[Bug 111241] Shadertoy shader causing hang

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111241

--- Comment #3 from Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer at amd.com> ---
Here's my understanding of the issue.

This shader uses 2 passes:
 - the first pass has BufferA as input and output and does:

if (first frame)
  // init bufferA content
else
  // do something useful

 - the 2nd pass has BufferA as input and does:

N = texelFetch(bufferA)
for(i=0; i < N; i++)
  // do something


The problem here is the "// init bufferA content": it fails to initialize the
buffer content properly, leading to an infinite loop in the 2nd pass.

The exact code is:
   if (iFrame==0) { O -= O; return; }

If one replaces this line with:
   if (iFrame==0) { O = vec4(0.0f); return; }

The shader works fine (you can test the modified version here:
https://www.shadertoy.com/view/wtSXzw ).

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