Check if callable program is bound?

Gaming and Visualization Technologies Visualization OptiX
1

I’m adding a shader graph system to my renderer. I would like parameters on shading nodes to either have a constant value, or a connection to another node to evaluate to get the value. For instance:

rtDeclareVariable(float3, color_value, , );
rtDeclareVariable(rtCallableProgramId<float3()>, eval_color, , );
rtDeclareVariable(bool, color_is_bound, , );
RT_CALLABLE_PROGRAM float3 shader_node() {
    float3 result = color_value;
    if (color_is_bound) result = eval_color();
    return result;
}

Is there a way of checking if the program is bound without having a manually set flag in there as well? Another alternative would be to bind a different program instead that just supplies the constant value, but this seems like it might be less efficient (or is it)?

What’s the recommended way of doing this?

2

You can set “eval_color” to RT_PROGRAM_ID_NULL on the host side as a sentinel:

context[ "eval_color" ]->setInt( RT_PROGRAM_ID_NULL );

This is guaranteed to never be a valid program id and is described briefly in optix_host.h.

3

Thanks! and on the device side would I just:

if (eval_color == RT_PROGRAM_ID_NULL) {
    result = color_value;
} else {
    result = eval_color();
}

?

And as a follow-up question, would the branch here be more or less efficient than just switching out the program bound to eval_color for another one that returns a default value?

Cheers,

Anders

4

Yes, that should work. Let me know if it doesn’t.

5

And the branch is probably more efficient than the function call, but it would need to be measured if you’re really doing a lot of this.

6

Thanks!