As for the remainders, turns out they actually comprise the small/large saucer, 4 shrapnel (explosion) patterns, and one bitmap of the player ship at '0 degrees' rotation. Since there only appears to be a single function in the DVG ROM to display the saucer, I'm assuming that the global scale is used for the 2nd saucer - but I need to verify that.
But for now, I've added the large saucer and now I'm at the exact point where I left off the text version. But it's a good indication of how the final game will look on the IIGS. I'll likely retain the 256x192 display area, but center it on the IIGS 320x200 SHR display.
|All 3 sizes of asteroids and large saucer|
It should be straightforward to render the shrapnel patterns next. Although the DVG notes online suggest the global scaling factor may also be used for explosions, I can't see where that's the case when I run the arcade emulation, and certainly Norbert is not scaling them at all.
I think that just leaves the ship, shots and ship explosion. As I've mentioned in a previous entry, these (mostly) manifest themselves in the display list as component vectors, and it's not possible to differentiate the actual objects from them alone. Again, at this point I will need to decide how to optimise the process - either tokenising the display list or bypassing the list altogether.
I've also had a few more thoughts on the erasure. I'm thinking dirty rectangles is going to be easiest to implement and I'm hoping fast enough. Each time I render an object, I'll add the coordinates and dimensions of the bounding rectangle to a list. When it's time to wipe the frame, I'll iterate through the list and wipe the rectangles. After all, this is what Knight Lore did...