opengl如何决定要使用的Mip级别? [英] How does opengl decide which mip level to use?

问题描述

这个问题很容易解释.我问的是使用可能来自任何地方的纹理坐标(均匀，变化，另一个纹理获取).

The question is fairly self explanatory. I'm asking in terms of using texture coordinates that could have come from anywhere (a uniform, a varying, another texture fetch).

例如，我对一个mipmapped(或各向异性过滤)的纹理进行纹理获取，并使用在顶点着色器中设置的变化的平方.我假设glsl无法确定像这样的任意复杂函数的导数，那么它怎么知道要使用哪个mip级别?

Say for example I do a texture fetch on a mipmapped (or anisotropically filtered) texture, and I use the square of a varying which was set in the vertex shader. I assume that glsl cannot determine the derivative of an arbitrarily complex function like this, so how does it know which mip level to use?

谢谢.

推荐答案

通常使用空间连贯性.它在至少2x2像素的块上计算相同的值，并计算相邻像素之间的离散差.对于导数而言，这就足够了.

It is usually using spatial coherence. It computes the same value on a block of at least 2x2 pixels, and computes the discrete difference between the neighbors. That's enough of an approximation for the derivative.

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