Vertex paint/weight paint is unusuable on dense meshes. Here's a solution.

When trying to edit vertex paint or weight paint on dense meshes, the responsiveness of the ui becomes slow and unusable, making it impossible to paint.

To fix this, the paint tools should modify the screen pixels rather than the mesh. The paint would stay applied to the screen pixels until either they click apply paint, exit painting mode, or they rotate the viewport, then the paint is transferred onto the underlying vertices of the mesh, making the painting process responsive regardless of the density of the underlying geometry.