STR #2609

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STR #2609

Application:FLTK Library
Status:5 - New
Priority:1 - Request for Enhancement, e.g. asking for a feature
Scope:3 - Applies to all machines and operating systems
Subsystem:Core Library
Summary:shape functions (fl_rectf etc.) support alpha
Created By:elaforge
Assigned To:Unassigned
Fix Version:Unassigned
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Name/Time/Date Text top right image
#1 elaforge
23:08 Apr 22, 2011
It would be nice if fl_rectf and friends could accept and RGBA color and draw a transparent shape.  I have emulated this by creating an Fl_RGB_Image and setting the alpha on all pixels, but it's ugly and inefficient.

This is complementary to STR 2583, which is for image level alpha support.
#2 eastern_strider
01:23 Jan 19, 2012
I also think this feature would be very useful. For instance, it can be used to select icons by dragging a transparent rectangle.

#3 matt
05:57 Jan 20, 2023
This is a bit by memory, but I will try to get that right. Most low-level graphics libraries do not support transparency, so we can't easily add this to FLTK. Also, FLTK tries to do minimal updates in graphics, so transparencies my multiply, leading to unexpected results. Example: set an antialiased font for text on a widget that has background without BOX, and drawing it multiple times will make the text look jaggy.

Images are different, because we have more control over drawing here.

If you draw into an Fl_GL_Window using FLTK calls, you can have transparency by setting color table entries with R, G, B, A.
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