Drawing seems to cause the screen elements to flicker

[jbmorley]

This is particularly pronounced in Tile Fall. It might be a Tile Fall bug, but we should investigate.

[tomsci]

Also very noticeable on the paddle in Super Breakout, in addition to the balls not redrawing right, which is probably #121

[tomsci]

The issue with Tile Fall can be explained by the fact that TBarInit is supposed to call gUPDATE OFF before it returns, and our impl isn't doing that. Having fixed that there is much less flicker in Tile Fall, and the remainder is probably just hidden (on the Series 5 R1 at least) by the crazy amount of persistence of the LCD panel.

Breakout is a whole different ball game however.

[tomsci]

Another cause of flicker was that gLOADBIT and a couple of other commands would always trigger the equivalent of a gUPDATE(). I partially fixed this in 7c522c2 after determining it wasn't actually necessary in a couple of those cases. It is still necessary in eg gCLOSE to ensure graphics ops that copy across drawables don't get orphaned. We could remove that too with enough cunningness but I'm not sure if it's actually causing any problems.