我正在使用 Assimp 将带有动画的 FBX 模型(在 Blender 中创建)加载到我的 DirectX 12 游戏中,但是我遇到了游戏应用程序渲染的动画的一个非常令人沮丧的错误。
测试模型是一个简单的“旗杆”,包含四个骨骼,如下所示:
骨骼0 -> 骨骼1 -> 骨骼2 -> 骨骼3
当绕过关键帧动画时,模型在其静止姿势中正确渲染。
当动画仅通过根骨骼 (Bone0) 旋转模型时,模型也会正确渲染和动画。
但是,当导入在第一个关节(即 Bone1)处旋转的模型时,聚集在每个关节周围的顶点似乎“卡在”其原始位置,而“骨骼”周围的顶点似乎会跟随正确的动画.
结果是拉伸几何的蹩脚之字形,如下所示:
相反,该模型在其动画姿势结束时应类似于“六角扳手”形状,如 AssimpViewer 实用工具中呈现的相同模型所示:
由于模型在 AssimpViewer 中正确渲染,因此可以合理地假设 Blender 导出的 FBX 文件没有问题。然后我检查并确认“卡在”关节周围的顶点确实确实由游戏加载代码正确分配了它们的顶点权重。C++ 模型加载和动画代码基于流行的 OGLDev 教程:https ://ogldev.org/www/tutorial38/tutorial38.html
现在令人生气的是,由于 AssimpViewer 工具正确地渲染了模型动画,我还从该工具中复制了 SceneAnimator 和 AnimEvaluator 类,以通过该代码分支生成最终的骨骼变换......只是最终得到完全游戏中同样的曲折错误!
我有理由相信在初始化时找到骨骼层次结构没有任何问题,所以这里是遍历层次结构并在每帧插入关键帧的关键函数。
VOID Mesh::ReadNodeHeirarchy(FLOAT animationTime, CONST aiNode* pNode, CONST aiAnimation* pAnim, CONST aiMatrix4x4 parentTransform)
{
std::string nodeName(pNode->mName.data);
// nodeTransform is a relative transform to parent node space
aiMatrix4x4 nodeTransform = pNode->mTransformation;
CONST aiNodeAnim* pNodeAnim = FindNodeAnim(pAnim, nodeName);
if (pNodeAnim)
{
// Interpolate scaling and generate scaling transformation matrix
aiVector3D scaling(1.f, 1.f, 1.f);
CalcInterpolatedScaling(scaling, animationTime, pNodeAnim);
// Interpolate rotation and generate rotation transformation matrix
aiQuaternion rotationQ (1.f, 0.f, 0.f, 0.f);
CalcInterpolatedRotation(rotationQ, animationTime, pNodeAnim);
// Interpolate translation and generate translation transformation matrix
aiVector3D translat(0.f, 0.f, 0.f);
CalcInterpolatedPosition(translat, animationTime, pNodeAnim);
// build the SRT transform matrix
nodeTransform = aiMatrix4x4(rotationQ.GetMatrix());
nodeTransform.a1 *= scaling.x; nodeTransform.b1 *= scaling.x; nodeTransform.c1 *= scaling.x;
nodeTransform.a2 *= scaling.y; nodeTransform.b2 *= scaling.y; nodeTransform.c2 *= scaling.y;
nodeTransform.a3 *= scaling.z; nodeTransform.b3 *= scaling.z; nodeTransform.c3 *= scaling.z;
nodeTransform.a4 = translat.x; nodeTransform.b4 = translat.y; nodeTransform.c4 = translat.z;
}
aiMatrix4x4 globalTransform = parentTransform * nodeTransform;
if (m_boneMapping.find(nodeName) != m_boneMapping.end())
{
UINT boneIndex = m_boneMapping[nodeName];
// the global inverse transform returns us to mesh space!!!
m_boneInfo[boneIndex].FinalTransform = m_globalInverseTransform * globalTransform * m_boneInfo[boneIndex].BoneOffset;
//m_boneInfo[boneIndex].FinalTransform = m_boneInfo[boneIndex].BoneOffset * globalTransform * m_globalInverseTransform;
m_shaderTransforms[boneIndex] = aiMatrixToSimpleMatrix(m_boneInfo[boneIndex].FinalTransform);
}
for (UINT i = 0u; i < pNode->mNumChildren; i++)
{
ReadNodeHeirarchy(animationTime, pNode->mChildren[i], pAnim, globalTransform);
}
}
VOID Mesh::CalcInterpolatedRotation(aiQuaternion& out, FLOAT animationTime, CONST aiNodeAnim* pNodeAnim)
{
UINT rotationKeys = pNodeAnim->mNumRotationKeys;
// we need at least two values to interpolate...
if (rotationKeys == 1u)
{
CONST aiQuaternion& key = pNodeAnim->mRotationKeys[0u].mValue;
out = key;
return;
}
UINT rotationIndex = FindRotation(animationTime, pNodeAnim);
UINT nextRotationIndex = (rotationIndex + 1u) % rotationKeys;
assert(nextRotationIndex < rotationKeys);
CONST aiQuatKey& key = pNodeAnim->mRotationKeys[rotationIndex];
CONST aiQuatKey& nextKey = pNodeAnim->mRotationKeys[nextRotationIndex];
FLOAT deltaTime = FLOAT(nextKey.mTime) - FLOAT(key.mTime);
FLOAT factor = (animationTime - FLOAT(key.mTime)) / deltaTime;
assert(factor >= 0.f && factor <= 1.f);
aiQuaternion::Interpolate(out, key.mValue, nextKey.mValue, factor);
}
我刚刚在这里包含了旋转插值,因为缩放和平移函数是相同的。对于那些不知道的人,Assimp 的 aiMatrix4x4 类型遵循列向量数学约定,所以我没有弄乱原始矩阵乘法顺序。
关于我的代码和我采用的两个基于 Assimp 的代码分支之间的唯一偏差是要求使用此转换函数将最终转换从 aiMatrix4x4 类型转换为 DirectXTK SimpleMath 矩阵(实际上是 XMMATRIX):
Matrix Mesh::aiMatrixToSimpleMatrix(CONST aiMatrix4x4 m)
{
return Matrix
(m.a1, m.a2, m.a3, m.a4,
m.b1, m.b2, m.b3, m.b4,
m.c1, m.c2, m.c3, m.c4,
m.d1, m.d2, m.d3, m.d4);
}
由于 aiMatrix4x4 Assimp 矩阵的列向量方向,最终的骨骼变换不会转置以用于 HLSL 消耗。最终骨骼变换数组被传递到蒙皮顶点着色器常量缓冲区,如下所示。
commandList->SetPipelineState(m_psoForwardSkinned.Get()); // set PSO
// Update vertex shader with current bone transforms
CONST std::vector<Matrix> transforms = m_assimpModel.GetShaderTransforms();
VSBonePassConstants vsBoneConstants{};
for (UINT i = 0; i < m_assimpModel.GetNumBones(); i++)
{
// We do not transpose bone matrices for HLSL because the original
// Assimp matrices are column-vector matrices.
vsBoneConstants.boneTransforms[i] = transforms[i];
//vsBoneConstants.boneTransforms[i] = transforms[i].Transpose();
//vsBoneConstants.boneTransforms[i] = Matrix::Identity;
}
GraphicsResource vsBoneCB = m_graphicsMemory->AllocateConstant(vsBoneConstants);
vsPerObjects.gWorld = m_assimp_world.Transpose(); // vertex shader per object constant
vsPerObjectCB = m_graphicsMemory->AllocateConstant(vsPerObjects);
commandList->SetGraphicsRootConstantBufferView(RootParameterIndex::VSBoneConstantBuffer, vsBoneCB.GpuAddress());
commandList->SetGraphicsRootConstantBufferView(RootParameterIndex::VSPerObjConstBuffer, vsPerObjectCB.GpuAddress());
//commandList->SetGraphicsRootDescriptorTable(RootParameterIndex::ObjectSRV, m_shaderTextureHeap->GetGpuHandle(ShaderTexDescriptors::SuzanneDiffuse));
commandList->SetGraphicsRootDescriptorTable(RootParameterIndex::ObjectSRV, m_shaderTextureHeap->GetGpuHandle(ShaderTexDescriptors::DefaultDiffuse));
for (UINT i = 0; i < m_assimpModel.GetMeshSize(); i++)
{
commandList->IASetVertexBuffers(0u, 1u, &m_assimpModel.meshEntries[i].GetVertexBufferView());
commandList->IASetIndexBuffer(&m_assimpModel.meshEntries[i].GetIndexBufferView());
commandList->IASetPrimitiveTopology(D3D_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
commandList->DrawIndexedInstanced(m_assimpModel.meshEntries[i].GetIndexCount(), 1u, 0u, 0u, 0u);
}
请注意,我正在使用上述代码中 DirectXTK12 库中的图形资源内存管理帮助器对象。最后,这是我正在使用的蒙皮顶点着色器。
// Luna (2016) lighting model adapted from Moller
#define MAX_BONES 4
// vertex shader constant data that varies per object
cbuffer cbVSPerObject : register(b3)
{
float4x4 gWorld;
//float4x4 gTexTransform;
}
// vertex shader constant data that varies per frame
cbuffer cbVSPerFrame : register(b5)
{
float4x4 gViewProj;
float4x4 gShadowTransform;
}
// bone matrix constant data that varies per object
cbuffer cbVSBonesPerObject : register(b9)
{
float4x4 gBoneTransforms[MAX_BONES];
}
struct VertexIn
{
float3 posL : SV_POSITION;
float3 normalL : NORMAL;
float2 texCoord : TEXCOORD0;
float3 tangentU : TANGENT;
float4 boneWeights : BONEWEIGHT;
uint4 boneIndices : BONEINDEX;
};
struct VertexOut
{
float4 posH : SV_POSITION;
//float3 posW : POSITION;
float4 shadowPosH : POSITION0;
float3 posW : POSITION1;
float3 normalW : NORMAL;
float2 texCoord : TEXCOORD0;
float3 tangentW : TANGENT;
};
VertexOut VS_main(VertexIn vin)
{
VertexOut vout = (VertexOut)0.f;
// Perform vertex skinning.
// Ignore BoneWeights.w and instead calculate the last weight value
// to ensure all bone weights sum to unity.
float4 weights = vin.boneWeights;
//weights.w = 1.f - dot(weights.xyz, float3(1.f, 1.f, 1.f));
//float4 weights = { 0.f, 0.f, 0.f, 0.f };
//weights.x = vin.boneWeights.x;
//weights.y = vin.boneWeights.y;
//weights.z = vin.boneWeights.z;
weights.w = 1.f - (weights.x + weights.y + weights.z);
float4 localPos = float4(vin.posL, 1.f);
float3 localNrm = vin.normalL;
float3 localTan = vin.tangentU;
float3 objPos = mul(localPos, (float4x3)gBoneTransforms[vin.boneIndices.x]).xyz * weights.x;
objPos += mul(localPos, (float4x3)gBoneTransforms[vin.boneIndices.y]).xyz * weights.y;
objPos += mul(localPos, (float4x3)gBoneTransforms[vin.boneIndices.z]).xyz * weights.z;
objPos += mul(localPos, (float4x3)gBoneTransforms[vin.boneIndices.w]).xyz * weights.w;
float3 objNrm = mul(localNrm, (float3x3)gBoneTransforms[vin.boneIndices.x]) * weights.x;
objNrm += mul(localNrm, (float3x3)gBoneTransforms[vin.boneIndices.y]) * weights.y;
objNrm += mul(localNrm, (float3x3)gBoneTransforms[vin.boneIndices.z]) * weights.z;
objNrm += mul(localNrm, (float3x3)gBoneTransforms[vin.boneIndices.w]) * weights.w;
float3 objTan = mul(localTan, (float3x3)gBoneTransforms[vin.boneIndices.x]) * weights.x;
objTan += mul(localTan, (float3x3)gBoneTransforms[vin.boneIndices.y]) * weights.y;
objTan += mul(localTan, (float3x3)gBoneTransforms[vin.boneIndices.z]) * weights.z;
objTan += mul(localTan, (float3x3)gBoneTransforms[vin.boneIndices.w]) * weights.w;
vin.posL = objPos;
vin.normalL = objNrm;
vin.tangentU.xyz = objTan;
//vin.posL = posL;
//vin.normalL = normalL;
//vin.tangentU.xyz = tangentL;
// End vertex skinning
// transform to world space
float4 posW = mul(float4(vin.posL, 1.f), gWorld);
vout.posW = posW.xyz;
// assumes nonuniform scaling, otherwise needs inverse-transpose of world matrix
vout.normalW = mul(vin.normalL, (float3x3)gWorld);
vout.tangentW = mul(vin.tangentU, (float3x3)gWorld);
// transform to homogenous clip space
vout.posH = mul(posW, gViewProj);
// pass texcoords to pixel shader
vout.texCoord = vin.texCoord;
//float4 texC = mul(float4(vin.TexC, 0.0f, 1.0f), gTexTransform);
//vout.TexC = mul(texC, gMatTransform).xy;
// generate projective tex-coords to project shadow map onto scene
vout.shadowPosH = mul(posW, gShadowTransform);
return vout;
}
我在发布之前尝试的最后一些测试:
我使用从 Blender 导出的 Collada (DAE) 模型测试了代码,只是在 Win32 桌面应用程序中观察到相同的扭曲曲折。
我还确认加载模型的 aiScene 对象返回全局根变换的单位矩阵(也在 AssimpViewer 中验证)。
我已经盯着这段代码大约一个星期了,我快疯了!真的希望有人能发现我错过的东西。如果您需要更多代码或信息,请询问!