使用 initWithVertexBuffers 编程生成 MDLMesh 对象

Question

如果您使用的是 iOS Metal，并且您有自定义的编程对象模型，并且（像我一样）您的模型随着 Metal2 和 iOS 11 的出现而停止工作，那么您可能已经开始研究如何以编程方式生成 MDLMesh。

Apple 文档说：“通常，您可以通过遍历 MDLAsset 对象的对象层次结构来获取网格，但您也可以从自己的顶点数据创建网格或创建参数化网格。” 不幸的是，它没有提供说明或示例代码。

您很快就会找到两个 MDLMesh 初始化调用，initWithVertexBuffer 和 initWithVertexBuffers。就像您在网上找不到示例代码或讨论一样快……至少我没有成功找到任何示例代码。

由于对于这个不经意的观察者来说应该如何完成并不是很明显，因此请求代码示例。

Answer 1

有很多示例使用工厂参数化方法之一创建 MDLMesh，例如立方体：

[MDLMesh newBoxWithDimensions:...

使用其中最简单的方法，对于“平面”（矩形），我生成了一个具有最少顶点数的 1x1 矩形：

MDLMesh *mdlMesh = [MDLMesh newPlaneWithDimensions:(vector_float2){1.0, 1.0}
                                          segments:(vector_uint2){1, 1}
                                      geometryType:MDLGeometryTypeTriangles
                                         allocator:metalAllocator];

然后我使用 Xcode 调试器来研究生成的 MDLMesh 是什么样子，以此来指导我创建一个更简单的对象，一个程序化的等边三角形。

以下代码对我有用。我相信比我更了解 Metal 的人可以提供更好的解决方案。但这有望让你开始，在一些正确的方向上......

所以直到有一个新的工厂参数方法

[MDLMesh newEquilateralTriangleWithEdgeLength:...

以下代码似乎可以解决问题...

static const float equilateralTriangleVertexData[] =
{
      0.000000,  0.577350,  0.0,
     -0.500000, -0.288675,  0.0,
      0.500000, -0.288675,  0.0,
};

static const vector_float3 equilateralTriangleVertexNormalsData[] =
{
    { 0.0,  0.0,  1.0 },
    { 0.0,  0.0,  1.0 },
    { 0.0,  0.0,  1.0 },
};

static const vector_float2 equilateralTriangleVertexTexData[] =
{
    { 0.50, 1.00 },
    { 0.00, 0.00 },
    { 1.00, 0.00 },
};

int numVertices = 3;

int lenBufferForVertices_position          = sizeof(equilateralTriangleVertexData);
int lenBufferForVertices_normal            = numVertices * sizeof(vector_float3);
int lenBufferForVertices_textureCoordinate = numVertices * sizeof(vector_float2);

MTKMeshBuffer *mtkMeshBufferForVertices_position          = (MTKMeshBuffer *)[metalAllocator newBuffer:lenBufferForVertices_position          type:MDLMeshBufferTypeVertex];
MTKMeshBuffer *mtkMeshBufferForVertices_normal            = (MTKMeshBuffer *)[metalAllocator newBuffer:lenBufferForVertices_normal            type:MDLMeshBufferTypeVertex];
MTKMeshBuffer *mtkMeshBufferForVertices_textureCoordinate = (MTKMeshBuffer *)[metalAllocator newBuffer:lenBufferForVertices_textureCoordinate type:MDLMeshBufferTypeVertex];

// Now fill the Vertex buffers with vertices.

NSData *nsData_position          = [NSData dataWithBytes:equilateralTriangleVertexData        length:lenBufferForVertices_position];
NSData *nsData_normal            = [NSData dataWithBytes:equilateralTriangleVertexNormalsData length:lenBufferForVertices_normal];
NSData *nsData_textureCoordinate = [NSData dataWithBytes:equilateralTriangleVertexTexData     length:lenBufferForVertices_textureCoordinate];

[mtkMeshBufferForVertices_position          fillData:nsData_position          offset:0];
[mtkMeshBufferForVertices_normal            fillData:nsData_normal            offset:0];
[mtkMeshBufferForVertices_textureCoordinate fillData:nsData_textureCoordinate offset:0];

NSArray <id<MDLMeshBuffer>> *arrayOfMeshBuffers = [NSArray arrayWithObjects:mtkMeshBufferForVertices_position, mtkMeshBufferForVertices_normal, mtkMeshBufferForVertices_textureCoordinate, nil];

static uint16_t indices[] =
{
    0,  1,  2,
};

int numIndices = 3;

int lenBufferForIndices = numIndices * sizeof(uint16_t);
MTKMeshBuffer *mtkMeshBufferForIndices = (MTKMeshBuffer *)[metalAllocator newBuffer:lenBufferForIndices type:MDLMeshBufferTypeIndex];

NSData *nsData_indices = [NSData dataWithBytes:indices length:lenBufferForIndices];
[mtkMeshBufferForIndices fillData:nsData_indices offset:0];

MDLScatteringFunction *scatteringFunction = [MDLPhysicallyPlausibleScatteringFunction new];
MDLMaterial *material = [[MDLMaterial alloc] initWithName:@"plausibleMaterial" scatteringFunction:scatteringFunction];

// Not allowed to create an MTKSubmesh directly, so feed an MDLSubmesh to an MDLMesh, and then use that to load an MTKMesh, which makes the MTKSubmesh from it.
MDLSubmesh *submesh = [[MDLSubmesh alloc] initWithName:@"summess" // Hackspeke for @"submesh"
                                           indexBuffer:mtkMeshBufferForIndices 
                                            indexCount:numIndices 
                                             indexType:MDLIndexBitDepthUInt16 
                                          geometryType:MDLGeometryTypeTriangles 
                                              material:material];

NSArray <MDLSubmesh *> *arrayOfSubmeshes = [NSArray arrayWithObjects:submesh, nil];

MDLMesh *mdlMesh = [[MDLMesh alloc] initWithVertexBuffers:arrayOfMeshBuffers
                                              vertexCount:numVertices
                                               descriptor:mdlVertexDescriptor
                                                submeshes:arrayOfSubmeshes];