quads.glsl

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#version 430
 
#ifdef VERTEX_SHADER
 
in vec3 position;
 
uniform mat4 mvpMatrix;
 
void main( )
{
    gl_Position= mvpMatrix * vec4(position, 1);
}
#endif
 
 
#ifdef FRAGMENT_SHADER
 
 
#extension GL_KHR_shader_subgroup_ballot : require
 
#ifdef EARLY_TESTS
layout(early_fragment_tests) in;
#endif
 
layout(binding= 0, r32ui) coherent uniform uimage2D image;
 
out vec4 fragment_color;
 
void main( )
{
    //~ imageAtomicAdd(image, ivec2(gl_FragCoord.xy), 1);
    
    // quads
    ivec2 pixel= ivec2(gl_FragCoord.xy);
    ivec2 quad= pixel / 2;
    
    // enumere tous les quads
    while(true)
    {
        ivec2 quad1= subgroupBroadcastFirst( quad );
        
        if( gl_SubgroupInvocationID == subgroupBroadcastFirst( gl_SubgroupInvocationID ) )
            imageAtomicAdd(image, quad1, 1u);   // selectionne un thread du quad
        
        if(quad == quad1)
            break;  // termine les 4 threads du quad
    }
    
    subgroupBarrier();
    
    fragment_color= vec4(1, 0, 0, 1);
}
#endif