OpenGL ES2 骨骼动画

Question

"I try to learn skeletal animation so I have many misunderstands" 我有一个从 Blender 导出的非常简单的 JSON 格式文件，它有一个立方体和一个只旋转了 4 帧的骨骼，所以我加载了具有 4 个属性的 VBO，位置 vec4、正常 vec4、权重 vec2 和骨骼索引 vec2渲染正确，骨骼有 pos、rotq 和 scale，所以我使用以下函数创建骨骼的变换矩阵

public static float[] createMat4(float[] t, float[] r, float[] s) {
    float[] mat4 = new float[16];
    float[] T = new float[16];
    float[] R = new float[16];
    float[] S = new float[16];
    setIdentityM(T, 0);
    setIdentityM(R, 0);
    setIdentityM(S, 0);
    translateM(T, 0, t[0], t[1], t[2]);
    rotateM(R, 0, r[3], r[0], r[1], r[2]);
    scaleM(S, 0, s[0], s[1], s[2]);
    float[] temp = new float[16];
    multiplyMM(temp, 0, T, 0, R, 0);
    multiplyMM(mat4, 0, temp, 0, S, 0);
    return mat4;
}

所以我通过将绑定乘以它的逆来计算骨骼最终矩阵 "as I understand" 对于每一帧，我将该矩阵乘以关键帧矩阵，该矩阵也是我通过先前的方法从 pos、rotq 和scl，最后我通过 mat4[] uniform 将这些矩阵上传到 GPU，这就是顶点着色器

uniform mat4 modelview;
uniform mat4 projection;
uniform mat4 bones[BONES];  
uniform int animated;

attribute vec4 vertexPosition;
attribute vec4 vertexNormal;
attribute vec2 textureCoords;
attribute vec2 skinweight;
attribute vec2 skinindex;

varying vec2 vTextureCoords;
varying vec4 viewDir;
varying vec4 modelviewNormal;
varying mat4 mv;

void main() {
    mv=modelview;
    vec4 newVertex;
    vec4 newNormal;
    if(animated==1){
       int index;
       index=int(skinindex.x);
       newVertex += (bones[index] * vertexPosition  * skinweight.x) ;
       newNormal += (bones[index] * vertexPosition * skinweight.x) ;

       index=int(skinindex.y);
       newVertex += (bones[index] * vertexPosition * skinweight.y);
       newNormal += (bones[index]  * vertexNormal* skinweight.y);
   }
   else{
       newVertex=vertexPosition;
       newNormal=vertexNormal;
   }
   vec4 modelviewVertex=(modelview * newNormal);
   modelviewNormal = normalize(modelviewVertex);
   viewDir = normalize(-modelview*newVertex);  
   vTextureCoords = textureCoords;
   gl_Position = (projection * modelview )* vec4(newVertex.xyz, 1.0);
}

当渲染结果出乎意料时，一些面消失了并且顶点随机移动。

Answer 1

问题出在四元数旋转上，我用这个函数把四元数转成旋转矩阵

private static float[] quaternionToMatrix(float[] q) {
    float[] m = new float[16];
    final float xx = q[0] * q[0];
    final float xy = q[0] * q[1];
    final float xz = q[0] * q[2];
    final float xw = q[0] * q[3];
    final float yy = q[1] * q[1];
    final float yz = q[1] * q[2];
    final float yw = q[1] * q[3];
    final float zz = q[2] * q[2];
    final float zw = q[2] * q[3];
    m[0] = 1 - 2 * (yy + zz);
    m[1] = 2 * (xy - zw);
    m[2] = 2 * (xz + yw);
    m[3] = 0;
    m[4] = 2 * (xy + zw);
    m[5] = 1 - 2 * (xx + zz);
    m[6] = 2 * (yz - xw);
    m[7] = 0;
    m[8] = 2 * (xz - yw);
    m[9] = 2 * (yz + xw);
    m[10] = 1 - 2 * (xx + yy);
    m[11] = 0;
    m[12] = 0;
    m[13] = 0;
    m[14] = 0;
    m[15] = 1;
    return m;
}

终于搞定骨骼动画了

Answer 2

newVertex += (bones[index] * vertexPosition  * skinweight.x) ;
newNormal += (bones[index] * vertexPosition * skinweight.x) ;

我在两个未初始化的值上看到一个 += 赋值运算符。

OpenGL ES2 骨骼动画

OpenGL ES2 skeletal animation

android

opengl-es

keyframe

skeletal-animation