GL_BLEND example c c++ objc

[GL_BLEND example] Following code fragment shows a GL_BLEND example. When drawing GL shapes, you can control how to blend images by calling glBlendFunc() function. To enable blending, you should call glEnable(GL_BLEND) before calling glBlendFunc() function. [GL_BLEND example]

 glEnable(GL_BLEND);  // Enable blending.

  glBlendFunc(GL_ONE, GL_ZERO);  //  Just the source image.

 

  glBegin(GL_TRIANGLES);  // Drawing Using Triangles

  glColor4f(1.0f, 0.0f, 0.0f, 1.0f);

  glVertex4f( 0.0f, 1.2f, 0.0f, 1.0f); 

  glVertex4f(-1.2f,-1.0f, 0.0f, 1.0f); 

  glVertex4f( 1.2f,-1.0f, 0.0f, 1.0f); 

  glEnd(); 

 // Alpha blending.

  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);  

  glBegin(GL_QUADS);  // Draw A Quad

  glColor4f(0.0f, 0.0f, 1.0f, 0.5f);

  glVertex4f(-1.0f, 1.0f, 0.0f, 1.0f); 

  glVertex4f( 1.0f, 1.0f, 0.0f, 1.0f); 

  glVertex4f( 1.0f,-1.0f, 0.0f, 1.0f); 

  glVertex4f(-1.0f,-1.0f, 0.0f, 1.0f); 

  glEnd();