Attempts at Apple2 Double-Lowres Programming

When I posted links to my SNES-style Mode7 routines, I had requests that I look into adding support for the not-very-commong Apple IIe Double Lores mode (80x40x15color).

This would halve the framerate, and also with page-flipping difficult (non-existent?) would be flickery. I thought I'd try anyway.

It is a bit hackish, but I'm drawing offscreen and copying in to avoid most of the flicker, and I've implemented 80x40 mode7 as well as sprite handling.

Downloads

Disk image: dlowres_mode7.dsk (140k)
Source code can be found in the github repository: You'll need cc65 to build it.
https://github.com/deater/dos33fsprogs/graphics/dgr/dlowres_mode7

Screenshots

Taken with AppleWin emulator, but looks similar on actual hardware.

Got everything working! Although a bit slowly. Left is 80x40 mode, right is the same scene at 40x40, see if you can tell the difference.

Reasonable results (the black line is the current line being drawn, in 40x40 mode this is hidden by the page flipping):

Results when I wasn't shifting the AUX color:

Forgot that I was writing to PAGE2 not just switching to PAGE2 so one of the $400 ranges was being left blank.

Initial attempt at setting the soft switches led to some crazy looking results:

Video

See the dlowres code in action in the middle of this video:

Development Log

6 December 2017

Got the 80x40 mode properly working, as well as sprite handling with updated higher-res sprites. Frame rate leaves something to be desired though.

6 December 2017 (early AM)

Figured out I need to rotate left the AUX colors for the NTSC artifacting to work out.

5 December 2017

Initial hacked-up double lo-res code, colors are all wrong.

To the TFV (Regular Lowres Mode7) Page

To my Apple2 Projects Page