I have a working render to texture toy iOS app. The issue is it has a ton of jaggies because it is point sampled and not anti-aliasied:
I increased the sample count in my MTKView
subclass to 4
to enable MSAA.
Here is what the relevant code looks like.
// 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;
}
I attach a color and depth buffer configured for MSAA to 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)
In my draw loop I am getting the following error from my fragment shader that consumes the texture that was rendered into:
failed assertion Fragment Function(finalPassOverlayFragmentShader
):
incorrect type of texture (MTLTextureType2DMultisample
) bound at texture binding at index 0 (expect MTLTextureType2D
) for underlay[0]
This is the fragment shader:
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;
}
I am sure I have missed a setting somewhere but I cannot find it.
What have I missed here?
I now have MSAA happening for my 2-pass toy. The only problem is there is not much anti-aliasing happening. In fact it is hard to tell that anything has changed. Here are my latest settings
// 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
The jaggies appear to be from the render-to-texture and not in the asset. Below is a side by side comparison. the top image is rendered using a single pass with MSAA enabled. The bottom image is rendered to texture. The jaggies are clearly visible in the bottom image
The error is not about your render target (a.k.a. color and depth attachments). It's about a texture you're passing in via the render command encoder's fragment texture table — that is, where you're calling setFragmentTexture(_:index:)
. The one you're passing for index 0 is a .type2DMultisample
when the shader is coded to expect .type2D
, because you declared underlay
as a texture2d<...>
.
Your setup for MSAA is OK for an intermediate step. You will eventually need to resolve the texture to a non-multisampled texture in order to draw it to screen. For that step (which might be for this render command encoder or a later one, depending on your needs), you need to set the storeAction
for the color attachment to either .multisampleResolve
or .storeAndMultisampleResolve
. And you need to set the resolveTexture
to a 2D texture. That could be one of your own or a drawable's texture.