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, 121 insertions, 0 deletions

diff --git a/test/unittest_complex_shapes.cxx b/test/unittest_complex_shapes.cxx
new file mode 100644
index 000000000..399243e4b
--- /dev/null
+++ b/test/unittest_complex_shapes.cxx
@@ -0,0 +1,121 @@
+//
+// Unit tests for the Fast Light Tool Kit (FLTK).
+//
+// Copyright 1998-2010 by Bill Spitzak and others.
+//
+// This library is free software. Distribution and use rights are outlined in
+// the file "COPYING" which should have been included with this file.  If this
+// file is missing or damaged, see the license at:
+//
+//     https://www.fltk.org/COPYING.php
+//
+// Please see the following page on how to report bugs and issues:
+//
+//     https://www.fltk.org/bugs.php
+//
+
+#include "unittests.h"
+
+#include <FL/Fl_Box.H>
+#include <FL/fl_draw.H>
+
+#if 0
+
+// TODO:
+void fl_push_matrix()
+void fl_pop_matrix()
+
+void fl_scale(double x,double y)
+void fl_scale(double x)
+void fl_translate(double x,double y)
+void fl_rotate(double d)
+void fl_mult_matrix(double a,double b,double c,double d,double x,double y)
+
+double fl_transform_x(double x, double y)
+double fl_transform_y(double x, double y)
+double fl_transform_dx(double x, double y)
+double fl_transform_dy(double x, double y)
+void fl_transformed_vertex(double xf, double yf)
+
+void fl_begin_points()
+void fl_end_points()
+
+void fl_begin_line()
+void fl_end_line()
+
+void fl_begin_loop()
+void fl_end_loop()
+
+void fl_begin_polygon()
+void fl_end_polygon()
+
+void fl_begin_complex_polygon()
+void fl_gap()
+void fl_end_complex_polygon()
+
+void fl_vertex(double x,double y)
+
+void fl_curve(double X0, double Y0, double X1, double Y1, double X2, double Y2, double X3, double Y3)
+
+void fl_arc(double x, double y, double r, double start, double end)
+void fl_circle(double x, double y, double r)
+
+
+#endif
+
+//
+//------- test Complex Shape drawing capabilities of this implementation ----------
+//
+class ComplexShapesTest : public Fl_Box {
+public:
+  static Fl_Widget *create() {
+    return new ComplexShapesTest(TESTAREA_X, TESTAREA_Y, TESTAREA_W, TESTAREA_H);
+  }
+  ComplexShapesTest(int x, int y, int w, int h) : Fl_Box(x, y, w, h) {
+    label("Testing complex shape drawing.\n\n"
+          "Complex Shapes in FLTK are rendered using floating point coordinates "
+          "which can be transformed through a matrix.");
+    align(FL_ALIGN_INSIDE|FL_ALIGN_BOTTOM|FL_ALIGN_LEFT|FL_ALIGN_WRAP);
+    box(FL_BORDER_BOX);
+  }
+  void draw() {
+    Fl_Box::draw();
+
+    int i, a = x()+10, b = y()+10; fl_color(FL_BLACK); fl_rect(a, b, 100, 100);
+    // testing fl_xyline(x, y, x1)
+    fl_color(FL_RED); fl_point(a+10, b+10); fl_point(a+20, b+10);
+    fl_color(FL_BLACK); fl_xyline(a+10, b+10, a+20);
+    // testing fl_xyline(x, y, x1, y2);
+    fl_color(FL_RED); fl_point(a+10, b+20); fl_point(a+20, b+20);
+    fl_point(a+20, b+30);
+    fl_color(FL_BLACK); fl_xyline(a+10, b+20, a+20, b+30);
+    // testing fl_xyline(x, y, x1, y2, x3);
+    fl_color(FL_RED); fl_point(a+10, b+40); fl_point(a+20, b+40);
+    fl_point(a+20, b+50); fl_point(a+30, b+50);
+    fl_color(FL_BLACK); fl_xyline(a+10, b+40, a+20, b+50, a+30);
+    //+++ add testing for the fl_yxline commands!
+    // testing fl_loop(x,y, x,y, x,y, x, y)
+    fl_color(FL_RED); fl_point(a+60, b+60); fl_point(a+90, b+60);
+    fl_point(a+60, b+90); fl_point(a+90, b+90);
+    fl_color(FL_BLACK);
+    fl_loop(a+60, b+60, a+90, b+60, a+90, b+90, a+60, b+90);
+
+    a = x()+120, b = y()+10; fl_color(FL_BLACK); fl_rect(a, b, 203, 203);
+    a += 101; b += 101;
+    fl_color(0xff888800);
+    for (i=-80; i<=80; i+=20) fl_line(a, b, a+i, b-100);
+    fl_color(0xff444400);
+    for (i=-80; i<=80; i+=20) fl_line(a, b, a+i, b+100);
+    fl_color(0x88ff8800);
+    for (i=-80; i<=80; i+=20) fl_line(a, b, a-100, b+i);
+    fl_color(0x44ff4400);
+    for (i=-80; i<=80; i+=20) fl_line(a, b, a+100, b+i);
+    fl_color(0x8888ff00);
+    fl_line(a, b, a-100, b-100);
+    fl_line(a, b, a+100, b-100);
+    fl_line(a, b, a+100, b+100);
+    fl_line(a, b, a-100, b+100);
+  }
+};
+
+//UnitTest lines(kTestComplexShapes, "Complex Shapes", ComplexShapesTest::create);