View Full Version : GLM order of transforms

03-28-2012, 11:34 PM
I have an object which I first want to rotate (about it's own center) then translate it to some point. I have a glm::quat that holds the rotation and a glm::vec3 that holds the point to which it needs to be translated.

glm::vec3 position;
glm::quat orientation;
glm::mat4 modelmatrix; <-- want to combine them both in here

modelmatrix = glm::translate(glm::toMat4(orientation),position);

Then at my render function I do..

pvm = projectionMatrix*viewMatrix*modelmatrix;
glUniformMatrix4fv(pvmMatrixUniformLocation, 1, GL_FALSE, glm::value_ptr(pvm));

..and render...

Unfortunately the object just orbits around the origin when I apply a rotation (the farther the "position" from the origin, the larger the orbit).

When I apply only the position it translates fine. When I apply only the rotation it stays at the origin and rotates about it's center (as expected). So why does it go weird when I apply them both? Am I missing something basic?

thanks in advance,


03-29-2012, 01:57 AM
"pvm = projectionMatrix*viewMatrix*modelmatrix;"

You created a MVP matrix, not a PVM one... if this matter.

03-29-2012, 07:13 PM
I was under the impression that GLM::translate , translates the 1st argument based on the 2nd vector. Based on that assumption I thought I was creating a mat4 from the quaternion and then translating it (which is the correct order). That's not the case apparently.

Thanks groovounet for the suggestion on the pvm, you're right.

03-31-2012, 06:03 AM
glm::translate is equivalent to creating a translation matrix and multiplying this matrix by the one passed in parameter except that this operation is optimized.