rewrite imgui

[yyc-git]

refer to 【Unity】UIElements 渲染细节，比NGUI/UGUI/FairyGUI好在哪？
Built for performance: the UIElements Renderer – Unite Copenhagen 2019

• abstract render, extract IRender

• support webgpu render
  one draw call;
  one vertex buffer;
  (only update changed vertices instead of all!)
  one uber shader(render pipeline);

• change to bdd, rescript

• firstly implement box

• support state
  dispatch state like react;
  can get which elements are changed by compare state!

  • use render command list with state for minor update???

• not render each frame, only trigger rerender if state change

• trigger event

• with skin, custom control

• Textures are automatically atlassed by default