Exploring ways to mipmap alpha-tested textures | lisyarus blog
In my village building game I'm using alpha-tested transparency for foliage — trees, bushes, grass, etc. This works simply by discarding (i.e. not drawing) any pixels having an alpha value of less than 0.5, and keeping the others. This is much cheaper than proper transparency, which requires sorting objects or pixels by distance to camera. Here's what it looks like:
Naturally, we want these textures to have mipmaps, for the same reasons as usual: to prevent aliasing, to improve texture cache utilization, etc. But there is a problem.
Let us have a look at the same fern from a large distance. Though, it will be too small to notice anything, so let's instead pretend that we're far away and bias the mipmap selection in the shader. Specifically, I'll use WGSL's textureSampleBias function to shift the selected mipmap level by 4. And here's the result:
It looks kinda round, instead of being pointy like before. Somewhat hilariously, the shadows are still correct, since I didn't add the biasing to the shadow map shader.
