Sonntag, 2. März 2014

Skinned Skeletal Animation Tutorial with Source Code

Today I completed a skinned skeletal animation tutorial, which is very helpful if you are just about to start with game development.

Different from the other tutorials I found in the web, this one is very light weight ( < 800 lines for the main mesh & animation code ) and works well with most modeling environments.



It has the following properties / features:
  • GPU Skinning / Matrix Palette Skinning
  • Bump Mapping (automatic normal map generation)
  • Spheric environment mapping
  • Ogre XML Based
  • Shaders in GLSL
  • Visual Studio 2010
  • Select LOD level with F1..F5
It is ready to use, which means you can load and display the animated models in a few lines of code:
static Mesh halo("halo.material",//     required material file)
         "halo.mesh.xml",        //     required mesh file
         "halo.skeleton.xml");   // optional skeleton file

int idle = halo.animation.GetAnimationIndexOf("idle");

halo.animation.SetPose(idle, // animation id (2 animations are available)
              time_elapsed); // time in seconds

halo.Draw( vec3f(0,0,0),     // position
           vec3f(0,0,0),     // rotation
        0);                  // LOD level

Also getting a bone matrix to put a weapon in the hand of the player e.g. is very simple:
int index  = halo.animation.GetBoneIndexOf("joint1"); 
matrix44 m = halo.animation.bones[ index ].matrix;

Setting the arm joint individually for shooting a weapon e.g. works as follows:( press F6 in the demo )
// get the index
int index  = halo.animation.GetBoneIndexOf("joint2"); 

// get / modify / set the matrix
matrix44 m = halo.animation.bones[ index ].matrix;
m.y_component()=vec3f(0,1,0); // set the rotation to identity
halo.animation.bones[ index ].matrix=m;

// re-evaluate the child bones
loopi(0,halo.animation.bones[ index ].childs.size())
        halo.animation.bones[ index ].childs[i], // bone id
        halo.animation.animations[0],            // animation
        -1);                                     // key frame -1 means not use the animation

The workflow is as follows:
  • Design the Model in Maya/MAX/Blender/etc.
  • Export the model using the OgreExporter
  • Convert the model from Ogre binary to Ogre XML (batch file is included)
  • Load the model in the tutorial code
The Main Skinning in GLSL: 
The main skinning is done in the vertex shader and only requires a few lines. For the shader, the skinning weights are stored in the color information as 3 floats. The bone IDs are unpacked from the w coordinate of the position information. The bone matrixes are stored as simple matrix array..
uniform mat4 bones[100];
uniform int  use_skinning;
void main(void)
  mat4 mfinal = gl_ModelViewMatrix ;

  // skinning
    vec3 weights=;
    vec3 boneid = gl_Vertex.w * vec3( 1.0/128.0 , 1.0 , 128.0 );
    boneid = (boneid - floor(boneid))*128.0;

    mat4 mskin  = bones[int(boneid.x)]*weights.x+
    mfinal = mfinal * mskin;
  gl_Position = gl_ProjectionMatrix * mfinal * vec4(,1.0);
Animating Notes for Maya
For Maya, put all animations in one time-line and export them as separate animations.
Ogre Export
Tangents need to be exported as 4D, to include the handedness. The tutorial version does not generate the tangents in the shader as it is faster to read them from the memory.
Bump Mapping
For the Ogre Material file, the bump map needs to be added manually by hand using the texture_bump parameter as follows:
texture Texture\masterchief_base.tif
texture_bump Texture\masterchief_bump_DISPLACEMENT.bmp
Ambient Texture Map
Same here. For the Ogre Material file, the ambient map needs to be added manually by hand using the texture_ambient parameter.
Environment Mapping
Environment mapping can be switched on in the material file using the following parameter:
env_map spherical

Screenshot of the settings in the OGRE exporter for Maya:

Commands to convert the OGRE binary to XML with 5 LODs

..\ogre_xml_converter\OgreXMLConverter.exe halo.mesh tmp\tmp.xml
..\ogre_xml_converter\OgreXMLConverter.exe -l 5 tmp\tmp.xml tmp\tmp.mesh
..\ogre_xml_converter\OgreXMLConverter.exe tmp\tmp.mesh halo.mesh.xml
..\ogre_xml_converter\OgreXMLConverter.exe halo.skeleton halo.skeleton.xml

Summary of the Code Structure: 

 Main.h : 
  • Main code 
Mesh.h : 
  • Reads .mesh.xml & .material files
  • Animation is optional
  • If an animation is present, it is stored in the animation variable 
  • Per vertex, the following parameters are stored: position xyz, normal, texture UV, tangent, tangent handedness, 3x skin weight and 3x bone index.
  • Bones are stored in the vertex shader as matrix palette (100 bones max)
MeshAnimation.h : 
  • Reads .skeleton.xml 
  • Bones are stored in the bones array
  • Animations are stored as tracks of keyframes for each animated bone 
  • After reading the animation, it is resampled to 20 frames per second
  • To set an animation, the skeleton matrices are computed by traversing the structure
  • Afterwards, they are multiplied with the inverse skinning matrix before passing to the shader (could be precalculated)
  • Interpolation is linear so far - slerp could be added for better transitions.
Get the ZIP here [ Download Source & Binary Files ] . 
The skinned character is included as rigged Maya binary file & obj file.
You can find more free characters for example here.

31 Kommentare:

  1. Great stuff! Thank you! :)

  2. Super cool :d Thanks a bunch

  3. Great, glad to hear that !
    If you find any bugs/issues let me know.

  4. Could you please be a little more specific? Thanks!

  5. This looks really fantastic. Trying to run the solution file using VS 2010 under Windows 7. Getting "Unhandled exception at 0x00000000 in Animation.exe: 0xC0000005: Access violation reading location 0x00000000" at wglSwapIntervalEXT(0);
    I commented it out for debugging purposes and then got another Access violation like the first one at: glCreateShader(type); -- returns a handle of 0. Any suggestions appreciated.

  6. Does the compiled executable that is included work without problems ? Further, can you check if the shader text file is read properly ? Havent had this bug yet. You can also email me in case of further problems.

    1. I uninstalled and re-installed the display driver (where I believe all of the shader stuff happens in the OpenGL display driver) and that fixed it!
      I agree: Great stuff! Thank you! :)

  7. Can someone explain me what is the max boneId that could be stored this way? And how does it relate to 128.0 constant?

  8. In the code, three bone id's are encoded as one float. They are unpacked in the line
    vec3 boneid = gl_Vertex.w * vec3( 1.0/128.0 , 1.0 , 128.0 );
    The maximum is currently 100 bones. Using quaternions you could get 256 I guess

  9. Hi friend, thanks for yor working.
    Now, I cant using other character from: I download (have mesh) then using OgreXMLConverter to chage to xml.
    Then import mesh.xml and material to Project.
    But program error: out of vector
    I try something but get nothing.
    Cam you help me.

  10. If you can send me the converted file (xml+texture files), I can take a look

    1. Here is my mesh.xml is converted from OgreXMLConverter tools

  11. The reason is that the xml has 2 sets of UV coordinates. The loader only supports one UV set. If you remove the second set in Maya it should work.

  12. Very helpful. I won't pretend I understand all of it yet, though. I was looking at Ogre to use the Keyframe and Skeletal animation parts but it appeared I had to use the rendering system as well. Your sample is much more simple to where the rendering is straight OpenGL.

    Is there a performance increase if using OGL 3+ dumping the immediate mode calls (glBegin/glEnd)?

  13. Sure, if you apply batch rendering of the entire mesh it will definitely be faster. Since its a tutorial i tried to keep it simple however.

  14. "Since its a tutorial i tried to keep it simple however."
    No problem, I totally understand. I appreciate the simplicity. I think much of my problem is in understand how skeletal animation works in general. Any resources would be helpful. Ogre docs are a bit thin on the subject. I found a few things on the web but I am looking for "plain English" writeups. (Sorry nothing against German! :) )

  15. Dieser Kommentar wurde vom Autor entfernt.

  16. I'm building my own animation and i can't understand how you use gl functions in "mesh.h",when I try to do the same in my program, i get an error about all the gl functions in "mesh.h".

  17. Hello, this tutorial is great, I have ported it to linux.

    I am at my next step: exporting my blender character to ogre. However, I there is no LOD data in exported file, allthough I've set LOD to 5...

    I am using latest ogre exporter and blender 2.7.7

    1. I'm currently struggling porting it to Linux...

      Can you share your source code or at least indications?

  18. The Ogre exporter should generate the LOD. There is a batch file included to achieve this

  19. I'm having a issue with an assert error from vertex similar but I'm not finding what is wrong in my vertex data other then the 3d tangents instead of 4d which I just force the w to be 1. I've been unable to load any model other then the ones you supplied. this is the vertex data of a cube that i'm trying to load

    1. if (sscanf(line, " <tangent x=\"%f\" y=\"%f\" z=\"%f\"", &v.x, &v.y, &v.z) == 3) {
      vertices[tangent_id++].tangent = vec4f(v.x, v.y, v.z, 1);
      cout << line << endl;

    2. I didn't realize the order that the converter batch file was different from the output you got, must be because I used blender. Since the faces were at the bottom and not the top it was causing the issue so I figured this out finally....spent all night toying with it now the only issue is the texture isn't showing, only the bumpmap but I'll try to sort that myself. thanks for the great tutorial.

  20. i need the source so badly for reference can you update the link please ?

    1. The code is also on my github

  21. hi guys, orge use column major matrix, so why the matrix here use like row major matrix, for example:
    inline void _matrix44::translate(const _vector3& t) {
    M41 += t.x;
    M42 += t.y;
    M43 += t.z;}
    as i understand, column major matrix should like below:
    void _matrix44::translate(const _vector3& t) {
    M14 += t.x;
    M24 += t.y;
    M34 += t.z;

  22. ok, my mistake, row major, column major, both type matrix in memory layout is same. and c++ is row major, so the M41, M42, M43 should translate.
    in the matrix multi, row major is like : vector * matrix; column major is like: matrix * vector.

  23. impossible to get the donwload ?