#pragma fragmentoption ARB_precision_hint_fastest "+ Precision Hints (ARB_precision_hint_fastest, ARB_precision_hint_nicest)
Fragment program computations are carried out at an implementation-
dependent precision. However, some implementations may be able to perform
fragment program computations at more than one precision, and may be able
to trade off computation precision for performance.
If a fragment program specifies the "ARB_precision_hint_fastest" program
option, implementations should select precision to minimize program
execution time, with possibly reduced precision. If a fragment program
specifies the "ARB_precision_hint_nicest" program option, implementations
should maximize the precision, with possibly increased execution time.
Only one precision control option may be specified by any given fragment
program. A fragment program that specifies both the
"ARB_precision_hint_fastest" and "ARB_precision_hint_nicest" program
options will fail to load."
GLSL中纹理坐标Y方向的原点在顶部，而HLSL中纹理坐标Y方向的原点在底部，所以你需要使用这个公式uv.y = 1 – uv.y 对每个点重新定义纹理坐标。uv中的每一项和vertices中的每一项都是一一对应的
在unity中，UV坐标划分，分下面两大步骤
1. 参考的标准是，unity刚导入时的那张图，即原图
2. 原图的左下角uv坐标定为(0,0)，原图的右上角的uv坐标定位(1,1)，原图的其它任何一个位置按照比例都会有一个uv坐标，比如原图的左上角的uv坐标定位（0,1），原图的右下角的UV坐标定位（1,0），原图的中心（对角线的交点）位置为（0.5,0.5），等等
