金属材质中同时具有纹理和无纹理，采用混合模式叠加。

Question

金属材质中同时具有纹理和无纹理，采用混合模式叠加。

5

我正在使用Metal绘制两个不同的顶点缓冲区，一个带有纹理（忽略顶点颜色数据），另一个没有纹理（仅绘制顶点颜色数据）：

let commandBuffer = self.commandQueue.makeCommandBuffer()
let commandEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: rpd)

//render first buffer with texture
commandEncoder.setRenderPipelineState(self.rps)
commandEncoder.setVertexBuffer(self.vertexBuffer1, offset: 0, at: 0)
commandEncoder.setVertexBuffer(self.uniformBuffer, offset: 0, at: 1)
commandEncoder.setFragmentTexture(self.texture, at: 0)
commandEncoder.setFragmentSamplerState(self.samplerState, at: 0)
commandEncoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: count1, instanceCount: 1)


//render second buffer without texture
commandEncoder.setRenderPipelineState(self.rps)
commandEncoder.setVertexBuffer(self.vertexBuffer2, offset: 0, at: 0)
commandEncoder.setVertexBuffer(self.uniformBuffer, offset: 0, at: 1)
commandEncoder.setFragmentTexture(nil, at: 0)
commandEncoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: count2, instanceCount: 1)

commandEncoder.endEncoding()
commandBuffer.present(drawable)
commandBuffer.commit()

这个着色器的代码如下：

#include <metal_stdlib>
using namespace metal;

struct Vertex {
    float4 position [[position]];
    float4 color;
    float4 texCoord;
};

struct Uniforms {
    float4x4 modelMatrix;
};

vertex Vertex vertex_func(constant Vertex *vertices [[buffer(0)]],
                          constant Uniforms &uniforms [[buffer(1)]],
                          uint vid [[vertex_id]])
{
    float4x4 matrix = uniforms.modelMatrix;
    Vertex in = vertices[vid];
    Vertex out;
    out.position = matrix * float4(in.position);
    out.color = in.color;
    out.texCoord = in.texCoord;
    return out;
}

fragment float4 fragment_func(Vertex vert [[stage_in]],
                               texture2d<float>  tex2D     [[ texture(0) ]],
                               sampler           sampler2D [[ sampler(0) ]]) {

    if (vert.color[0] == 0 && vert.color[1] == 0 && vert.color[2] == 0) {
        //texture color
        return tex2D.sample(sampler2D, float2(vert.texCoord[0],vert.texCoord[1]));
    }
    else {
        //color color
        return vert.color;
    }

}

有没有更好的方法来做这件事？我想使用纹理的任何顶点都会被设置为黑色，着色器会检查颜色是否为黑色，如果是，则使用纹理，否则使用颜色。

另外，如果彩色多边形和纹理多边形在屏幕上重叠，有没有一种方法可以使用乘法函数混合它们？似乎MTLBlendOperation只有加/减/最小/最大的选项，没有乘法？

- jonydep

我对Metal不熟悉，一直在苦恼如何在顶点数组上使用多个纹理，这个问题会帮助我解决它，我想。 - Hope

1个回答

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- ThreeDeeZero · Accepted Answer

另一种实现该功能的方法是创建两个不同的片段函数，一个用于渲染纹理片段，另一个处理有颜色的顶点。

首先，在加载时需要创建两个不同的MTLRenderPipelineState:

let desc = MTLRenderPipelineDescriptor()    

/* ...load all other settings in the descriptor... */

// Load the common vertex function.
desc.vertexFunction = library.makeFunction(name: "vertex_func")

// First create the one associated to the textured fragment function.
desc.fragmentFunction = library.makeFunction(name: "fragment_func_textured")
let texturedRPS = try! device.makeRenderPipelineState(descriptor: desc)

// Then modify the descriptor to create the state associated with the untextured fragment function.
desc.fragmentFunction = library.makeFunction(name: "fragment_func_untextured")
let untexturedRPS = try! device.makeRenderPipelineState(descriptor: desc)

在渲染时，对于纹理对象的绘制命令编码之前需设置纹理状态；而对于非纹理对象的绘制命令编码之前需切换到非纹理状态。操作步骤如下：

//render first buffer with texture
commandEncoder.setRenderPipelineState(texturedRPS) // Set the textured state
commandEncoder.setVertexBuffer(self.vertexBuffer1, offset: 0, at: 0)
commandEncoder.setVertexBuffer(self.uniformBuffer, offset: 0, at: 1)
commandEncoder.setFragmentTexture(self.texture, at: 0)
commandEncoder.setFragmentSamplerState(self.samplerState, at: 0)
commandEncoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: count1, instanceCount: 1)

//render second buffer without texture
commandEncoder.setRenderPipelineState(untexturedRPS) // Set the untextured state
commandEncoder.setVertexBuffer(self.vertexBuffer2, offset: 0, at: 0)
commandEncoder.setVertexBuffer(self.uniformBuffer, offset: 0, at: 1)
// No need to set the fragment texture as we don't need it in the fragment function.
// commandEncoder.setFragmentTexture(nil, at: 0)
commandEncoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: count2, instanceCount: 1)

顶点函数无需更改。但是需要将片段函数分成两部分：

fragment float4 fragment_func_textured(Vertex vert [[stage_in]],
                                       texture2d<float>  tex2D     [[ texture(0) ]],
                                       sampler           sampler2D [[ sampler(0) ]]) {
    //texture color
    return tex2D.sample(sampler2D, float2(vert.texCoord[0],vert.texCoord[1]));
}

fragment float4 fragment_func_untextured(Vertex vert [[stage_in]]) {
    //color color
    return vert.color;
}

你甚至可以使用两个不同的顶点函数，以输出两个不同的顶点结构，从而节省一些字节。实际上，纹理片段函数只需要texCoord字段而不需要color，而未纹理化的函数则相反。 编辑：您可以使用此片段函数同时使用纹理颜色和顶点颜色：

fragment float4 fragment_func_blended(Vertex vert [[stage_in]],
                                      texture2d<float>  tex2D     [[ texture(0) ]],
                                      sampler           sampler2D [[ sampler(0) ]]) {
    // texture color
    float4 texture_sample = tex2D.sample(sampler2D, float2(vert.texCoord[0],vert.texCoord[1]));
    // vertex color
    float4 vertex_sample = vert.color;
    // Blend the two together
    float4 blended = texture_sample * vertex_sample;

    // Or use another blending operation.
    // float4 blended = mix(texture_sample, vertex_sample, mix_factor);
    // Where mix_factor is in the range 0.0 to 1.0.
    return blended;

}