Entry 339

Adjust Screen moves the picture: SetDisplayOffset's units, and the presenter's shift

2026-10-01renderuiengine

Filescrates/piney-gs/src/lib.rscrates/piney-game/src/main.rscrates/piney-game/src/mode.rscrates/piney-game/src/session.rscrates/piney-game/src/desktop.rscrates/piney-game/src/world.rscrates/piney-game/src/area.rsdocs/engine/overview.md

Adjust Screen (the desktop's ScreenMenu, INF SLUS_202.67:0x0016d4d0, and the field Option's, INF GCMN.PRG:0x0053f060) calls ccSystem::SetDisplayOffset(x, y) every frame it is open. The port's menus already asked for it (Request::DisplayOffset), but the game dropped the request, so the option did nothing (50, 51, 196). The picture now moves.

What the offset is in

SetDisplayOffset (INF SLUS_202.67:0x0010ab30) keeps (x, y) at +0x20 / +0x22 and writes base + x (clamped 0..4095) and base + y (0..2046) into the DX and DY of both display buffers' DISPLAY register (+0xbf8, +0xc20). With the field flag (+0xbd6) 0 it also writes them, y + 1, into read circuit 1's pair at +0xe10 / +0xe20, the game's deflicker (340). The base (+0x1c, +0x1e) is DISPLAY's DX and DY as SetScreenModeMain (0x0010ad40) leaves them after sceGsSetDefDBuff (0x0010b57c-0x0010b594).

ccSystem::Init (0x0010a900) asks SetScreenMode(512, 448, 0), which SetScreenModeMain turns into sceGsResetGraph(0, 1, 2, 0): NTSC, interlaced, frame mode, one 448-line buffer. sceGsSetDefDispEnv (0x0010de50) sets, for NTSC interlaced:

MAGH = (2559 + w) / w - 1      4 at 512 wide (5 clocks a pixel), 3 at 640
DX   = 636 + dx * (MAGH + 1)
DY   = 50 + dy
DH   = 2 h - 1 (field mode), h - 1 (frame mode)

So DX counts video clocks (2,560 across the picture at either width), and DY counts lines of the interlaced frame: one row of the 448. Adjust Screen steps x by 3 (-48..48) and y by 1 (-16..16), up to 9.6 pixels across and 16 rows down. An earlier draft of this change took y as half-lines and halved it; DH = h - 1 for the 448-line frame mode shows a DY unit is a whole row.

MUT, OUT and QUA have the same SetDisplayOffset (MUT 0x0010abd0, OUT 0x0010b1a0, QUA 0x0010af70; OUT's and QUA's differ from INF's only in instruction scheduling) and the same constants in sceGsSetDefDispEnv (636, 50, 72, 656).

The port

Event::DisplayOffset { x, y } carries the request out of the desktop, the title and top page (through desktop::event), the town (world.rs) and the fields (area.rs). Two places set it from the save, as the game does through its own SetDisplayOffset(screenX, screenY) (title): the title's boot, where the kept settings (crates/piney-game/src/settings.rs, screen_x / screen_y) are already in the save, and LoadGame.

The app keeps the last offset and hands Presenter::present a shift of (x / 5, y) in pixels of the 512 x 448 picture. The presenter moves the picture in its shader (picture(): the sample point less the shift, black outside the picture), inside the same 4:3 box. A viewport moved by the shift was tried first, but wgpu rejects a viewport that leaves the attachment, which a window with no bars would do at any offset. The console overlay does not move.

present_moves_the_picture_by_the_display_offset presents a cleared frame moved an eighth across and down on a 600 x 450 surface: black left of x 75 and above y 56, the colour from there. options_kept_across_the_parts writes screen_x = -12, screen_y = 7 into the settings file and sees DisplayOffset { x: -12, y: 7 } at power-on.