将SCNGeometryTessellator与使用自定义SCNProgram的SCNGeometry一起使用？
将SCNGeometryTessellator与使用自定义SCNProgram的SCNGeometry一起使用？
提问于 2021-05-06 13:13:28
我正在尝试将SCNGeometryTessellator添加到一些使用自定义SCNProgram的SceneKit几何体中。我的几何图形渲染正常，但我一添加SCNGeometryTessellator，就会看到以下错误：
[SceneKit] Error: Compiler error while building render pipeline state for node <C3DNode:0x1053e9700 "(null)"
geometry: <C3DParametricGeometry<Plane>:0x1053e9160 "(null)"
mesh: <C3DMesh 0x282590620 "(null)"
element0: <C3DMeshElement 0x2823922b0 type:triangles primCount:200 channels:1 indexBytes:2 offset:0 acmr:0.605000 inst:1 dataSize:1200 shared:0x0>
source position (channel:0) : <C3DMeshSource 0x2837fbbf0(position) data:(0x281009ce0) mut:0 count:121 type:float3 divisor:0 mtl:0 offset:0 stride:32>
source normal (channel:0) : <C3DMeshSource 0x2837fb480(normal) data:(0x281009ce0) mut:0 count:121 type:float3 divisor:0 mtl:0 offset:12 stride:32>
source texcoord (channel:0) : <C3DMeshSource 0x2837fbb80(texcoord) data:(0x281009ce0) mut:0 count:121 type:float2 divisor:0 mtl:0 offset:24 stride:32>
renderable element0: <C3DMeshElement 0x2823922b0 type:triangles primCount:200 channels:1 indexBytes:2 offset:0 acmr:0.605000 inst:1 dataSize:1200 shared:0x0>
renderable source position: <C3DMeshSource 0x2837fbbf0(position) data:(0x281009ce0) mut:0 count:121 type:float3 divisor:0 mtl:0 offset:0 stride:32>
renderable source normal: <C3DMeshSource 0x2837fb480(normal) data:(0x281009ce0) mut:0 count:121 type:float3 divisor:0 mtl:0 offset:12 stride:32>
renderable source texcoord: <C3DMeshSource 0x2837fbb80(texcoord) data:(0x281009ce0) mut:0 count:121 type:float2 divisor:0 mtl:0 offset:24 stride:32>
>
mat0: <C3DMaterial 0x2837159d0 : "(null)", custom <C3DFXTechnique>>
>
>:
Error Domain=AGXMetalA14 Code=3 "Attribute 0 incompatible with MTLStepFunctionPerPatchControlPoint." UserInfo={NSLocalizedDescription=Attribute 0 incompatible with MTLStepFunctionPerPatchControlPoint.}
[SceneKit] Error: _executeProgram - no pipeline state下面是我创建几何体的方法：
let program = SCNProgram()
program.vertexFunctionName = "myVertexShader"
program.fragmentFunctionName = "myFragmentShader"
let mat = SCNMaterial()
mat.program = previewProgram
let plane = SCNPlane()
plane.widthSegmentCount = 1
plane.heightSegmentCount = 1
plane.firstMaterial = mat
let tessellator = SCNGeometryTessellator()
tessellator.edgeTessellationFactor = 10.0
tessellator.insideTessellationFactor = 10.0
tessellator.smoothingMode = .pnTriangles
plane.tessellator = tessellator
// add plane node to scene...如果我移除自定义材质，则镶嵌器实际上可以工作，但我需要使用SCNProgram。
导致此错误的原因是什么?如何使用SCNGeometryTessellator
回答 1
Stack Overflow用户
回答已采纳
发布于 2021-05-06 13:13:28
添加tessellator和SCNGeometry后，SCNProgram需要使用细分后顶点函数，而不是标准顶点函数。我找到的唯一能涵盖这一点的文档是苹果的metal tessellation programming guide
虽然我不是一个金属镶嵌的期望值，但这是我对这个问题的理解：
假设您的正常顶点函数如下所示：
struct VertexInput {
float3 position [[attribute(SCNVertexSemanticPosition)]];
float3 normal [[attribute(SCNVertexSemanticNormal)]];
float2 texCoords [[attribute(SCNVertexSemanticTexcoord0)]];
};
vertex ColorInOut myVertexShader(VertexInput in [[ stage_in ]], ...) {
...
}有关Attribute 0 incompatible with MTLStepFunctionPerPatchControlPoint的错误说明您的输入类型(VertexInput)与当前渲染管道的预期顶点输入不匹配。这是因为添加细分后，渲染管道将更改为使用特殊的后期细分顶点函数，而不是标准顶点函数。
后期细分顶点函数从细分器处而不是从几何体中获取输入。这是上面的顶点着色器转换为后细分顶点函数：
struct PatchIn {
patch_control_point<VertexInput> control_points;
};
[[patch(triangle, 3)]]
vertex ColorInOut myVertexShader(PatchIn patchIn [[stage_in]],
float3 patch_coord [[ position_in_patch ]], ...)
{
// We have to compute the correct input positions from the tessellation data
// Note that there's probably a cleaner/better way to do this
// Barycentric coordinates
float u = patch_coord.x;
float v = patch_coord.y;
float w = patch_coord.z;
// Convert to cartesian coordinates
const float3 pos = float3(
u * patchIn.control_points[0].position.x + v * patchIn.control_points[1].position.x + w * patchIn.control_points[2].position.x,
u * patchIn.control_points[0].position.y + v * patchIn.control_points[1].position.y + w * patchIn.control_points[2].position.y,
u * patchIn.control_points[0].position.z + v * patchIn.control_points[1].position.z + w * patchIn.control_points[2].position.z);
...
}将折点函数重写为镶嵌后折点函数后，几何应使用镶嵌和自定义SCNProgram进行渲染
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/67412205
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