make box-mode point cloud voxels render lighter on top than bottom #1058

codebot · 2023-09-07T01:20:19Z

Previously, the GLSL 1.2 shader for box-mode rendering of point clouds resulted in the top of the voxels rendering darker than the bottoms of the voxels. I think it looks nicer the other way around (top lighter than bottom), since most scenes are lit from the top.

(The GLSL 1.2 program is being used because of #851 ; the GLSL 1.5 shaders calculate lightness differently.)

Strangely, this GLSL 1.2 shader program structure has been in rviz for at least 11 years (according to git-blame). Am I just using it incorrectly, or have the tops of voxels always been darker than the bottoms of voxels, when rendering point clouds as boxes?

It may be important to note that I'm using a machine with an integrated (Intel) GPU. I don't have access to a machine with a discrete GPU to test the behavior in that case, since I assume a different shader program is selected when a GPU is present. It would be interesting to know if the same behavior happens with a GPU.

To see the effect:

start a point cloud streaming from anything
add a point cloud visualizer to rviz
select "Boxes" style
rotate camera around to view the scene from above and below

ahcorde · 2023-09-07T10:09:43Z

can you share a gif ? I tried with my discrete GPU, but I can't see any difference

codebot · 2023-09-07T13:24:55Z

That's interesting! I guess the discrete GPU is doing the "real" lighting calculation, rather than the "fake-lighting" shading used in glsl120/nogp/box.frag. That explains why this issue has been in the code for so long, since I assume that most people using RViz heavily for point-cloud visualization have a discrete GPU in their machine.

I attached two GIFs of a stereo camera looking at a tabletop, reduced using the PCL voxel_grid filter and rendered in Boxes mode in rviz.

The first GIF shows the current behavior on "integrated GPU" machines, where the top of the voxels is darker than the bottom. This works fine, but just looks kind of weird because most scenes in the real world are lit from above.

The second GIF shows what it looks like using this PR, with the top-side brighter in the fake-lighting shader.

(Please ignore the dithering artifacts due to heavy compression in the GIFs, but at least they show the relative brightness)