Optimising Scatterplot further

[JobLeonard]

This is low-priority, so I'll just write a checklist to get it out of my head so I can focus on other stuff.

• [x] pre-render points on separate small canvases once, then use them as sprites for faster drawing.
  • [x] since the colors palettes are stored as an array of strings, store sprites in an array with matching indices. When drawing just use index values to determine which bitmap to draw (removes need to loop once for every color and do a string comparison on every point each loop)
• [ ] similarly, pre-render text labels once and draw that (not likely to matter much)
• [x] make sure all draw calls are integer values
• [ ] create helper functions that takes care of the above
  • [ ] create helper class that holds a reference to the canvas that deals with this?

The first two points will make all the difference on mobile hardware, I suspect.

[JobLeonard]

Implemented