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Editorial Team
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Asked: 2026-06-01T20:10:51+00:00

Using image load and store, i would like to do the following in GLSL

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Using image load and store, i would like to do the following in GLSL 4.2:

vec3 someColor = ...;
vec4 currentPixel = imageLoad(myImage, uv);
float a = currentPixel.a/(currentPixel.a+1.0f);
vec4 newPixel = vec4(currentPixel.rgb*a+someColor*(1.0f-a),currentPixel.a+1.0f);
imageStore(myImage, uv, newPixel);

the value for ‘uv’ can be the same for multiple rasterized pixels. In order to get the proper result, of course I want no other shaderexecution to write into my pixel inbetween the calls of imageLoad() and imageStore();

Is this possible to do somehow with memoryBarrier? if so, how does it have to be used in this code?

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1 Answer

  1. Editorial Team

    the value for ‘uv’ can be the same for multiple rasterized pixels.

    Then you can’t do it.

    memoryBarrier is not a way to create an atomic operation. It only guarantees the ordering for a single shader’s operation. So if a particular shader invocation reads an image, writes it, and then reads it again, you need a memoryBarrier to ensure that what is read is what was written before. If some other shader invocation wrote to it, then you’re out of luck (unless it was a dependent invocation. The rules for this stuff are complex).

    If you’re trying to do programmatic blending, then you need to make certain that each fragment shader invocation reads/writes to a unique value. Otherwise, it’s not going to work.

    You don’t say what it is you’re trying to actually achieve, so it’s not possible to provide a better way of getting what you want. All I can say is that this way is not going to work.

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