Shaders.metal only get the y value of the mouse - macos

Question

I want to use mouse to control camera position computed by compute function. in my view code:
import MetalKit
public class MetalView: MTKView, NSWindowDelegate {
var queue: MTLCommandQueue! = nil
var cps: MTLComputePipelineState! = nil
var timer: Float = 0
var timerBuffer: MTLBuffer!
var mouseBuffer: MTLBuffer!
var pos: NSPoint!
required public init(coder: NSCoder) {
super.init(coder: coder)
self.framebufferOnly = false
device = MTLCreateSystemDefaultDevice()
registerShaders()
}
override public func drawRect(dirtyRect: NSRect) {
super.drawRect(dirtyRect)
if let drawable = currentDrawable {
let command_buffer = queue.commandBuffer()
let command_encoder = command_buffer.computeCommandEncoder()
command_encoder.setComputePipelineState(cps)
command_encoder.setTexture(drawable.texture, atIndex: 0)
command_encoder.setBuffer(timerBuffer, offset: 0, atIndex: 1)
command_encoder.setBuffer(mouseBuffer, offset: 0, atIndex: 2)
update()
let threadGroupCount = MTLSizeMake(8, 8, 1)
let threadGroups = MTLSizeMake(drawable.texture.width / threadGroupCount.width, drawable.texture.height / threadGroupCount.height, 1)
command_encoder.dispatchThreadgroups(threadGroups, threadsPerThreadgroup: threadGroupCount)
command_encoder.endEncoding()
command_buffer.presentDrawable(drawable)
command_buffer.commit()
}
}
func registerShaders() {
queue = device!.newCommandQueue()
do {
let library = device!.newDefaultLibrary()!
let kernel = library.newFunctionWithName("compute")!
timerBuffer = device!.newBufferWithLength(sizeof(Float), options: [])
mouseBuffer = device!.newBufferWithLength(sizeof(NSPoint), options: [])
cps = try device!.newComputePipelineStateWithFunction(kernel)
} catch let e {
Swift.print("\(e)")
}
}
func update() {
timer += 0.01
var bufferPointer = timerBuffer.contents()
memcpy(bufferPointer, &timer, sizeof(Float))
bufferPointer = mouseBuffer.contents()
memcpy(bufferPointer, &pos, sizeof(NSPoint))
}
override public func mouseDragged(event: NSEvent) {
pos = convertPointToLayer(convertPoint(event.locationInWindow, fromView: nil))
let scale = layer!.contentsScale
pos.x *= scale
pos.y *= scale
debugPrint("Hello",pos.x,pos.y)
}
}
and my shader code:
kernel void compute(texture2d<float, access::write> output [[texture(0)]],
constant float &timer [[buffer(1)]],
constant float2 &mouse [[buffer(2)]],
uint2 gid [[thread_position_in_grid]])
{
int width = output.get_width();
int height = output.get_height();
float2 uv = float2(gid) / float2(width, height);
uv = uv * 2.0 - 1.0;
// scale proportionately.
if(width > height) uv.x *= float(width)/float(height);
if(width < height) uv.y *= float(height)/float(width);
float2 mpos = mouse * 2.0 - 1.0;
float3 cameraPosition = float3( mpos.x,mpos.y, -10.0 );///<-- mouse position to set camera position
...
}
But somehow I only get the mpos.y value. It seems like mpos.x is not send over to the compute function. How can I resolve this?

Answer 1

NSPoint's fields are CGFloat. I think the issue is that, for 64-bit, CGFloat is defined as Double, not Float. Metal's float corresponds to Swift's Float, not Double. Presumably, float2 corresponds to two Swift Floats. Your buffer layout is wrong. Copy two Floats, not an NSPoint, into mouseBuffer.