How do I pass a Float uniform to iOS Metal shader using Swift?

Question

I want to pass a float to my metal shader. I cannot figure out how.

Here is my shader:

vertex float4 model_vertex(unsigned int iid[[instance_id]]
                           constant float angle) {
    float number = float(iid) / 64.0;
    return float4(number * sin(angle), number * cos(angle), 0.0, 1.0);
}

Now I want to pass it to the shader:

let renderPassDescriptor = MTLRenderPassDescriptor()
let renderEncoder = commandBuffer.renderCommandEncoderWithDescriptor(renderPassDescriptor)
// ...
let angle: Float = 0.5
renderEncoder.setUniform1(angle) // What do I do here?

How do I pass the single float value?

Wil Shipley · Answer 1 · 2016-08-12T22:07:27.153

11

Also in 10.11+ and iOS 9+ you can use:

public func setVertexBytes(bytes: UnsafePointer<Void>, length: Int, atIndex index: Int)

Which is documented to be better than creating a MTLBuffer if you're only using the buffer once (and your data is less than 4K long).

edited Aug 12 '16 at 22:07

answered Sep 12 '15 at 20:54

Wil Shipley

9,343
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59

1

Maybe this is obvious, but OP's question has a vertex shader and `setFragmentBytes` sends data to fragment shaders, so if like OP you want to send data to a vertex shader use `setVertexBytes` instead. – Bjorn Aug 11 '16 at 14:36

score 8 · Accepted Answer · answered Oct 15 '14 at 23:07

I haven't seen setUniform* before. To pass uniforms to your vertex shader, use:

setVertexBuffer(buffer: MTLBuffer?, offset: Int, atIndex index: Int)

Where buffer would be an array with a single float, in your example. To pass uniforms to a fragment shader use setFragmentBuffer.

How do I pass a Float uniform to iOS Metal shader using Swift?

2 Answers2