OpenGL Framebuffer ColorAttachment to Compute Shader - c++

Question

I want to put the Color Attachment of my custom framebuffer into a compute shader for simple image processing, but I am getting a black screen only.
Here is my example code
Creating color attachment
glGenFramebuffers(1, &this->fbo);
glBindFramebuffer(GL_FRAMEBUFFER, this->fbo);
glGenTextures(1, &this->textureColorBuffer);
glBindTexture(GL_TEXTURE_2D, this->textureColorBuffer);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, this->width(), this->height(), 0,
GL_RGB, GL_UNSIGNED_BYTE, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
this->textureColorBuffer, 0);
Compiling and linking shader
cshader = glCreateShader(GL_COMPUTE_SHADER);
const char *csSrc[] = {
"#version 440\n",
"layout (binding = 0, rgba32f) uniform image2D destTex;\
layout (binding = 1, rgba32f) uniform image2D sourceTex;\
layout (local_size_x = 16, local_size_y = 16, local_size_z = 1) in;\
void main() {\
vec4 texel;\
ivec2 storePos = ivec2(gl_GlobalInvocationID.xy);\
texel = imageLoad(sourceTex, storePos);\
texel = vec4(1.0) - texel;\
imageStore(destTex, storePos, texel);\
}"
};
glShaderSource(cshader, 2, csSrc, NULL);
glCompileShader(cshader);
cshaderprogram = glCreateProgram();
glAttachShader(cshaderprogram, cshader);
glLinkProgram(cshaderprogram);
Invoke Shader and drawing texture to quad. The shader is a simple color switching shader, for testing purposes.
glUseProgram(cshaderprogram);
glUniform1i(0, 0);
glActiveTexture(GL_TEXTURE0);
glBindImageTexture(0, outputTexture, 0, GL_FALSE, 0, GL_WRITE_ONLY,
GL_RGBA32F);
glActiveTexture(GL_TEXTURE1);
glBindImageTexture(0, textureColorBuffer, 0, GL_FALSE, 0, GL_READ_ONLY,
GL_RGBA32F);
glUniform1i(1, 1);
glDispatchCompute(width() / 16, height() / 16, 1);
glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT);
screenProgram.bind();
glBindFramebuffer(GL_FRAMEBUFFER, 0);
glBindVertexArray(screenVao);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, outputTexture);
glDrawArrays(GL_TRIANGLES, 0, 6);
I am able to render the textureColorBuffer to the quad correctly and i can write to a texture. I think the problem that i do not know how to read from the framebuffer.
I hope you can help me. If there are still some questions just ask.

Answer 1

The binding point of sourceTex is 1 and not 0:
layout (binding = 1, rgba32f) uniform image2D sourceTex;
So you have to bind the texture to the image unit 1
glBindImageTexture( 1, // <------- 1 instead of 0
textureColorBuffer, 0, GL_FALSE, 0, GL_READ_ONLY, GL_RGBA32F);
Note, Images units and Texture units are different things.
Of course you can use a texture sampler uniform in the coumpute shader too. If destTex and sourceTex have the same size, you can use texelFetch with gl_GlobalInvocationID, to look up sourceTex:
layout (local_size_x = 16, local_size_y = 16, local_size_z = 1) in;
layout (binding = 0, rgba32f) uniform image2D destTex;
layout (binding = 0) uniform sampler2D sourceTex;
void main()
{
ivec2 pos = ivec2(gl_GlobalInvocationID.xy);
vec4 texel = texelFetch(sourceTex, pos, 0);
texel = vec4(1.0) - texel;
imageStore(destTex, pos, texel);
}
In the above snippet is used the image unit 0 for destTex and the texture unit 0 for sourceTex.
By the way, are you sure that you want to do
texel = vec4(1.0) - texel;
Note, if the alpha channel of texel is 1.0, it will become completely transparent.