Fog-of-war | briefly describe how it work here : Draw the field of view | Graphics library

Looking through the code and through Metal documentation and Metal Shading Language specification, I think I know why you get this error.

If you look through render_command interface that is present in metal_command_buffer header in Metal, you'll find that to pass parameters to indirect render commands, you only have these functions: set_vertex_buffer and set_fragment_buffer, there is no set_vertex_texture or set_vertex_sampler like you have in MTLRenderCommandEncoder.

But, since your pipeline uses shader that in turn uses textures as arguments and you indicate by using supportIndirectCommandBuffers that you would like to use this pipeline in indirect commands, Metal has no choice but to fail pipeline creation.

Instead if you want to pass textures or samplers to indirect render commands, you should use argument buffers, that you will pass to the shader that issues indirect render commands, which in turn will bind them using set_vertex_buffer and set_fragment_buffer for each render_command.

Specification: Metal Shading Language Specification (Section 5.16)

OK after much research I've been unable to find a direct solution. But I have implemented an indirect solution.

You should use a shader for this instead. OnRenderImage requires piping the data back to the CPU and processing it linearly there (slow!!!¹) rather than in parallel on the GPU.

This will take a little bit of research to do properly, but the concept is pretty straight forward. You need to use the stencil mask to get the desired effect. The "white polygon" you have writes data (literally setting a bit to 1 instead of 0) to the stencil mask and then the rest of the scene gets rendered, but only where the stencil mask is a 1.

Basically think of the line of sight polygon as telling the camera where it's allowed to draw other things. Which is what a mask is. The stencil mask is just a specific grouping of bits that are available during rendering that aren't data that gets drawn to the screen, but rather persist across rendering passes. So:

Pass 1: draw the LOS object to the mask buffer.
Pass 2: render the scene only where the buffer has been modified.

I wrote up an outline shader that uses the stencil mask, which you could use as an example and get started. Mind, that shader was writen to apply only to a single object (and "creates" new geometry), but the same process should still work for doing what you're attempting (I just haven't tried to do it myself).

Looks like this thread has a (partial) shader that has the effect you're looking for.

I created two shaders of the standard affair and modified as follows: Hidden Shader: Just under the auto generated shader line "LOD 200", add: