给定一个方向和一个 position 如何用 GLM 计算旋转矩阵

Question

I am tying get a model matrix calculated that can be passed on to shaders. But i cannot figure out how to calculate the rotation portion of the matrix. I have two vectors: one a position and a facing direction one, here is the code:

glm::mat4x4 CalcModelMatrix( const glm::vec3& position, const glm::vec3& orientation )
{
  glm::mat4x4 model( 1.f );

  // displacement
  model = glm::translate( model, position );

  // rotation
  // ... 

  // scaling 
  model = glm::scale( model, glm::vec3( 1.f ) );

  return model;
}

I tried using std::atan2 to calculate component wise angles and apply those one after an other and glm::lookAt with a calculated up vector but I can't figure it out.

Answer 1

With euler you'll suffer. You neeed to use quaternions

http://www.opengl-tutorial.org/intermediate-tutorials/tutorial-17-quaternions/

You need to build your quaternion according to your rotation needs and then you can switch that back to mat4 with mat4 RotationMatrix = quaternion::toMat4(quaternion); to achieve the full model matrix