如何为渲染到纹理 iOS 应用启用 MSAA

Question

我有一个工作渲染到纹理玩具 iOS 应用程序。问题是它有很多锯齿，因为它是点采样而不是抗锯齿的：

我将 MTKView 子类中的样本计数增加到 4 以启用 MSAA。

下面是相关代码的样子。

// render to texture render pass descriptor
renderPassDesc = MTLRenderPassDescriptor()
renderPassDesc.EI_configure(clearColor: MTLClearColorMake(1, 1, 1, 1), clearDepth: 1)

// my MTLRenderPassDescriptor extension convenience method
public func EI_configure(clearColor:MTLClearColor, clearDepth: Double) {

    // color
    colorAttachments[ 0 ] = MTLRenderPassColorAttachmentDescriptor()
    colorAttachments[ 0 ].storeAction = .store
    colorAttachments[ 0 ].loadAction = .clear
    colorAttachments[ 0 ].clearColor = clearColor

    // depth
    depthAttachment = MTLRenderPassDepthAttachmentDescriptor()
    depthAttachment.storeAction = .dontCare
    depthAttachment.loadAction = .clear
    depthAttachment.clearDepth = clearDepth;

}

我将针对 MSAA 配置的颜色和深度缓冲区附加到 renderPassDesc：

// color
let colorDesc = MTLTextureDescriptor.texture2DDescriptor(pixelFormat:view.colorPixelFormat, width:Int(view.bounds.size.width), height:Int(view.bounds.size.height), mipmapped:false)
colorDesc.mipmapLevelCount = 1;
colorDesc.textureType = .type2DMultisample
colorDesc.sampleCount = view.sampleCount
colorDesc.usage = [.renderTarget, .shaderRead]
renderPassDesc.colorAttachments[ 0 ].texture = view.device!.makeTexture(descriptor:colorDesc)

// depth
let depthDesc = MTLTextureDescriptor.texture2DDescriptor(pixelFormat:.depth32Float, width:Int(view.bounds.size.width), height:Int(view.bounds.size.height), mipmapped:false)
depthDesc.mipmapLevelCount = 1;
depthDesc.textureType = .type2DMultisample
depthDesc.sampleCount = view.sampleCount
depthDesc.usage = .renderTarget
renderPassDesc.depthAttachment.texture = view.device!.makeTexture(descriptor:depthDesc)

在我的绘制循环中，我从片段着色器中收到以下错误，该错误消耗了渲染到的纹理：

断言片段函数失败（finalPassOverlayFragmentShader）： 纹理类型不正确 (MTLTextureType2DMultisample) 绑定在索引 0 处的纹理绑定处（预期 MTLTextureType2D）为 underlay[0]

这是片段着色器：

fragment float4 finalPassOverlayFragmentShader(InterpolatedVertex vert [[ stage_in ]],
                                               texture2d<float> underlay [[ texture(0) ]],
                                               texture2d<float> overlay [[ texture(1) ]]) {

    constexpr sampler defaultSampler;

    float4 _F = overlay.sample(defaultSampler, vert.st).rgba;

    float4 _B = underlay.sample(defaultSampler, vert.st).rgba;

    float4 rgba = _F + (1.0f - _F.a) * _B;

    return rgba;
}

我确定我错过了某处的设置，但我找不到它。

我在这里错过了什么？

更新 0

现在我的 2-pass 玩具正在发生 MSAA。唯一的问题是没有太多的抗锯齿发生。事实上，很难说发生了什么变化。这是我的最新设置

// color - multi-sampled texture target
let desc = MTLTextureDescriptor.texture2DDescriptor(pixelFormat:format, width:w, height:h, mipmapped:false)
desc.mipmapLevelCount = 1;
desc.textureType = .type2DMultisample
desc.sampleCount = view.sampleCount
desc.usage = .renderTarget
let tex:MTLTexture? = view.device!.makeTexture(descriptor:desc)

// color - point-sampled resolve-texture
let resolveDesc = MTLTextureDescriptor.texture2DDescriptor(pixelFormat:format, width:w, height:h, mipmapped:true)
let resolveTex:MTLTexture? = view.device!.makeTexture(descriptor:resolveDesc)

// depth texture target
let depthDesc = MTLTextureDescriptor.texture2DDescriptor(pixelFormat:.format, width:w, height:h, mipmapped:false)
depthDesc.mipmapLevelCount = 1;
depthDesc.textureType = .type2DMultisample
depthDesc.sampleCount = view.sampleCount
depthDesc.usage = .renderTarget
let depthTex:MTLTexture? = view.device!.makeTexture(descriptor:depthDesc)

// render pass descriptor
renderPassDesc = MTLRenderPassDescriptor()
// color
renderPassDesc.colorAttachments[ 0 ] = MTLRenderPassColorAttachmentDescriptor()
renderPassDesc.colorAttachments[ 0 ].storeAction = .storeAndMultisampleResolve
renderPassDesc.colorAttachments[ 0 ].loadAction = .clear
renderPassDesc.colorAttachments[ 0 ].clearColor = MTLClearColorMake(0.25, 0.25, 0.25, 1)
renderPassDesc.colorAttachments[ 0 ].texture = tex
renderPassDesc.colorAttachments[ 0 ].resolveTexture = resolveTex
// depth
renderPassDesc.depthAttachment = MTLRenderPassDepthAttachmentDescriptor()
renderPassDesc.depthAttachment.storeAction = .dontCare
renderPassDesc.depthAttachment.loadAction = .clear
renderPassDesc.depthAttachment.clearDepth = 1;
renderPassDesc.depthAttachment.texture = depthTex

更新 1

锯齿似乎来自渲染到纹理，而不是资产中。下面是并排比较。 top 图像使用启用 MSAA 的单通道渲染。 底部 图像被渲染为纹理。锯齿在底部图像中清晰可见

单程

2-pass

Answer 1

错误与您的渲染目标无关（也就是颜色和深度附件）。它是关于您通过渲染命令编码器的片段纹理表传入的纹理——也就是说，您在其中调用setFragmentTexture(_:index:)。当着色器被编码为期望.type2D 时，您为索引0 传递的那个是.type2DMultisample，因为您将underlay 声明为texture2d<...>。

您的 MSAA 设置可以用于中间步骤。您最终需要将纹理解析为非多重采样纹理才能将其绘制到屏幕上。对于该步骤（可能用于此渲染命令编码器或更高版本，取决于您的需要），您需要将颜色附件的storeAction 设置为.multisampleResolve 或.storeAndMultisampleResolve。您需要将resolveTexture 设置为2D 纹理。这可能是您自己的纹理之一或可绘制的纹理。