Order-independent transparency with depth peeling

This sample implements an order-independent transparency (OIT) algorithm using depth peeling. It renders a single torus whose opacity can be controlled via the UI. It produces pixel-perfect results. It is based on the original paper from Cass Everitt.

The OIT algorithm consists of several gather passes followed by one combine pass.

Each gather pass renders one layer of transparent geometry. The first pass renders the first layer, the second pass the second layer, etc. The N^th layer consists of all the N^th fragments of each pixel when the fragments are ordered from front to back.

The combine pass is a screen-space operation. It merges the layer images from back to front to produce the final result.

The algorithm can produce pixel-perfect results, even with intersecting geometry. When there are more geometry layers than gather passes, the backmost layers get skipped, but the visual results stay stable (i.e. no flickering pixels).