render optimization

[wjian23]

currently, the render is implemented rudely.
problem:
1. no matter what the area is, we repaint all the view areas.
2. to deal with text and curve-line, we use wgpu with anti_aliasing, causing the amount of computation and memory space required 4 ～ 5 times than normal.

some ideas for improvement:
1. specify the dirty area when rendering
2. reduce the anti_aliasing scenes, cache the text glyph image or use cpu to render for text instead.
3. avoid painting the whole area once, split the area into little areas, then even with anti_aliasing will not occupy so much memory space.