An implementation of ShapeRep that attempts to cache and reuse the mask texture that is used to render the filled/stroked geometry. There is an artificial cap on the size of shapes that are considered for caching, so that we do not fill up VRAM with lots of large shape masks. The shape is considered for caching only when it is rendered a certain number of times with unchanging transform (ignoring the translation components) and geometry. This means that this class is good for caching static shapes that are either completely stationary or being translated. This class will also attempt to reuse a mask that corresponds to a completely different shape instance as long as the two shapes are equal and the transforms only differ by their translation components. This means that if you have 1000 Path nodes all with exactly the same geometry but with different translation factors, then we will only rasterize and cache a single mask texture and reuse it among all the Path nodes. (Of course, the fact that we reuse the same mask texture for different sub-pixel translation factors means we're knowingly being a bit sloppy, so when caching is enabled you may see some dancing at the shape edges for slowly animating translations, but otherwise will hopefully not be too noticeable.) The current implementation limits the size of the cache (512 pixels in each dimension, and 4 MB in total) so that it doesn't grow without bound. Space is granted on a first come first served basis.