Coherent layer peeling for transparent high-depth-complexity scenes

We present two new image space techniques for efficient rendering of transparent surfaces that exploit partial ordering in the scene geometry. The first technique, called hybrid layer peeling, combines unordered meshes with ordered meshes in an efficient way, and is ideal for scenes such as volumes with embedded transparent meshes. The second technique, called coherent layer peeling, efficiently detects and renders correctly sorted fragment sequences for a given pixel in one iteration, allowing for a smaller number of passes than traditional layer peeling for typical scenes. Although more expensive than hybrid layer peeling by a constant factor, coherent layer peeling applies to a broader class of scenes, including single meshes or collections of meshes. Coherent layer peeling does not require costly clipping or perfect sorting. However, the performance of the algorithm depends on the degree to which the data is sorted. At best, when the data is perfectly sorted, the algorithm renders a correct result in a single iteration. At worst, when the data is sorted in reverse order, the algorithm mimics the performance of layer peeling but with a higher cost per iteration. We conclude with a discussion of a modified form of coherent layer peeling designed for an idealized rasterization architecture that would match layer-peeling in the worst case, while still exploiting correctly sorted sequences when they are present.