Ideas for performance improvements

[iwbnwif]

These are rough notes. This issue will need to be updated or replaced.

1. Draw background to a bitmap (background colour, gradient, grid etc.) and then blit the bitmap rather than redrawing it each time. The background will only need to be redrawn on a scale or grid change.
2. Use wxDC (i.e. not wxGraphicsContext or wxGCDC) for drawing the background. The grid looks better non-antialiased anyway.
3. Draw text on wxDC rather than a graphics context. Drawing text on a graphics context double anti-aliases the text and it looks weird as well as being slower.
4. When dragging multiple objects, draw them onto a transparent bitmap and move the bitmap.
5. When scrolling, only draw the objects that are appearing on the page, the rest can be blitted.
6. Zooming, using a bitmap rather than a complete redraw ala Google maps, Visio etc.