Overlay anti-aliasing:
Most of the overlays are wires which causes a lot of flickering in motions due to aliasing problems.
Our goal is to have a technique that works with single sample per pixel to avoid extra cost of managing MSAA or additional texture buffers and jitters.
To solve this we use a simple and effective post-process AA. The technique goes like this:
- During wireframe rendering, we output the line color, the line direction and the distance from the line for the pixel center.
- Then, in a post process pass, for each pixels we gather all lines in a search area that could cover (even partially) the center pixel. We compute the coverage of each line and do a sorted alpha compositing of them.
This technique has one major shortcoming compared to MSAA:
- It handles (initial) partial visibility poorly (because of single sample). This makes overlapping / crossing wires a bit too thin at their intersection. Wireframe meshes overlaid over solid meshes can have half of the edge missing due to z-fighting (this has workaround). Another manifestation of this, is flickering of really dense wireframe if using small line thickness (also has workaround).
The pros of this approach are many:
- Works without geometry shader.
- Can inflate line thickness.
- Coverage is very close to perfect and can even be filtered (Blackman-Harris, gaussian).
- Wires can "bleed" / overlap non-line objects since the filter is in screen-space.
- Only uses one additional lightweight full-screen buffer (compared to MSAA/SMAA).
- No convergence time (compared to TAA).
Definition in file overlay_next_antialiasing.hh.
