Shader constant instance. Assigns a unsigned integer constant to a material instance.
Shaders are parsed on initialization, but not actually compiled until creation of a graphics pipeline. Shader constants implement Vulkan specialization constants and are a powerful way to compile specialized versions of shaders per material instance. Graphics and compute pipeline keys are distinguished by a shader constant hash that is generated from the material instance resource. This way you can benefit from compiler optimizations like loop unrolling and branch elimination per material setup.
layout (constant_id = 0) const uint SAMPLE_COUNT = 8;
layout (constant_id = 1) const uint USE_EXPENSIVE_ROUTINE = 0;
// main()
// Loop unrolling
for (uint i = 0; i < SAMPLE_COUNT; i++)
{
// Perform expensive texture samples here
}
// Branch elimination
if (USE_EXPENSIVE_ROUTINE > 0)
{
// Perform an expensive computation here
}
else
{
// Exit early here
}
