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| author | user <user@clank> | 2026-07-18 21:56:21 +0200 |
|---|---|---|
| committer | user <user@clank> | 2026-07-18 21:56:21 +0200 |
| commit | bea52bc8f99ee6dbcc8154a366560fc18e7b24c8 (patch) | |
| tree | 0772b5d9e98de7f6c495198844c230537c7fb9d6 /src/term.asm | |
| parent | term: SCY ring-scroll - scroll writes ONE map row; OSK toggle is 212 cycles (diff) | |
| download | gbos-bea52bc8f99ee6dbcc8154a366560fc18e7b24c8.tar.gz gbos-bea52bc8f99ee6dbcc8154a366560fc18e7b24c8.tar.xz gbos-bea52bc8f99ee6dbcc8154a366560fc18e7b24c8.zip | |
term: latch SCY in VBlank - fix ring-scroll shear on live displays
The ring-scroll wrote SCY mid-frame; SCY is sampled per scanline (on
hardware and in sl0pboy's PPU), so a scroll landing mid-frame rendered
the top of the frame at the old offset and the bottom at the new one -
a one-frame shear, invisible in frame-sampled GIF captures but ugly on
a live sixel view.
term_view_update now writes hSCY (HRAM) and a transparent VBlank ISR
(push af / apply / pop af / reti, same profile as TimerISR) copies it
to rSCY, so the view only ever moves at frame boundaries. The scroll's
tile+map writes stay immediate: the new map row is invisible at the
old SCY by construction (it's the ring row one past the visible 18).
Diffstat (limited to '')
| -rw-r--r-- | src/term.asm | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/src/term.asm b/src/term.asm index 6a94024..46cd23e 100644 --- a/src/term.asm +++ b/src/term.asm @@ -60,6 +60,7 @@ term_init:: ld [rLCDC], a ; LCD off ld [rSCX], a ld [rSCY], a + ldh [hSCY], a ; keep the VBlank latch in sync ; Load all 8 CGB BG palettes from PalData (see tools/gencolor.py). Palettes ; 0 and 2..7 are the 7 Fano-plane text palettes (each = bg + 3 of our 7 @@ -168,8 +169,8 @@ term_view_update:: add a add a add a ; *8 px - ld [rSCY], a - ret + ldh [hSCY], a ; latched: the VBlank ISR applies it, so the + ret ; view never moves mid-frame (no shear) ; ----------------------------------------------------------------------------- ; map_row_one - write the BG-map row for logical row A (0..17): tile indices |