How to scale a matrix obtained with glm::lookat()?

Question

I am trying to create an orthographic view (separate from the final perspective view). I know the view's scale, position, it's up vector, and the point it's looking at. So it seems easiest to simply use glm::lookAt() to create the view matrix, except there's no way to specify scale.

Is there a way to introduce scaling with glm::lookAt()? I don't think it's possible to scale the matrix made by lookAt, since scaling needs to happen first to get the 'expected' result (objects appearing larger or smaller, like zooming a camera in or out). I may be wrong there though.

If it's not possible while using lookAt, is there a series of glm functions that would be equivalent?

theoemms theoemms · Accepted Answer · 2015-02-11T16:24:46

In terms of matrix transformations, you can start with a scale and apply the glm::lookAt() matrix afterwards. I'm not familiar with glm, but I have used GLUT before. You should be able to do a matrix multiplication like this (I'm assuming that you've already transformed everything into scene space, defined all the variables etc.)


    TransformedVector = glm::lookAt(cameraPosition,
                                    cameraTarget,  
                                    upVector) * 
                        glm::scale(scalingFactor, 
                                  scalingFactor, 
                                  scalingFactor) * 
                        OriginalVector;

If this behaves peculiarly try swapping the glm::lookAt() and glm::scale() order.

How to scale a matrix obtained with glm::lookat()?

1 Answers