只需将金属碎片着色器设置为透明颜色即可

Question

我有一个简单的管道描述符

 let p = MTLRenderPipelineDescriptor()
 ...
 p.colorAttachments[0].pixelFormat = .bgra8Unorm

背景是纯蓝色

 let bg = MTLClearColor(red: 0, green: 0, blue: 1, alpha: 1)
 let pass = MTLRenderPassDescriptor()
 pass.colorAttachments[0].loadAction = .clear
 pass.colorAttachments[0].clearColor = bg

我只是在上面画一个多边形，说一个红色的：

fragment half4 fattie_fragment() {
    return half4(1,0,0, 1);
}

还是绿色...

fragment half4 fattie_fragment() {
    return half4(0,1,0, 1);
}

如果您希望三角形颜色透明，在金属中该怎么办？

fragment half4 fattie_fragment() {
    return half4(0,1,0, 0.275);
}

(注意 - 待定 我不希望整体视图是透明的。只是着色器，绘制的三角形。

Answer 1

配置渲染管线描述符时，请启用混合并选择一组合适的混合因子和操作。例如：

let p = MTLRenderPipelineDescriptor()
...
p.colorAttachments[0].isBlendingEnabled = true
p.colorAttachments[0].rgbBlendOperation = .add
p.colorAttachments[0].alphaBlendOperation = .add
p.colorAttachments[0].sourceAlphaBlendFactor = .sourceAlpha
p.colorAttachments[0].destinationAlphaBlendFactor = .oneMinusSourceAlpha
p.colorAttachments[0].sourceRGBBlendFactor = .sourceAlpha
p.colorAttachments[0].destinationRGBBlendFactor = .oneMinusSourceAlpha