My success in getting the initial 16-bit support into the backend, and getting it to work with resources from freddicove, triggered Kirben into a frenzy of updates to the Scumm engine code. 16-bit HE games seem to be working almost perfectly, now.
During this period, I have been doing some bug hunting in regard to this.
For example, when Kirben first mentioned strange graphical glitches occuring in the intro to freddicove, I started msvc debugger and traced the issue to an error in the SDL copyRectToScreen method, that I had failed to correct when changing to 16-bit — when testing for the special case of a rectangle being the full width of the screen, it checked the rectangle’s pitch (or number of bytes from the start of one line to the start of the next), instead of width (or number of pixels from the start of one line to the start of the next) for equality with the screen width, resulting in the case being used when the rectangle being copied was half the screen width, but not when it was full.
I then corrected this error, and began looking at similar glitches that had been reported in baseball2001, and spyfox3.
During this time, the full versions of Spy Fox 3, Backyard Soccer MLS, Freddi Fish 5: The Case of Coral Cove, and Moonbase Commander arrived from ebay, and I began using those for testing. So far, I have concentrated primarily on Spy Fox 3, as it seemed to have the highest instance of graphical errors.
Long story short: Kirben seems to have fixed all of the known display errors that were internal to the Scumm engine, and I now have cursors displaying in 16-bit, because the work he did fixing hePalettes to work properly in 16-bit was incompatible with the cursors rendering properly in 8-bit mode. (I have screenshots of this, but this post is cluttered as it is, and little, if any, difference is visible from those cursors rendering properly in 8-bit.)
Additionally because of all these rapid developments on the scumm engine, I will begin discussion and work on the API as soon as Sev gets back from his vacation.