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# [SOLVED] Skeletal animation rotation problems

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### #1EngineCoder  Members   -  Reputation: 246

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Posted 28 May 2010 - 07:49 AM

I'm trying to render COLLADA animation exported from Blender. My test animation moves a human's hand up and left. I got the basic skinning working fine, but the animation rotates to the wrong direction. The animation is split to 4 animations: translate, rotateX, rotateY and rotateZ. I assume that I must combine those values to form a key frame's joint matrix and I must multiply it with the joint's parent's world matrix and store the result to joint's world matrix. Here's some code: Methods from Mesh class:
/**
* Applies matrices to skeleton. Should start from the root node.
* Joint's world transformation is parent's world transformation * local trans.
**/
void applySkin( Joint* joint )
{
assert( joint );

for (size_t c = 0; c < joint->children.size(); ++c) {
Math::multiplyMatrix( joint->children[ c ].transform,
joint->worldTransform,
joint->children[ c ].worldTransform );
applySkin( &joint->children[ c ] );
}
}

// Replaces joint named "name"'s transform matrix with matrix. Should start searching from root.
void replaceJointMatrix( const std::string& name, Joint* j, float matrix[ 16 ] )
{
assert( j );
assert( matrix );

if (name == j->name) {
for (int i = 0; i < 16; ++i) {
j->transform[ i ] = matrix[ i ];
}
return;
}
else {
for (size_t c = 0; c < j->children.size(); ++c) {
replaceJointMatrix( name, &j->children[ c ], matrix );
}
}
}

// Animations change rotX, rotY, rotZ, posX, posY and posZ. From these values the new joint transform matrix is constructed.
void applyAnimation()
{
for (std::map< std::string, Animation >::iterator a = animations.begin(); a != animations.end(); ++a) {
// Skips this animation if it's not running.
if (a->second.stepStartTime == 0) { continue; }

// If true, proceed to the next time step.
if ((SDL_GetTicks() - a->second.stepStartTime) / 1000.0f >= a->second.input[ a->second.inputIndex ]) {
++a->second.inputIndex;
a->second.stepStartTime = SDL_GetTicks();
}
// If true, the animation is finished.
if (a->second.inputIndex == (int)a->second.input.size()) {
animations.erase( a->first );
continue;
}

Joint joint;
findJoint( a->second.joint, &skeleton[ 0 ], &joint );

float t = (SDL_GetTicks() - a->second.stepStartTime) / 1000.0f;
int ind = a->second.inputIndex;
t /= a->second.input[ ind ];

float animRotationMatrix[ 16 ];
Math::identityMatrix( animRotationMatrix );

if (a->second.operation == "translate") {
float xv = (a->second.output[ ind - 1 == -1? 0 : (ind - 1)*3+0 ]);
posX = interpolate( xv, a->second.output[ ind * 3 + 0 ], t );

float yv = (a->second.output[ ind - 1 == -1? 1 : (ind - 1)*3+1 ]);
posY = interpolate( yv, a->second.output[ ind * 3 + 1 ], t );

float zv = (a->second.output[ ind - 1 == -1? 2 : (ind - 1)*3+2 ]);
posZ = interpolate( zv, a->second.output[ ind * 3 + 2 ], t );

Math::makeRotationMatrix4x4( animRotationMatrix, rotX, rotY, rotZ );
float transMatrix[ 16 ];
Math::identityMatrix( transMatrix );
transMatrix[ 3 ] = posX;
transMatrix[ 7 ] = posY;
transMatrix[11 ] = posZ;

Math::multiplyMatrix( transMatrix, animRotationMatrix, animRotationMatrix );
replaceJointMatrix( a->second.joint, &skeleton[ 0 ],
animRotationMatrix );
}
// Output values are changing X angle.
if (a->second.operation == "rotateX.ANGLE") {
float val1 = a->second.output[ ind - 1 == -1? 0 : ind - 1 ];
float val2 = a->second.output[ ind ];

rotX = interpolate( val1, val2, t );
Math::makeRotationMatrix4x4( animRotationMatrix, rotX, rotY, rotZ );
float transMatrix[ 16 ];
Math::identityMatrix( transMatrix );
transMatrix[ 3 ] = posX;
transMatrix[ 7 ] = posY;
transMatrix[11 ] = posZ;

Math::multiplyMatrix( transMatrix, animRotationMatrix, animRotationMatrix );

replaceJointMatrix( a->second.joint, &skeleton[ 0 ],
animRotationMatrix );
}

// Y and Z-angles are changed the same way, no need to paste them here.

vertexDeformed.clear();

applySkin( &skeleton[ 0 ] );

// Applies the deform.
// From COLLADA spec: outv = sum{ (v * BSM) * IBMi * JMi * JW }
for (size_t v = 0; v < influences.size(); ++v) {
Influence& i = influences[ v ];
vertexDeformed.push_back( Vector() );
Vector4 temp;
Vector4 v4 = Vector4( vertex[ v ].x, vertex[ v ].y, vertex[ v ].z, 1.0f );
Math::vectorMultMatrix4x4( v4, bindShapeMatrix, &temp ); // v * BSM

for (size_t j = 0; j < i.jointIndices.size(); ++j) {
// Finds a joint for this influence.
std::string jointName = jointArray[ i.jointIndices[ j ] ];
Joint joint;
findJoint( jointName, &skeleton[ 0 ], &joint );
Vector4 temp2;
Math::vectorMultMatrix4x4( temp, joint.ibm, &temp2 ); // * IBMi

Vector4 temp3;
Math::vectorMultMatrix4x4( temp2, joint.worldTransform, &temp3 ); // * JMi

temp3 *= weights[ i.weightIndices[ j ] ]; // * JW
vertexDeformed.back() += Vector( temp3.x, temp3.y, temp3.z ); // outv
}
}
}


I noticed that if I manually change a joint's translation (joint.transform[3, 7 and 11] ) nothing seems to change. From the rendered animation I think that my animation's pivot point is wrong. edit: I solved this problem. Solution in the last post. [Edited by - EngineCoder on May 29, 2010 6:33:16 AM]

### #2karwosts  Members   -  Reputation: 840

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Posted 28 May 2010 - 08:00 AM

Does your game use the same coordinate system as blender? (Up:Z Right:X Out:+Y)

You might try to describe the situation more specifically than "it rotates in the wrong direction", that's kind of vague.

### #3EngineCoder  Members   -  Reputation: 246

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Posted 28 May 2010 - 08:28 AM

Quote:
 Original post by karwostsDoes your game use the same coordinate system as blender? (Up:Z Right:X Out:+Y)You might try to describe the situation more specifically than "it rotates in the wrong direction", that's kind of vague.

My code uses Y-up, but swapping Y and Z in the rotation code does not make it right. Also I have checked Y-up in Blender's armature properties.

I'll post some screenshots tomorrow to describe how it looks and how it should look.

### #4EngineCoder  Members   -  Reputation: 246

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Posted 29 May 2010 - 12:19 AM

I finally got it working, after trying to find the problem for a week! I had to transpose the matrices that came with the COLLADA file and I had to use negative rotation angles.

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