【发布时间】：2018-06-24 21:04:58
【问题描述】：
我正在尝试实现一个金属支持的绘图应用程序，其中笔触是通过沿路径反复压印一个带纹理的正方形来在 MTKView 上绘制的。我遇到的问题是，虽然每个画笔印章都正确显示了纹理的不透明度，但重叠的正方形不会建立价值，而是相互覆盖。在下面的说明中，每个图章都是一个带有 alpha 分量的带纹理的圆圈
我有一种感觉，因为所有的邮票都是一次渲染的，渲染器没有办法“建立”价值。但是，我对金属技术的了解有点深，所以我希望有人能指出我正确的方向。
以下是进一步的相关信息：
对于单个画笔描边，所有几何图形都存储在一个数组 vertexArrayBrush3DMesh 中，该数组包含所有正方形图章（每个正方形由 2 个三角形组成）。每个顶点的坐标的 z 值为 0.0，这意味着它们都占据相同的 3d“平面”。这可能是一个问题吗？ （我测试了放置随机 z 值，但我没有看到行为的视觉差异）
下面是我的渲染管道设置。请注意，“.isBlendingEnabled = true”和“.alphaBlendingOperation = .add”都被注释掉了，因为它们对解决我的问题没有任何作用
// 5a. Define render pipeline settings
let renderPipelineDescriptor = MTLRenderPipelineDescriptor()
renderPipelineDescriptor.vertexFunction = vertexProgram
renderPipelineDescriptor.sampleCount = self.sampleCount
renderPipelineDescriptor.colorAttachments[0].pixelFormat = self.colorPixelFormat
//renderPipelineDescriptor.colorAttachments[0].isBlendingEnabled = true
//renderPipelineDescriptor.colorAttachments[0].alphaBlendOperation = .add
renderPipelineDescriptor.fragmentFunction = fragmentProgram
请注意，将以下属性添加到 renderPassDescriptor 确实对设置整个画布的透明度有影响
// ensure canvas is transparent
renderPassDescriptor?.colorAttachments[0].loadAction = .clear
renderPassDescriptor?.colorAttachments[0].clearColor = MTLClearColorMake(0, 0, 0, 0)
以下是我进行渲染的代码部分。
func metalRenderColoredMesh(){
// the key to this routine is that it operates on a prepopulated array of points stored in vertexArrayBrush3DMesh
// whenever we want to render the current mesh, this routine gets called from draw()
if vertexArrayBrush3DMesh.count > 1 { // we must have more than 2 points to be able to draw a line
// 6. Set buffer size of objects to be drawn
let dataSize = vertexArrayBrush3DMesh.count * MemoryLayout<Vertex3DColor>.stride // apple recommendation size of the vertex data in bytes
let vertexBuffer: MTLBuffer = device!.makeBuffer(bytes: vertexArrayBrush3DMesh, length: dataSize, options: [])! // create a new buffer on the GPU
let renderPassDescriptor: MTLRenderPassDescriptor? = self.currentRenderPassDescriptor
let samplerState: MTLSamplerState? = defaultSampler(device: self.device!)
let texture = MetalTexture(resourceName: "opaqueRound", ext: "png", mipmaped: true)
texture.loadTexture(device: device!, commandQ: commandQueue, flip: true)
// If the renderPassDescriptor is valid, begin the commands to render into its drawable
if renderPassDescriptor != nil {
// ensure canvas is transparent
renderPassDescriptor?.colorAttachments[0].loadAction = .clear
renderPassDescriptor?.colorAttachments[0].clearColor = MTLClearColorMake(0, 0, 0, 0)
// Create a new command buffer for each tessellation pass
let commandBuffer: MTLCommandBuffer? = commandQueue.makeCommandBuffer()
// 7a. Create a renderCommandEncoder four our renderPipeline
let renderCommandEncoder: MTLRenderCommandEncoder? = commandBuffer?.makeRenderCommandEncoder(descriptor: renderPassDescriptor!)
renderCommandEncoder?.label = "Render Command Encoder"
renderCommandEncoder?.setRenderPipelineState(renderPipeline!)
renderCommandEncoder?.setVertexBuffer(vertexBuffer, offset: 0, index: 0)
renderCommandEncoder?.setFragmentTexture(texture.texture, index: 0)
renderCommandEncoder?.setFragmentSamplerState(samplerState, index: 0)
// most important below: we tell the GPU to draw a set of triangles, based on the vertex buffer. Each triangle consists of three vertices, starting at index 0 inside the vertex buffer, and there are vertexCount/3 triangles total
renderCommandEncoder?.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: vertexArrayBrush3DMesh.count)
///////////renderCommandEncoder?.popDebugGroup()
renderCommandEncoder?.endEncoding() // finalize renderEncoder set up
commandBuffer?.present(self.currentDrawable!) // needed to make sure the new texture is presented as soon as the drawing completes
// 7b. Render to pipeline
commandBuffer?.commit() // commit and send task to gpu
} // end of if renderPassDescriptor
} // end of if vertexArrayBrush3DMesh.count > 1 }// end of func metalRenderColoredMesh()
2017/01/17 更新
在实施@warrenm 提供的建议后，我的笔触看起来无限有希望。
但是，结果出现了一些新问题/问题。
我不确定 Metal 如何处理大于 1 的加色值。它们会被限制在 1 吗？这是我在笔画的饱和部分看到的振铃的原因吗？
由于我实施的贝塞尔曲线采样的不规则性质，笔触的某些区域看起来有些不完整。为了让这种印章方法发挥作用，我必须想出一种方法，让印章均匀分布在整个笔画上。
【问题讨论】：
标签： swift swift3 metal render-to-texture