diff options
| 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/hram.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/hram.asm | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/src/hram.asm b/src/hram.asm index 9e65982..facccd0 100644 --- a/src/hram.asm +++ b/src/hram.asm @@ -17,6 +17,10 @@ SECTION "hram_vars", HRAM hCurBankRAM: DS 1 ; shadow of active cart-RAM bank hCurBankWRAM: DS 1 ; shadow of active SVBK bank hSwitchTgt: DS 2 ; &incoming PCB (set before the pushes clobber DE) +hSCY:: DS 1 ; VBlank-latched SCY: term_view_update writes this, + ; the VBlank ISR applies it - a mid-frame SCY write + ; would shear the picture (SCY is sampled per + ; scanline), so ring-scrolls land at frame boundaries ; ----------------------------------------------------------------------------- ; Source image (lives in ROM0); CopyHramCode blits it to HRAM at boot. |