Metal iOS中的遮罩

Question

我在opengl中做了這樣的蒙版如下

vec4 patCol = texture2D(pattern, samplePos);
vec4 maskCol = texture2D(tex0, texCoordVarying);
gl_FragColor=vec4(patCol.xyz, patCol.w);

我想在iOS中進行相同的遮罩，maskCol中的紋理是半透明的。 當我無法在Metal中獲得類似的輸出時。 任何人都可以在這方面幫助我。

Renderpipeline描述符

let pipelineDescriptor = MTLRenderPipelineDescriptor()
pipelineDescriptor.fragmentFunction = fragmentFunction
pipelineDescriptor.vertexFunction = vertexFunction
pipelineDescriptor.colorAttachments[0].pixelFormat = .bgra8Unorm
pipelineDescriptor.sampleCount = 1
pipelineDescriptor.colorAttachments[0].isBlendingEnabled = true
pipelineDescriptor.colorAttachments[0].rgbBlendOperation = .add
pipelineDescriptor.colorAttachments[0].alphaBlendOperation = .add
pipelineDescriptor.colorAttachments[0].sourceRGBBlendFactor = .one
pipelineDescriptor.colorAttachments[0].sourceAlphaBlendFactor = .one
pipelineDescriptor.colorAttachments[0].destinationRGBBlendFactor = .oneMinusSourceAlpha
pipelineDescriptor.colorAttachments[0].destinationAlphaBlendFactor = .oneMinusSourceAlpha

Answer 1

鑒於您未在退貨中使用maskCol，我將假設您正在嘗試執行以下操作：

    float4 patCol...
    float4 maskCol...
    return float4(patCol.rgb, maskCol.a);

也就是說，從蒙版中獲取alpha值並將其應用於源patCol ...

為了使其正常工作，您需要在pipelineDescriptor中設置混合選項：

    pipelineDescriptor.colorAttachments[0].isBlendingEnabled = true
    pipelineDescriptor.colorAttachments[0].rgbBlendOperation = .add
    pipelineDescriptor.colorAttachments[0].alphaBlendOperation = .add
    pipelineDescriptor.colorAttachments[0].sourceRGBBlendFactor = .sourceAlpha
    pipelineDescriptor.colorAttachments[0].sourceAlphaBlendFactor = .sourceAlpha
    pipelineDescriptor.colorAttachments[0].destinationRGBBlendFactor = .oneMinusSourceAlpha
    pipelineDescriptor.colorAttachments[0].destinationAlphaBlendFactor = .oneMinusSourceAlpha

這將為您提供“默認”行為，即通過源進行混合：source.rgba + destination.rgba