public void setProjectionMatrix(Matrix4f projMatrix) {
        if (projMatrix == null) {
            overrideProjection = false;
            projectionMatrixOverride.loadIdentity();
        } else {
            overrideProjection = true;
            projectionMatrixOverride.set(projMatrix);
        }
        updateViewProjection();
    }
Overrides the projection matrix used by the camera. Will
use the matrix for computing the view projection matrix as well.
Use null argument to return to normal functionality.

@param projMatrix the desired projection matrix (unaffected) or null
    to cease the override
jme3-core/src/main/java/com/jme3/renderer/Camera.java