[MetalKit]Using MetalKit part 7使

本系列文章是对 http://metalkit.org 上面MetalKit内容的全面翻译和学习.

MetalKit系统文章目录

有一个读者联系我说我看到一个非常奇怪的现象:当运行我们教程的代码时,MTLLibrary会在几百次绘制调用后返回nil.这让我意识到,我没有考虑到根据文档Metal documentation有些Metal对象是暂时的而有些则不是.谢谢Mike的提醒!

要解决这个问题,我们需要再一次重构代码.这其实是件好事.我们需要把非瞬时的Metal对象(devices, queues, data buffers, textures, states和pipelines)从drawRect(_:)中拿出来,把它们放到视图加载时只执行一次的方法里.命令缓冲器和编码器是仅有的两个瞬时对象,设计出来供一次性使用的,所以我们可以在每次绘制调用时创建它们.
我们将继续从本系列的第5部分 part 5 开始.让我们创建一个新方法-一个初始化方法-它只在视图加载时运行一次:

required init(coder: NSCoder) {
    super.init(coder: coder)
    device = MTLCreateSystemDefaultDevice()
    createBuffers()
    registerShaders()
}

下一步,删除render()方法及在drawRect(_:)中的调用,因为我们不再需要它了.然后从sendToGPU()移动所有代码到drawRect(_:)中,并删除sendToGPU()因为这个也不需要了.这样我们就从drawRect(_:)中移出了所有非瞬时的对象,只保留了command buffer命令缓冲和encoder编码器在里面,只有它们是瞬时对象.

override func drawRect(dirtyRect: NSRect) {
    super.drawRect(dirtyRect)
    if let rpd = currentRenderPassDescriptor, drawable = currentDrawable {
        rpd.colorAttachments[0].clearColor = MTLClearColorMake(0.5, 0.5, 0.5, 1.0)
        let command_buffer = device!.newCommandQueue().commandBuffer()
        let command_encoder = command_buffer.renderCommandEncoderWithDescriptor(rpd)
        command_encoder.setRenderPipelineState(rps)
        command_encoder.setVertexBuffer(vertex_buffer, offset: 0, atIndex: 0)
        command_encoder.setVertexBuffer(uniform_buffer, offset: 0, atIndex: 1)
        command_encoder.drawPrimitives(.Triangle, vertexStart: 0, vertexCount: 3, instanceCount: 1)
        command_encoder.endEncoding()
        command_buffer.presentDrawable(drawable)
        command_buffer.commit()
    }
}

最后,我们创建一个新的类命名为MathUtils,并将两个结构体移动到里面,这样我们就有了一个干净的视图类.

import simd

struct Vertex {
    var position: vector_float4
    var color: vector_float4
}

struct Matrix {
    var m: [Float]
    
    init() {
        m = [1, 0, 0, 0,
            0, 1, 0, 0,
            0, 0, 1, 0,
            0, 0, 0, 1
        ]
    }
    
    func translationMatrix(var matrix: Matrix, _ position: float3) -> Matrix {
        matrix.m[12] = position.x
        matrix.m[13] = position.y
        matrix.m[14] = position.z
        return matrix
    }
    
    func scalingMatrix(var matrix: Matrix, _ scale: Float) -> Matrix {
        matrix.m[0] = scale
        matrix.m[5] = scale
        matrix.m[10] = scale
        matrix.m[15] = 1.0
        return matrix
    }
    
    func rotationMatrix(var matrix: Matrix, _ rot: float3) -> Matrix {
        matrix.m[0] = cos(rot.y) * cos(rot.z)
        matrix.m[4] = cos(rot.z) * sin(rot.x) * sin(rot.y) - cos(rot.x) * sin(rot.z)
        matrix.m[8] = cos(rot.x) * cos(rot.z) * sin(rot.y) + sin(rot.x) * sin(rot.z)
        matrix.m[1] = cos(rot.y) * sin(rot.z)
        matrix.m[5] = cos(rot.x) * cos(rot.z) + sin(rot.x) * sin(rot.y) * sin(rot.z)
        matrix.m[9] = -cos(rot.z) * sin(rot.x) + cos(rot.x) * sin(rot.y) * sin(rot.z)
        matrix.m[2] = -sin(rot.y)
        matrix.m[6] = cos(rot.y) * sin(rot.x)
        matrix.m[10] = cos(rot.x) * cos(rot.y)
        matrix.m[15] = 1.0
        return matrix
    }
    
    func modelMatrix(var matrix: Matrix) -> Matrix {
        matrix = rotationMatrix(matrix, float3(0.0, 0.0, 0.1))
        matrix = scalingMatrix(matrix, 0.25)
        matrix = translationMatrix(matrix, float3(0.0, 0.5, 0.0))
        return matrix
    }
}

运行程序确保你仍能看到壮丽的三角形,就像我们上一部分看到的那样.
源代码source code 已发布在Github上.
下次见!