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Second-Depth Anti-Aliasing
Sunday, August 28, 2011 | Permalink

Source code
SDAA.zip (1.3 MB)

Direct3D 10
Direct3D 10.1
This demo shows another anti-aliasing technique using the depth buffer and a second-depth buffer for locating the edges. First edges are deteced. Then for each edge pixel it is determined whether an edge is cutting through this pixel or not. There are essentially two types of edges in a scene: creases and silhouette edges. When there's a crease the distance to the edge can be found by sampling two neighbors to the left and two the right and computing the intersection point where they meet, and similarly vertically of course. For silhouette edges there's a gap in the depth values so this doesn't work. So we use a buffer of second-depth values for this case, i.e. the depths of the backfaces in the scene, and use the same logic with those values and compute the intersection point in the same fashion. Once the edges are found we blend with a neighbor pixel in the same fashion as in GPAA/GBAA.

This technique is less intrusive to the overall rendering and should be easier to integrate into an existing engine than GPAA/GBAA. The only addition is the second-depth buffer. If the engine already has a pre-Z pass this can be altered into a second-depth pass by switching to front-face culling. Depending on the scene this may turn out faster or slower than a regular pre-Z pass. In this demo second-depth is in fact faster.

On the downside, this technique requires that there indeed are backfaces behind edges. This means that thin objects, billboards/foliage etc., will not get antialiased unless extra backside geometry is added. Quality-wise it rivals that of GPAA/GBAA, but requires good precision in the depth buffer to work.

This demo should run on any DX10 capable GPU.