I'm noob to webgl. After reading the tutorials at webglfundamentals.org and "Introduction to Computer Graphics", i'm able to succesfully draw some stuff and the depth buffer without thirty-party libraries.

Now, i try to go a step further and apply some visual enhancement to my drawings, by usharp-masking the depth buffer, also called "the cheap SSAO".

What i understand is, that i should:

  • draw the depth buffer
  • blur X
  • blur Y
  • combine the blurred depth buffer with the diffuse component of the initial image

What i learned so far is, that to apply these four steps, i could use two textures, ping-pong back the textures, apply the effects in sequence to the textures and at the end draw to the screen the final result.

It would be easier with a gl.RGB4 color attachment?

It seems to me, that the final effect is just only to dim the diffuse color of the initial image, so i could draw the depth buffer to the red channel, blur-X the red channel to the green channel, blur-Y the green channel to the blue channel, and then combine this last with the initial drawing.

Isn't this faster or memory-cheaper than swapping two textures, for example by thinking mobile-first?

What are the drawbacks? Anyone already tried this? Thanks in advance


1 Answer 1


No, actually is not allowed to read and write to/from the same buffer at the same time. This results in undefined behavior. If it does work on one piece of hardware, it may not work on another. Here is a more detailed explanation: https://www.opengl.org/wiki/Framebuffer_Object#Feedback_Loops

Here is the resulting error:

GL_INVALID_OPERATION> Source and destination textures of the draw are the same.


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