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OpenGL display artifact on W7100

Question asked by tom73 on Jun 15, 2015
Latest reply on Jun 17, 2015 by tom73

  Hi all,


I am facing a display issue on a w7100 card with catalyst 14.502 driver. I reduce the problem to a very simple one.


Generate a RGBA32F fbo.

Clear the fbo content to 0.

Draw a first textured-quad in this fbo

Draw a second textured-quad in this fbo


The quads are drawn using the following fragment shader:

uniform sampler2DRect src;

uniform sampler2DRect dst;


void main(void) {

    vec4 dst = texture2DRect(dst, gl_FragCoord.xy);

    vec4 src = texture2DRect(src, gl_TexCoord[0].xy);

    src.rgb = src.rgb * 0.5f;

    src.a = 0.5f;


    gl_FragColor = src + dst;



Doing so, I accumulate the content of the 2 quads in the destination fbo.


Then, I draw the texture attached to the framebuffer on the display using the following fragment shader:

uniform sampler2DRect src;


void main(void) {

    vec4 tex = texture2DRect(src, gl_TexCoord[0].xy);

    if (tex.a != 0.0f) {

        tex /= tex.a;


    gl_FragColor = tex;



To ensure synchronisation between the read and write operations on the framebuffer, I both try glFlush/glFinish and using glFence. None of them give me a correct result.

I tested this very simple code on HD7700, W8000 and some other gpus, with no issues. I suppose something is wrong in my way of rendering, but there is change in the rendering behavior of Tonga family.


Could you please help me in fixing this simple thing ?