I have managed to fix a few more bugs with the extended size sprites, as the following shots show. Apologies for the horrible quality of the images, my usual phone is not in reach, and the one I had on hand has a terrible camera.
First, here is a sprite with extended width (64 pixels wide) mode on, and extended height mode on, with a sprite height of 100 pixels. That's a big sprite! Sprite data addresses are still in multiples of 64 bytes, but can span upto 1KB for big sprites -- that's enough for 128 rows of unique data.
Here is another similar shot where I have changed the contents of screen memory (which is where I have the sprite pointed to for convenience) to show that it is noticing all 1KB of it:
In the previous post I spoke about adding "xray-mode" to mark foreground, background, sprite and border elements, so that I can debug the sprites more easily. This is what it looks like for this display. Looks like everything is getting correctly classified. A little after I took these screen shots, I realised that the sprite background/foreground priority bug seems to be fixed -- either that, or I have the sense of the flag backwards. In any case, the sprites are appearing behind the text, which proves that I can do the priority sorting. I just checked in VICE, and confirmed that I did indeed have the sprite priority flag working backwards -- so I'll add that to the next resynthesis run. This is a good discovery, because it means that a whole bunch of extra games should work now as well.
Here is the same sprite with horizontal tiling turned on, making it repeat across the screen every 64 pixels -- great for parallax background.
What didn't work was the bitplane modification mode, which I have poked around with a bit since, and hopefully will have working soon.