Shadow Map Sample

core/cross/gl/renderer_gl.cc

 /*
  * Copyright 2009, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 1549 matching lines @@
                                       height));
 }
 
 // Saves a png screenshot 'file_name.png'.
 // Returns true on success and false on failure.
 bool RendererGL::SaveScreen(const String& file_name) {
 #ifdef TESTING
   MakeCurrentLazy();
   Bitmap::Ref bitmap = Bitmap::Ref(new Bitmap(service_locator()));
   bitmap->Allocate(Texture::ARGB8, width(), height(), 1, false);
+  
+  // Note: glReadPixels caputres the alpha component of the frame buffer as well
+  // as the color components, the graphics pipeline usually ignores the alpha
+  // channel when drawing to the screen, so unless the alpha is 1, the png image
+  // generated might exhibit suprise translucency.
   ::glReadPixels(0, 0, width(), height(), GL_BGRA, GL_UNSIGNED_BYTE,
                  bitmap->image_data());
   bool result = bitmap->SaveToPNGFile((file_name + ".png").c_str());
   if (!result) {
     O3D_ERROR(service_locator())
         << "Failed to save screen into " << file_name;
   }
   return result;
 #else
   // Not a test build, always return false.
   return false;
 #endif
 }
 
 const int* RendererGL::GetRGBAUByteNSwizzleTable() {
   static int swizzle_table[] = { 0, 1, 2, 3, };
   return swizzle_table;
 }
 
 // This is a factory function for creating Renderer objects.  Since
 // we're implementing GL, we only ever return a GL renderer.
 Renderer* Renderer::CreateDefaultRenderer(ServiceLocator* service_locator) {
   return RendererGL::CreateDefault(service_locator);
 }
 
 }  // namespace o3d