Could also be that calling a single line of mode 5 makes the entire screen to be 512x224, but again we are into the same theory league as who shot JFK...
I'm sorry, but this talk about the resolution of "the entire screen" shows that you don't seem to grok how a CRTC or for that matter a raster display works. A CRT only has a discrete "resolution" in the Y axis--the number of visible scanlines. The X "resolution" is merely a question of how rapidly the analog signal feeding the CRT changes, and there's absolutely no reason that frequency has to be the same on each scanline. You could theoretically make a CRTC that produced a 320-pixel horizontal resolution in the top half of the display, a 256-pixel horizontal resolution on odd-numbered scanlines in the bottom half, and an 800-pixel horizontal resolution on even-numbered scanlines in the bottom half. Of course this hypothetical CRTC would have no practical use whatsoever, but it would work perfectly fine with any standard unmodified CRT.
Of course, an
emulator has to ultimately produce a rectangular image with a discrete resolution in both axes. When the emulated CRTC output has different resolutions on different scanlines, the only way you can do this while preserving all the horizontal detail is by upscaling every scanline to the highest horizontal resolution that's present in the frame. The only other possibility is to
downscale the higher-resolution scanlines to the lower resolution. That's what your SD3 screenshot is doing, and it's not correct emulation--it's throwing away image detail that would be visible on real hardware.
Someone (Arbee? Aaron?) help me out here, I'm not sure if I'm getting through...
