我们使用同一个vertex shader来渲染之前描述的所有2D footprint。首先，对于给定的footprint坐标(x,y)来说，shader通过简单的缩放和变换来计算它的世界坐标(x,y)。接下来，从顶点纹理中读取高度值z。这里不需要任何过滤器，因为顶点和纹理采样是一一对应的-we use with a vertex shader to exaggerate the descr iption before all 2D footprint. First, the footprint to the coordinates (x, y), the shader by simple scaling and transform to calculate its world coordinates (x, y). Next, from the vertex texture read height z values. This does not require any filters, because vertex and texture sampling is one-to-one