如何使用WebGL异步加载图像，创建纹理，渲染和保存图像？

I am attempting to write an application that uses very large textures. The idea is that you work on a scaled version of the texture in realtime modifying shaders and when finished the application would apply your changes to the original unscaled (large) texture. The problem is that profiling shows something like the following:I am attempting to write an application that us