Why does using glsl or defining functions in a SceneKit shader modifier produce only errors?

Question

Every time I attempt to write a SceneKit shader modifier, I get a pink screen and a debug screen filled with errors. According to the documents, I should be able to write a SceneKit shader modifier in glsl, but all I get is these errors like

error: use of undeclared identifier 'vec3'; did you mean 'vec'?

Huh? Why can't I use vec3?

I've tried converting all vec3 to float3 manually, like this

#pragma arguments

float3 myFunction()
{
    return float3(1,1,1);
}

#pragma transparent
#pragma body

float3 myVar = myFunction();

but then I just get an error like

[SceneKit] Error: FATAL ERROR : failed compiling shader:
Error Domain=MTLLibraryErrorDomain Code=3 "Compilation failed: 

program_source:2847:41: error: expected parameter declarator
                                      , constant return& float3
                                        ^
program_source:2847:50: error: expected ')'
                                      , constant return& float3
                                                 ^
program_source:2732:38: note: to match this '('
fragment SCNOutput commonprofile_frag(commonprofile_io                 in                               [[ stage_in  ]]
                                     ^
program_source:3340:2: error: expected function body after function declarator
}
 ^
" UserInfo={NSLocalizedDescription=Compilation failed: 

program_source:2847:41: error: expected parameter declarator
                                      , constant return& float3
                                        ^
program_source:2847:50: error: expected ')'
                                      , constant return& float3
                                                 ^
program_source:2732:38: note: to match this '('
fragment SCNOutput commonprofile_frag(commonprofile_io                 in                               [[ stage_in  ]]
                                     ^
program_source:3340:2: error: expected function body after function declarator
}
 ^
}
2019-08-31 20:30:28.724039-0700 zLab[3725:903320] [SceneKit] Error: FATAL ERROR : failed compiling shader:
Error Domain=MTLLibraryErrorDomain Code=3 "Compilation failed: 

program_source:2847:41: error: expected parameter declarator
                                      , constant return& float3
                                        ^
program_source:2847:50: error: expected ')'
                                      , constant return& float3
                                                 ^
program_source:2732:38: note: to match this '('
fragment SCNOutput commonprofile_frag(commonprofile_io                 in                               [[ stage_in  ]]
                                     ^
program_source:3340:2: error: expected function body after function declarator
}
 ^
" UserInfo={NSLocalizedDescription=Compilation failed: 

program_source:2847:41: error: expected parameter declarator
                                      , constant return& float3
                                        ^
program_source:2847:50: error: expected ')'
                                      , constant return& float3
                                                 ^
program_source:2732:38: note: to match this '('
fragment SCNOutput commonprofile_frag(commonprofile_io                 in                               [[ stage_in  ]]
                                     ^
program_source:3340:2: error: expected function body after function declarator
}
 ^
}

What does all this mean? What am I doing wrong?

Are you trying to code in GLSL or Metal? Because they're not the same shading language. — Nicol Bolas, Sep 01 '19 at 04:06
@NicolBolas You mean MSL? I'm trying to code in GLSL. But when GLSL failed, I also tried MSL. They are both failing. — zakdances, Sep 01 '19 at 04:10

score 2 · Accepted Answer · answered Sep 01 '19 at 11:09

2

The #pragma arguments directive should be used to declare parameters of the shader modifier that are set from the CPU client code.

For custom functions and helpers you can use the #pragma declaration instruction (see also Custom Variable Declarations Using Metal With Scene Kit Shader Modifiers)

answered Sep 01 '19 at 11:09

mnuages

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Thank you, this works, but the mystery remains unsolved: why do the docs have an example with a custom function definition below `#pragma arguments` in apparent contradiction with your answer? – zakdances Sep 02 '19 at 04:08
Yeah. This is a documentation issue. – mnuages Sep 02 '19 at 10:13

Why does using glsl or defining functions in a SceneKit shader modifier produce only errors?

1 Answers1