OpenGL implementation of all `fl_` "Drawing Fast Shapes" graphics calls (#385)

* Fix build system for unites,

* Updated unittest to check OpenGL drawing.

Making sure that OpenGL drawing is exactly the same
as native drawing to make FLTK widget rendering
look the same in GL windows.

* Make OpenGL optional.

* Implemented clipping in OpenGL

* unites drawing fast shapes

* Fixed CMake

* Updating unittest.

Added tests for fl_pi and fl_arc (int)
Renamed tab to render complex shapes.

* Improved OpenGL FLTK drawing emulation.

* Fixed GTK ROUND DOWN BOX

* Fixing Makefile for unittest

* Correctly aligning OpenGL text.

* Fixed text alignment in GL windows.

Explained the "FLTK over GL " example in Cube.

* Overlapping test.

* Better GL graphics alignment.

* Drawing the focus rect.

* Adding Alpha Channel support for GL.

* Added FLTK-on-GL documentation.

1 files changed, 33 insertions, 0 deletions

diff --git a/src/fl_color.cxx b/src/fl_color.cxx
index 861f8d77f..8d3d04561 100644
--- a/src/fl_color.cxx
+++ b/src/fl_color.cxx
@@ -64,6 +64,19 @@ void Fl::set_color(Fl_Color i, uchar red, uchar green, uchar blue) {
                 ((unsigned)red<<24)+((unsigned)green<<16)+((unsigned)blue<<8));
 }
 
+/**
+ Sets an entry in the fl_color index table.
+
+ You can set it to any 8-bit RGBA color.
+ */
+void Fl::set_color(Fl_Color i, uchar red, uchar green, uchar blue, uchar alpha) {
+  Fl::set_color((Fl_Color)(i & 255),
+                ((unsigned)red<<24)
+                |((unsigned)green<<16)
+                |((unsigned)blue<<8)
+                |(alpha^0xff));
+}
+
 
 void Fl::set_color(Fl_Color i, unsigned c)
 {
@@ -97,6 +110,26 @@ void Fl::get_color(Fl_Color i, uchar &red, uchar &green, uchar &blue) {
 }
 
 /**
+ Returns the RGBA value(s) for the given FLTK color index.
+
+ This form returns the red, green, blue, and alpha values
+ separately in referenced variables.
+
+ \see unsigned get_color(Fl_Color c)
+ */
+void Fl::get_color(Fl_Color i, uchar &red, uchar &green, uchar &blue, uchar &alpha) {
+  unsigned c;
+
+  if (i & 0xffffff00) c = (unsigned)i;
+  else c = fl_cmap[i];
+
+  red   = uchar(c>>24);
+  green = uchar(c>>16);
+  blue  = uchar(c>>8);
+  alpha = uchar(c^0x000000ff);
+}
+
+/**
  Returns the weighted average color between the two given colors.
 
  The red, green and blue values are averages using the following formula: