金属顶点着色器绘制纹理的点 [英] Metal vertex shader draw points of a Texture

问题描述

我想执行Metal(或OpenGLES 3.0)着色器，该着色器通过混合绘制点"基元.为此，我需要将纹理的所有像素坐标作为顶点传递给顶点着色器"，以计算要传递给片段着色器的顶点的位置.片段着色器仅在启用混合的情况下输出该点的颜色.我的问题是，是否有一种有效的方法是将顶点的坐标传递给顶点着色器，因为1920x1080图像的顶点过多，而在一秒钟内需要完成30次?就像我们通过使用dispatchThreadgroups命令在计算着色器中所做的一样，不同之处在于计算着色器无法在启用混合的情况下绘制几何图形.

I want to execute Metal (or OpenGLES 3.0) shader that draws Points primitive with blending. To do that, I need to pass all the pixel coordinates of the texture to Vertex shader as vertices which computes the position of the vertex to be passed to fragment shader. The fragment shader simply outputs the color for the point with blending enabled. My problem is if there is an efficient was to pass coordinates of vertices to the vertex shader, since there would be too many vertices for 1920x1080 image, and that needs to be done 30 times in a second? Like we do in a compute shader by using dispatchThreadgroups command, except that compute shader can not draw a geometry with blending enabled.

这就是我所做的-

  let vertexFunctionRed = library!.makeFunction(name: "vertexShaderHistogramBlenderRed")

    let fragmentFunctionAccumulator = library!.makeFunction(name: "fragmentShaderHistogramAccumulator")


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

    do {
        histogramPipelineRed = try device.makeRenderPipelineState(descriptor: renderPipelineDescriptorRed)
    } catch {
        print("Unable to compile render pipeline state Histogram Red!")
        return
    }

绘图代码:

  let commandBuffer = commandQueue?.makeCommandBuffer()
        let renderEncoder = commandBuffer?.makeRenderCommandEncoder(descriptor: renderPassDescriptor!)
        renderEncoder?.setRenderPipelineState(histogramPipelineRed!)
        renderEncoder?.setVertexTexture(metalTexture, index: 0)
        renderEncoder?.drawPrimitives(type: .point, vertexStart: 0, vertexCount: 1, instanceCount: metalTexture!.width*metalTexture!.height)
  renderEncoder?.drawPrimitives(type: .point, vertexStart: 0, vertexCount: metalTexture!.width*metalTexture!.height, instanceCount: 1)

和着色器:

  vertex MappedVertex vertexShaderHistogramBlenderRed (texture2d<float, access::sample> inputTexture [[ texture(0) ]],
                                                 unsigned int vertexId [[vertex_id]])
  {
        MappedVertex out;

constexpr sampler s(s_address::clamp_to_edge, t_address::clamp_to_edge, min_filter::linear, mag_filter::linear, coord::pixel);

ushort width = inputTexture.get_width();
ushort height = inputTexture.get_height();

float X = (vertexId % width)/(1.0*width);
float Y = (vertexId/width)/(1.0*height);

 int red = inputTexture.sample(s, float2(X,Y)).r;

 out.position = float4(-1.0 + (red * 0.0078125), 0.0, 0.0, 1.0);
 out.pointSize = 1.0;
 out.colorFactor = half3(1.0, 0.0, 0.0);

 return out;
 }

   fragment half4 fragmentShaderHistogramAccumulator ( MappedVertex in [[ stage_in ]]
                                              )
 {
    half3 colorFactor = in.colorFactor;
    return half4(colorFactor*(1.0/256.0), 1.0); 
}

推荐答案

也许您可以绘制1920x1080实例的单个点.像这样:

Maybe you can draw a single point instanced 1920x1080 times. Something like:

vertex float4 my_func(texture2d<float, access::read> image [[texture(0)]],
                      constant uint &width [[buffer(0)]],
                      uint instance_id [[instance_id]])
{
    // decompose the instance ID to a position
    uint2 pos = uint2(instance_id % width, instance_id / width);
    return float4(image.read(pos).r * 255, 0, 0, 0);
}

这篇关于金属顶点着色器绘制纹理的点的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！