c++ - 翻译 Assimp 3D 模型也旋转

Question

我在使用 Assimp 加载的 OpenGL (C++) 中有一个 3D 模型。我需要在屏幕上移动这个模型(平移)，就像它始终在 X 轴和 Y 轴(无 Z 轴)上面向相机一样。这就像移动这个模型，就像它只是 2D 一样(当然，如果我旋转它，它也会显示 Z 轴)。

我的渲染函数是:

    camX = CamY = 0;  
    camZ = 5;  
    lookatX = lookatY = lookatZ = 0;  

    void C3DModel::render(void)  
    { 

        static float step = 0.0f;  
        setCamera(camX, camY, camZ, lookatX, lookatY, lookatZ);  
        translate(-3, 1, 0); // here is the issue . 
        scale(scaleFactor, scaleFactor, scaleFactor);  
        rotate(step, 0.0f, 1.0f, 0.0f); 
    }

    void C3DModel::translate(float x, float y, float z) 
    {

       float aux[16];

       setTranslationMatrix(aux, x, y, z);
       multMatrix(modelMatrix, aux);
       setModelMatrix();
   }

   void C3DModel::setTranslationMatrix(float *mat, float x, float y, float z)
   {

       setIdentityMatrix(mat, 4);
       mat[12] = x;
       mat[13] = y;
       mat[14] = z;
   }

   void C3DModel::setScaleMatrix(float *mat, float sx, float sy, float sz)
   {

       setIdentityMatrix(mat, 4);
       mat[0] = sx;
       mat[5] = sy;
       mat[10] = sz;
   }

   void C3DModel::setRotationMatrix(float *mat, float angle, float x, float y, float z)
   {
       float radAngle = DegToRad(angle);
       float co = cos(radAngle);
       float si = sin(radAngle);
       float x2 = x * x;
       float y2 = y * y;
       float z2 = z * z;

       mat[0] = x2 + (y2 + z2) * co;
       mat[4] = x * y * (1 - co) - z * si;
       mat[8] = x * z * (1 - co) + y * si;
       mat[12] = 0.0f;

       mat[1] = x * y * (1 - co) + z * si;
       mat[5] = y2 + (x2 + z2) * co;
       mat[9] = y * z * (1 - co) - x * si;
       mat[13] = 0.0f;

       mat[2] = x * z * (1 - co) - y * si;
       mat[6] = y * z * (1 - co) + x * si;
       mat[10] = z2 + (x2 + y2) * co;
       mat[14] = 0.0f;

       mat[3] = 0.0f;
       mat[7] = 0.0f;
       mat[11] = 0.0f;
       mat[15] = 1.0f;
   }


   void C3DModel::rotate(float angle, float x, float y, float z) 
   {

      float aux[16];

      setRotationMatrix(aux, angle, x, y, z);
      multMatrix(modelMatrix, aux);
      setModelMatrix();
  }

  void C3DModel::scale(float x, float y, float z)
  {
      float aux[16];

      setScaleMatrix(aux, x, y, z);
      multMatrix(modelMatrix, aux);
      setModelMatrix();
  }

  void C3DModel::setIdentityMatrix(float *mat, int size)
  {
     // fill matrix with 0s
     for (int i = 0; i < size * size; ++i)
         mat[i] = 0.0f;
     // fill diagonal with 1s
     for (int i = 0; i < size; ++i)
        mat[i + i * size] = 1.0f;
  }

  void C3DModel::multMatrix(float *a, float *b) 
  {

     float res[16];

     for (int i = 0; i < 4; ++i) 
     {
         for (int j = 0; j < 4; ++j) 
         {
             res[j * 4 + i] = 0.0f;
             for (int k = 0; k < 4; ++k) 
             {
                 res[j * 4 + i] += a[k * 4 + i] * b[j * 4 + k];
             }
         }
     }
     memcpy(a, res, 16 * sizeof(float));
  }

  void C3DModel::setModelMatrix() 
  {
      glBindBuffer(GL_UNIFORM_BUFFER, matricesUniBuffer);
      glBufferSubData(GL_UNIFORM_BUFFER, ModelMatrixOffset, MatrixSize, modelMatrix);
      glBindBuffer(GL_UNIFORM_BUFFER, 0);
 }

 void C3DModel::crossProduct(float *a, float *b, float *res) 
 {
     res[0] = a[1] * b[2] - b[1] * a[2];
     res[1] = a[2] * b[0] - b[2] * a[0];
     res[2] = a[0] * b[1] - b[0] * a[1];
 }

 // Normalize a vec3
 void C3DModel::normalize(float *a)
 {

     float mag = sqrt(a[0] * a[0] + a[1] * a[1] + a[2] * a[2]);
     a[0] /= mag;
     a[1] /= mag;
     a[2] /= mag;
 }

 void C3DModel::setCamera(float posX, float posY, float posZ, float lookAtX, float lookAtY, float lookAtZ) 
 {

     float dir[3], right[3], up[3];
     up[0] = 0.0f;  up[1] = 1.0f;   up[2] = 0.0f;
     dir[0] = (lookAtX - posX);
     dir[1] = (lookAtY - posY);
     dir[2] = (lookAtZ - posZ);
     normalize(dir);
     crossProduct(dir, up, right);
     normalize(right);
     crossProduct(right, dir, up);
     normalize(up);
     float viewMatrix[16], aux[16];
     viewMatrix[0] = right[0];
     viewMatrix[4] = right[1];
     viewMatrix[8] = right[2];
     viewMatrix[12] = 0.0f;
     viewMatrix[1] = up[0];
     viewMatrix[5] = up[1];
     viewMatrix[9] = up[2];
     viewMatrix[13] = 0.0f;
     viewMatrix[2] = -dir[0];
     viewMatrix[6] = -dir[1];
     viewMatrix[10] = -dir[2];
     viewMatrix[14] = 0.0f;
     viewMatrix[3] = 0.0f;
     viewMatrix[7] = 0.0f;
     viewMatrix[11] = 0.0f;
     viewMatrix[15] = 1.0f;
     setTranslationMatrix(aux, -posX, -posY, -posZ);
     multMatrix(viewMatrix, aux);
     glBindBuffer(GL_UNIFORM_BUFFER, matricesUniBuffer);
     glBufferSubData(GL_UNIFORM_BUFFER, ViewMatrixOffset, MatrixSize, viewMatrix);
     glBindBuffer(GL_UNIFORM_BUFFER, 0);
 }

Answer 1

我将尝试在 2 个不同的矩阵中分离对象的旋转和平移请求的屏幕位置。

在每一帧，我会用 C3DModel::setRotationMatrix 中的代码计算旋转矩阵，用 C3DModel::setTranslationMatrix 计算平移，将它们组合成一个新的新模型矩阵并将其应用于您的对象。请记住，顺序很重要，如果您先旋转，对象将围绕您的 obj 文件中的原点旋转，如果您在平移之后旋转，它将围绕世界原点旋转(就像行星围绕太阳，太阳就是原点)。

最后，它看起来像:

void C3DModel::render(void){

    float* rotation = createRotation(angle, x, y, z);
    float* translation = createTranslation(x, y, z);
    float* updatedModel = mul(rotation, translation) //order matters
    setModel(updatedModel);
}