Accessing OpenGL Buffers

The package GL.Buffers gives access to the OpenGL color buffers, as well as the depth and stencil buffer. There are four color buffers:

• Front left
• Front right
• Back left
• Back right

Front and back are for double-buffered rendering (rendering in one buffer while displaying the other one), left and right are for stereoscopic rendering. Which of the buffers are available depends on your context setup.

You can render to one or more color buffers at a time by setting the current buffer(s) with Set_Active_Buffer(s). You can clear the color buffers with Clear or Clear_Color_Buffers (since OpenGL 3).

To use the depth buffer, you need to create your OpenGL context with more than 0 color depth buffer bits. You also need to enable the depth test with GL.Toggles.Enable (GL.Toggles.Depth_Test);. Same goes for the stencil buffer and test (use GL.Toggles.Stencil_Test).

GL.Blending enables you to setup alpha blending in the color buffer. A typical setup would be:

<?prettify lang=ada?>

GL.Toggles.Enable (GL.Toggles.Blend);
GL.Blending.Set_Blend_Func
  (GL.Blending.Src_Alpha, GL.Blending.One_Minus_Src_Alpha);