little customization, the "::popupColorIndex" and "::popupFont" properties are introduced. ( "::popupColorIndex" is multiplexed to "::popupColor", "::popupHiliteColor", "::popupHiliteBackColor", etc etc properties exactly like the "::colorIndex" property ).

The font and color of a menu object might not always be writable (Win32).

The Prima::Window class provides equivalent methods for the menu bar, introducing "::menu", "::menuItems", "::menuColorIndex" ( with multiplexing ) and "::menuFont" properties.

User-specified resources

It is considered a good idea to incorporate the user preferences into the toolkit look-and-feel. Prima::Widget relies to the system-specific code that tries to map these preferences as close as possible to the toolkit paradigm.

Unix version employs XRDB ( X resource database ), which is the natural way for the user to tell the preferences with fine granularity. Win32 reads the setting that the user has to set interactively, using system tools. Nevertheless, the toolkit can not emulate all user settings that are available on the supported platforms; it rather takes a 'least common denominator', which is colors and fonts. "fetch_resource()" method is capable of returning any of such settings, provided it's format is font, color or a string. The method is rarely called directly.

The appealing idea of making every widget property adjustable via the user-specified resources is not implemented in full. It can be accomplished up to a certain degree using "fetch_resource()" existing functionality, but it is believed that calling up the method for the every property for the every widget created is prohibitively expensive.

API

Properties

accelItems [ ITEM_LIST ]

Manages items of a Prima::AccelTable object associated with a widget. The ITEM_LIST format is same as "Prima::AbstractMenu::items" and is described in Prima::Menu.

Methods

begin_drag [ DATA | %OPTIONS ]

Wrapper over "dnd_start" that takes care of some DND session aspects other than the default system's. All input is contained in %OPTIONS hash, except for the case of a single-parameter call, in which case it is equivalent to "text => DATA" when "DATA" is a scalar, and to "image => DATA" when "DATA" is a reference.

Returns -1 if a session cannot start, "dnd::None" if it was cancelled by the user, or any other "dnd::" constant when the DND receiver has selected and successfully performed that action. For example, after a call to "dnd_start" returning "dnd::Move" (depending on a context), the caller may remove the data the user selected to move ("Prima::InputLine" and "Prima::Edit" do exactly this).

In "wantarray" context also returns the widget that accepted the drop, if that was a Prima widget. Check this before handling "dnd::Move" actions that require data to be deleted on the source, to not occasionally delete the freshly transferred data. The method uses a precaution for this scenario and by default won't let the widget to be both a sender and a receiver though ( see "self_aware" below ).

The following input is recognized:

actions INTEGER = dnd::Copy: Combination of "dnd::" constants, to tell a DND receiver whether copying, moving, and/or linking of the data is allowed. The method fails on the invalid "actions" input.
format FORMAT, data INPUT: If set, the clipboard will be assigned to contain a single entry of "INPUT" of the "FORMAT" format, where format is either one of the standard "Text" or "Image", or one of the format registered by "Clipboard::register_format".
If not set, the caller needs to fill the clipboard in advance, f.ex. to offer data in more than one format.
image INPUT: Shortcut for " format =" 'Image', data => $INPUT, preview => $INPUT >
preview INPUT: If set, mouse pointers sending feedback to the user will be equipped with either text or image (depending on whether "INPUT" is a scalar or an image reference).
self_aware BOOLEAN = 1: If unset the widget's "dndAware" will be temporarily set to 0, to exclude a possibility of an operation that may end in sending data to itself.
text INPUT: Shortcut for " format =" 'Text', data => $INPUT, preview => $INPUT >
track INTEGER = 5: When set, waits with starting the DND process until the user moves the pointer from the starting point further than "track" pixels, which makes sense if the method to be called directly from a "MouseDown" event handler.
If the drag did not happen because the user released the button or otherwise marked that this is not a drag, -1 is returned. In that case, the caller should continue to handle "MouseDown" event as if no drag sesssion was ever started.

bring_to_front

Sends a widget on top of all other siblings widgets

See also: "insert_behind", "send_to_back", "ZOrderChanged" ,"first", "next", "prev", "last"

can_close

Sends "Close" message, and returns its boolean exit state.

Get-methods

get_default_font: Returns the default font for a Prima::Widget class.
See also: "font"
get_default_popup_font: Returns the default font for a Prima::Popup class.
See also: "font"
get_invalid_rect: Returns the result of successive calls "invalidate_rect()", "validate_rect()" and "repaint()", as a rectangular area ( four integers ) that cover all invalid regions in a widget. If none found, (0,0,0,0) is returned.
See also: "validate_rect", "invalidate_rect", "repaint", "Paint", "syncPaint", "update_view"
get_handle: Returns a system handle for a widget
See also: "get_parent_handle", "Window::get_client_handle"
get_locked: Returns 1 if a widget is in "lock()" - initiated repaint-blocked state.
See also: "lock", "unlock"
get_mouse_state: Returns a combination of "mb::XXX" constants, reflecting the currently pressed mouse buttons.
See also: "pointerPos", "get_shift_state"
get_parent: Returns the owner widget that clips the widget boundaries, or application object if a widget is top-level.
See also: "clipOwner"
get_parent_handle: Returns a system handle for a parent of a widget, a window that belongs to another program. Returns 0 if the widget's owner and parent are in the same application and process space.
See also: "get_handle", "clipOwner"
get_pointer_size: Returns two integers, width and height of a icon, that the system accepts as valid for a pointer. If the icon is supplied that is more or less than these values, it is truncated or padded with transparency bits, but is not stretched. Can be called with class syntax.
get_shift_state: Returns a combination of "km::XXX" constants, reflecting the currently pressed keyboard modificator buttons.
See also: "get_shift_state"
get_virtual_size: Returns virtual width and height of a widget. See "Geometry", Implicit size regulations.
See also: "width", "height", "size" "growMode", "Move", "Size", "sizeMax", "sizeMin"
get_widgets: Returns list of children widgets.

Events

Change

Generic notification, used for Prima::Widget descendants; Prima::Widget itself neither calls not uses the event. Designed to be called when an arbitrary major state of a widget is changed.

Click

Generic notification, used for Prima::Widget descendants; Prima::Widget itself neither calls not uses the event. Designed to be called when an arbitrary major action for a widget is called.

Close

Triggered by "can_close()" and "close()" functions. If the event flag is cleared during execution, these functions fail.

AUTHOR

Dmitry Karasik, <dmitry@karasik.eu.org>.