CODEWITHSUNDEEP
iosgraphicsmetalmetalkit
wing
wing

Reputation: 25

MSL - How to specify uniform array parameters in Metal shader?

I'm trying to pass an uniform array into a Metal shader, e.g.:

fragment vec4 fragment_func(constant float4& colors[3] [[buffer(0)]], ...) {...}

I'm getting the error:

"NSLocalizedDescription" : "Compilation failed: \n\nprogram_source:2:1917: error: 'colors' declared as array of references of type 'const constant float4 &'\nprogram_source:2:1923: 
error: 'buffer' attribute cannot be applied to types\nprogram_source:2:1961:

I understand that the 'buffer' attribute can only be applied to pointers and references. In that case, what's the correct way to pass in uniform arrays in MSL?

Edit: MSL specs state that "Arrays of buffer types" are supported for buffer attributes. I must be doing something syntactically wrong?

Upvotes: 0

Views: 1511

Answers (2)

warrenm
warrenm

Reputation: 31782

Arrays of references aren't permitted in C++, nor does MSL support them as an extension.

However, you can take a pointer to the type contained in the array:

fragment vec4 fragment_func(constant float4 *colors [[buffer(0)]], ...) {...}

If necessary, you can pass the size of the array as another buffer parameter, or you can just ensure that your shader function doesn't read more elements than are present in the buffer.

Accessing elements is then as simple as an ordinary dereference:

float4 color0 = *colors;   // or, more likely:
float4 color2 = colors[2];

Upvotes: 3

Danger Ranger
Danger Ranger

Reputation: 151

You may also use:

fragment vec4 fragment_func(constant float4 colors [[buffer(0)]][3], ...) {...}

This is an unfortunate side-effect of how the attribute syntax works in C++. The advantage of doing it this way is that it retains the type on colors more directly.

Upvotes: 2

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