C OpenGL Quaternion for Camera翻转它

首先,我们需要一种从角度和轴构造四元数的方法,我碰巧在pastebin上有这个,角度输入是弧度：

http://pastebin.com/vLcx4Qqh

确保你没有输入轴(0,0),这没有任何意义.

现在是实际的更新方法,我们需要让四元数从默认方向旋转相机指向目标点.请注意我刚刚写了这篇文章,它可能需要一些调试,可能需要一些优化,但这至少应该给你一个正确的方向.

void camera::update()
{
    // First get the direction from the camera's position to the target point
    vec3 lookAtDir = m_targetPoint - m_position;

    // I'm going to divide the vector into two 'components',the Y axis rotation
    // and the Up/Down rotation,like a regular camera would work.

    // First to calculate the rotation around the Y axis,so we zero out the y
    // component:
    vec3 lookAtHorizontal = vec3(lookAtDir.x,lookAtDir.z).normalize();

    // Get the quaternion from 'default' direction to the horizontal direction
    // In this case,'default' direction is along the -z axis,like most OpenGL
    // programs. Make sure the projection matrix works according to this.
    float angle = acos(vec3(0.0f,-1.0f).dot(lookAtHorizontal));
    quaternion horizontalOrient(angle,vec3(0.0f,0.0f));

    // Since we already stripped the Y component,we can simply get the up/down
    // rotation from it as well.
    angle = acos(lookAtDir.normalize().dot(lookAtHorizontal));
    if(angle) horizontalOrient *= quaternion(angle,lookAtDir.cross(lookAtHorizontal));

    // ...
    m_orientation = horizontalOrient;
}

现在实际上采用m_orientation和m_position来获取世界 – >相机矩阵

// First inverse each element (-position and inverse the quaternion),// the position is rotated since the position within a matrix is 'added' last
// to the output vector,so it needs to account for rotation of the space.
mat3 rotationMatrix = m_orientation.inverse().toMatrix();
vec3 inverseTranslate = rotationMatrix * -m_position; // Note the minus

mat4 matrix = mat3; // just means the matrix is expanded,the last entry (bottom right of the matrix) is a 1.0f like an identity matrix would be.

// This bit is row-major in my case,you just need to set the translation of the matrix.
matrix[3] = inverseTranslate.x;
matrix[7] = inverseTranslate.y;
matrix[11] = inverseTranslate.z;

编辑我认为它应该是显而易见的,但只是为了完整性,.dot()采用向量的点积,.cross()采用叉积,执行方法的对象是向量A,方法的参数是向量B.