Blending on image output of render TOP

General TouchDesigner Discussion
1

Is there any way to enable blending for Image Outputs of the renderTOP? As I understand it, the following options are available (pls correct me if assumptions are wrong):

1/ Additional color buffers, using render select TOP and layout(..) out vec4 oBuffer

  • These can use blending if the “Allow blending for extra buffers” is turned on
  • However, they MUST be the same resolution and bit depth as the renderTOP

2/ Image output using imageStore()

  • afaik, cannot enable blending
  • However, they can be any resolution / bit depth, indep of each other and the render

My question is: Can I leverage the indep resolutions/bit depth without sacrificing blending? Is this a limitation of imageStore()? can I write the blending in the shader in any way? or approximate it with atomic operations? if not, what is the write protocol - the last fragment draw wins?

Use case: simulation with 5m particles each contributing to various ‘environmental’ layers like nutrients, sediment, temperature, etc. Some need to be 32 bit, some can be 8bit only, some need to be the simulation res, and some need to be the render res

2

You’d need to load the current pixel value using imageLoad(), apply the blending equation yourself using the existing value and the new incoming value, and then write out the results. image uniforms have no notion of blending themselves.

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