Emulations (running on Linux/Unix/Windows/macOS, utilizing SDL2) of some - mainly - 8 bit machines, including the Commodore LCD, Commodore 65, and the MEGA65 as well.
PolyMega intro seems to produce(d) empty screen on Xemu. Initial guess was a DMA problem, but it turned out to be a glyph-trimming issue. It's a bit unclear for now, if it's not problematic on MEGA65 either (ie, compared to the document at least!).
It seemed, that the bit3 stuff is mostly ignored by MEGA65 even if it's in contradict with the documentation. This change fixed PolyMega to also work on Xemu/MEGA65.
This, it should be tested, if it's really OK in all cases for now. Also there are at least one trimming related other issue, though, I think, it's unrelated to our topic here: #373
@hernandp If you have some time, and willpower, would you have a look on this, if the "round-2" is OK in general according to you as well? Thanks a lot!
lgblgblgb
commented
1 year ago
PolyMega intro seems to produce(d) empty screen on Xemu. Initial guess was a DMA problem, but it turned out to be a glyph-trimming issue. It's a bit unclear for now, if it's not problematic on MEGA65 either (ie, compared to the document at least!).
Round-1
Author of PolyMega (Mirage_BD) looked into the issue, and suggested a solution as can be seen in commit f80a4f3bbc478920c03cbe233452a6ac8045c420 Discord discussion: https://discord.com/channels/719326990221574164/1043843197803175976/1113091458556252243
The change was relative simple:
change this:
const Uint8 glyph_trim = SXA_TRIM_RIGHT_BITS012(char_value) + (SXA_TRIM_RIGHT_BIT3(color_data) ? 8 : 0);to this:
const Uint8 glyph_trim = SXA_TRIM_RIGHT_BITS012(char_value);It seemed, that the bit3 stuff is mostly ignored by MEGA65 even if it's in contradict with the documentation. This change fixed PolyMega to also work on Xemu/MEGA65.
Round-2
It turned out that a fix above breaks trimming in NCM mode though. Discussion on Discord: https://discord.com/channels/719326990221574164/781481205639020554/1113877474292551690 commit is: 368a7c3c8fd6a702a0043edb886abfc37b69bd93
This change idea from Mirage_BD suggested this line instead:
const Uint8 glyph_trim = SXA_TRIM_RIGHT_BITS012(char_value) + ((SXA_TRIM_RIGHT_BIT3(color_data) & (SXA_4BIT_PER_PIXEL(color_data)>>1)) ? 8 : 0);Conclusion
This, it should be tested, if it's really OK in all cases for now. Also there are at least one trimming related other issue, though, I think, it's unrelated to our topic here: #373
@hernandp If you have some time, and willpower, would you have a look on this, if the "round-2" is OK in general according to you as well? Thanks a lot!