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?

Answer 1

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).

Answer 2

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.