Alpha to coverage

Alpha to coverage

In the game, a polygonal model with translucent information textures is often used to simulate complex objects, such as grass, leaves, barbed wire, etc. If a real model is used, a grass with uneven edges may consume hundreds of polygons, but with a transparent texture, it can be solved with just two or three polygons.

However, when using such a texture with translucent information, unsightly jagged edges often appear on the boundary lines of its opaque and transparent parts. This problem can be solved by using the semitransparent blending technique, but it is necessary to draw all such objects in the scene in the order from far to near to ensure that their occlusion is correct, which puts a lot of pressure on the CPU and is undesirable. In previous versions of DirectX, Alpha testing and blending was simply a nightmare for graphic programmers.

In DirectX 10, a new technique is used called the alpha to coverage. Using this technique, texture pixels at the transparent and opaque junctions are sampled in a multipole manner (multi-sample) to achieve anti-aliasing effects. This solves this problem simply and effectively without introducing a large performance overhead. Outdoor scenes of the game will greatly benefit from this technology, leaves, barbed wire, grass edge will be more soft, smooth.

Related information:

Http://www.zwqxin.com/archives/opengl/talk-about-alpha-to-coverage.html

http://www.zhihu.com/question/25822656

http://www.zhihu.com/question/35725024

Alpha to coverage