ios - Metal API 验证崩溃

Question

我编写了以下代码来为 Metal 纹理的离屏渲染实现加法混合，但如果启用了 Metal API 验证，它会崩溃:

validateRenderPassDescriptor:487: failed assertion `Texture at colorAttachment[0] has usage (0x02) which doesn't specify MTLTextureUsageRenderTarget (0x04)'

代码如下:

let renderPipelineDescriptorGreen = MTLRenderPipelineDescriptor()
renderPipelineDescriptorGreen.vertexFunction = vertexFunctionGreen
renderPipelineDescriptorGreen.fragmentFunction = fragmentFunctionAccumulator
renderPipelineDescriptorGreen.colorAttachments[0].pixelFormat = .bgra8Unorm
renderPipelineDescriptorGreen.colorAttachments[0].isBlendingEnabled = true
renderPipelineDescriptorGreen.colorAttachments[0].rgbBlendOperation = .add
renderPipelineDescriptorGreen.colorAttachments[0].sourceRGBBlendFactor = .one

renderPipelineDescriptorGreen.colorAttachments[0].destinationRGBBlendFactor = .one

我想要实现的只是加色混合，在 OpenGLES 中是这样的:

glBlendEquation(GL_FUNC_ADD);
glBlendFunc(GL_ONE, GL_ONE);
glEnable(GL_BLEND);

我的代码有什么问题？

Answer 1

好的，我找到了解决方案。解决方案是设置纹理使用标志 MTLTextureUsage.renderTarget 除了(或代替取决于使用情况，创建纹理时的 shaderRead 或 shaderWrite:

        let textureDescriptor = MTLTextureDescriptor()
        textureDescriptor.textureType = .type3D
        textureDescriptor.pixelFormat = .bgra8Unorm
        textureDescriptor.width = 256
        textureDescriptor.height = 1
        textureDescriptor.usage = .renderTarget

        let texture = device.makeTexture(descriptor: textureDescriptor)