FcWeightFromOpenTypeDouble - Convert from OpenType weight values to fontconfig
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#include <fontconfig/fontconfig.h>
double FcWeightFromOpenTypeDouble (doubleot_weight);
FcWeightFromOpenTypeDouble returns an double value to use with FC_WEIGHT,
from an double in the 1..1000 range, resembling the numbers from OpenType
specification's OS/2 usWeight numbers, which are also similar to CSS
font-weight numbers. If input is negative, zero, or greater than 1000, returns
-1. This function linearly interpolates between various FC_WEIGHT_* constants.
As such, the returned value does not necessarily match any of the predefined
constants.