在 OpenGL 的广告牌上查看这个相关的 stackoverflow 帖子 它引用了一个很不错的lighthouse3d教程。以下是该技术的要点:
void billboardCylindricalBegin(
float camX, float camY, float camZ,
float objPosX, float objPosY, float objPosZ) {
float lookAt[3],objToCamProj[3],upAux[3];
float modelview[16],angleCosine;
glPushMatrix();
// objToCamProj is the vector in world coordinates from the
// local origin to the camera projected in the XZ plane
objToCamProj[0] = camX - objPosX ;
objToCamProj[1] = 0;
objToCamProj[2] = camZ - objPosZ ;
// This is the original lookAt vector for the object
// in world coordinates
lookAt[0] = 0;
lookAt[1] = 0;
lookAt[2] = 1;
// normalize both vectors to get the cosine directly afterwards
mathsNormalize(objToCamProj);
// easy fix to determine wether the angle is negative or positive
// for positive angles upAux will be a vector pointing in the
// positive y direction, otherwise upAux will point downwards
// effectively reversing the rotation.
mathsCrossProduct(upAux,lookAt,objToCamProj);
// compute the angle
angleCosine = mathsInnerProduct(lookAt,objToCamProj);
// perform the rotation. The if statement is used for stability reasons
// if the lookAt and objToCamProj vectors are too close together then
// |angleCosine| could be bigger than 1 due to lack of precision
if ((angleCosine < 0.99990) && (angleCosine > -0.9999))
glRotatef(acos(angleCosine)*180/3.14,upAux[0], upAux[1], upAux[2]);
}