Add support of RGB image and Pixmap drawing to class Fl_OpenGL_Graphics_Driver.

This allows to add RGB (and derived classes) or Pixmap images to widgets
layed over a GL scene.

src/drivers/OpenGL/Fl_OpenGL_Graphics_Driver.H

@@ -97,6 +97,9 @@ public:
   void text_extents(const char*, int n, int& dx, int& dy, int& w, int& h) FL_OVERRIDE;
   int height() FL_OVERRIDE;
   int descent() FL_OVERRIDE;
+  void cache_size(Fl_Image* img, int &width, int &height) override;
+  void draw_rgb(Fl_RGB_Image *img, int XP, int YP, int WP, int HP, int cx, int cy) override;
+  void draw_pixmap(Fl_Pixmap *img, int XP, int YP, int WP, int HP, int cx, int cy) override;
 };
 
 #endif // FL_OPENGL_GRAPHICS_DRIVER_H

src/drivers/OpenGL/Fl_OpenGL_Graphics_Driver_font.cxx

@@ -224,4 +224,114 @@ void Fl_OpenGL_Graphics_Driver::text_extents(const char *str, int n, int& dx, in
   Fl_Surface_Device::pop_current();
 }
 
+
+void Fl_OpenGL_Graphics_Driver::cache_size(Fl_Image* img, int &width, int &height) {
+  width *= pixels_per_unit_; // useful at least for Fl_SVG_Image's
+  height *= pixels_per_unit_;
+}
+
+
+#ifndef GL_TEXTURE_RECTANGLE_ARB
+#  define GL_TEXTURE_RECTANGLE_ARB 0x84F5
+#endif
+#ifndef GL_UNSIGNED_INT_8_8_8_8_REV
+#  define GL_UNSIGNED_INT_8_8_8_8_REV 0x8367
+#endif
+
+static GLuint compute_texture_rectangle(Fl_RGB_Image *rgb)
+{
+  GLuint texName;
+  glGenTextures(1, &texName);
+  // save GL parameters GL_UNPACK_ROW_LENGTH and GL_UNPACK_ALIGNMENT
+  GLint row_length, alignment;
+  glGetIntegerv(GL_UNPACK_ROW_LENGTH, &row_length);
+  glGetIntegerv(GL_UNPACK_ALIGNMENT, &alignment);
+  // put the bitmap in a texture
+  glPushAttrib(GL_TEXTURE_BIT);
+  glBindTexture (GL_TEXTURE_RECTANGLE_ARB, texName);
+  glTexParameteri(GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+  glPixelStorei(GL_UNPACK_ROW_LENGTH, (rgb->ld() ? rgb->ld() / rgb->d() : rgb->data_w()));
+  glPixelStorei(GL_UNPACK_ALIGNMENT, (rgb->d() == 3 ? 1 : 4));
+  glTexImage2D(GL_TEXTURE_RECTANGLE_ARB, 0, (rgb->d() == 3 ? GL_RGB : GL_RGBA8),
+               rgb->data_w(), rgb->data_h(), 0,
+               (rgb->d() == 3 ? GL_RGB : GL_RGBA),
+               (rgb->d() == 3 ? GL_UNSIGNED_BYTE : GL_UNSIGNED_INT_8_8_8_8_REV),
+               rgb->array);
+  glPopAttrib();
+  // restore saved GL parameters
+  glPixelStorei(GL_UNPACK_ROW_LENGTH, row_length);
+  glPixelStorei(GL_UNPACK_ALIGNMENT, alignment);
+  return texName;
+}
+
+
+void Fl_OpenGL_Graphics_Driver::draw_rgb(Fl_RGB_Image *img,
+                                         int XP, int YP, int WP, int HP, int cx, int cy) {
+  int X, Y, W, H;
+  // Don't draw an empty image. Gray-scale image drawing not implemented yet.
+  if (!img->d() || !img->array || img->d() < 3) {
+    Fl_Graphics_Driver::draw_empty(img, XP, YP);
+    return;
+  }
+  if (start_image(img, XP, YP, WP, HP, cx, cy, X, Y, W, H)) {
+    return;
+  }
+  Fl_RGB_Image *partial_rgb = NULL;
+  if (cx || cy || W < img->w() || H < img->h()) { // Partial image drawing.
+    int d = img->d();
+    int ld = d * img->data_w();
+    float sx = img->data_w() / float(img->w()), sy = img->data_h() / float(img->h());
+    cx *= sx; cy *= sy;
+    partial_rgb = new Fl_RGB_Image(img->array + cy * ld + cx * d, W * sx, H * sy, d, ld);
+    img = partial_rgb;
+  }
+  GLuint texName = compute_texture_rectangle(img);
+  // GL_TRANSFORM_BIT for GL_PROJECTION
+  // GL_TEXTURE_BIT for GL_TEXTURE_RECTANGLE_ARB
+  glPushAttrib(GL_TRANSFORM_BIT | GL_TEXTURE_BIT /*|GL_COLOR_BUFFER_BIT*/);
+  //setup matrices
+  glMatrixMode(GL_PROJECTION);
+  glPushMatrix();
+  glLoadIdentity();
+  glColor4ub(0xff, 0xff, 0xff, 0xff); // the color drawn through the texture seen as a kind of mask
+
+  float winw = Fl_Window::current()->as_gl_window()->pixel_w();
+  float winh = Fl_Window::current()->as_gl_window()->pixel_h();
+
+  float R = 2;
+  glScalef(R/winw, R/winh, 1.0f);
+  glTranslatef(-winw/R, -winh/R, 0.0f);
+  float s = Fl_Window::current()->as_gl_window()->pixels_per_unit();
+  int HH = s * H, WW = s * W;
+  float ox = s * X;
+  float oy = winh - s * Y;
+  glEnable(GL_TEXTURE_RECTANGLE_ARB);
+  glBindTexture(GL_TEXTURE_RECTANGLE_ARB, texName);
+  //write the texture on screen
+  glBegin(GL_QUADS);
+  glTexCoord2f(0.0f, 0.0f); // draw lower left in world coordinates
+  glVertex2f(ox, oy);
+  glTexCoord2f(0.0f, (GLfloat)img->data_h()); // draw upper left in world coordinates
+  glVertex2f(ox, oy - HH);
+  glTexCoord2f((GLfloat)img->data_w(), (GLfloat)img->data_h()); // draw upper right in world coordinates
+  glVertex2f(ox + WW, oy - HH);
+  glTexCoord2f((GLfloat)img->data_w(), 0.0f); // draw lower right in world coordinates
+  glVertex2f(ox + WW, oy);
+  glEnd();
+  glDeleteTextures(1, &texName);
+  color(color()); // reset current color
+  // reset original matrices
+  glMatrixMode(GL_PROJECTION);
+  glPopMatrix();
+  glPopAttrib(); // GL_TRANSFORM_BIT | GL_TEXTURE_BIT
+  if (partial_rgb) delete partial_rgb;
+}
+
+
+void Fl_OpenGL_Graphics_Driver::draw_pixmap(Fl_Pixmap *img,
+                                            int XP, int YP, int WP, int HP, int cx, int cy) {
+  Fl_RGB_Image rgb(img);
+  draw_rgb(&rgb, XP, YP, WP, HP, cx, cy);
+}
+
 #endif