As expected the elongation on various horizontal plane can result from concatenation of matrices. given R the amount of elongation, H the height of a reflexion plane, and P the reflexion matrix for this plane:
PSTMat = P*XMMatrixScaling(1, R, 1)*XMMatrixTranslation(0, H*(1 - R), 0);
then concatenate PSTMat to the WorldMat of the object and the Scene ViewProj and use this during the reflexion map generation. In my shaders a fading effect is also added to vanish the object with the height.
for objects O GlobalMat = WorldMat*PSTMat*ViewProj;
A couple of screenshots in the figure show the result for A) R=1, B) R=2 qnd C) R=0.5. The rain comes from a simplified version of the NVidia rain demo. When used the reflexion map texcoords are "distorded" to give the ripples with an animated ripple normalmap and some random offset with a noisy normalmap to simulate the impacts of drops.
