ref: 395ebd83866161a93276f030bbf67f6ac0895f0f
dir: /home/video.asm/
; Functions dealing with VRAM. DMATransfer:: ; Return carry if the transfer is completed. ldh a, [hDMATransfer] and a ret z ; Start transfer ldh [rHDMA5], a ; Execution is halted until the transfer is complete. xor a ldh [hDMATransfer], a scf ret UpdateBGMapBuffer:: ; Copy [hBGMapTileCount] 16x8 tiles from wBGMapBuffer ; to bg map addresses in wBGMapBufferPtrs. ; [hBGMapTileCount] must be even since this is done in pairs. ; Return carry on success. ldh a, [hBGMapUpdate] and a ret z ldh a, [rVBK] push af ld [hSPBuffer], sp ld hl, wBGMapBufferPtrs ld sp, hl ; We can now pop the addresses of affected spots on the BG Map ld hl, wBGMapPalBuffer ld de, wBGMapBuffer .next ; Copy a pair of 16x8 blocks (one 16x16 block) rept 2 ; Get our BG Map address pop bc ; Palettes ld a, 1 ldh [rVBK], a ld a, [hli] ld [bc], a inc c ld a, [hli] ld [bc], a dec c ; Tiles ld a, 0 ldh [rVBK], a ld a, [de] inc de ld [bc], a inc c ld a, [de] inc de ld [bc], a endr ; We've done 2 16x8 blocks ldh a, [hBGMapTileCount] dec a dec a ldh [hBGMapTileCount], a jr nz, .next ldh a, [hSPBuffer] ld l, a ldh a, [hSPBuffer + 1] ld h, a ld sp, hl pop af ldh [rVBK], a xor a ldh [hBGMapUpdate], a scf ret WaitTop:: ; Wait until the top third of the BG Map is being updated. ldh a, [hBGMapMode] and a ret z ldh a, [hBGMapThird] and a jr z, .done call DelayFrame jr WaitTop .done xor a ldh [hBGMapMode], a ret UpdateBGMap:: ; Update the BG Map, in thirds, from wTilemap and wAttrmap. ldh a, [hBGMapMode] and a ret z ; BG Map 0 dec a ; 1 jr z, .Tiles dec a ; 2 jr z, .Attr ; BG Map 1 dec a ldh a, [hBGMapAddress] ld l, a ldh a, [hBGMapAddress + 1] ld h, a push hl xor a ; LOW(vBGMap1) ldh [hBGMapAddress], a ld a, HIGH(vBGMap1) ldh [hBGMapAddress + 1], a ldh a, [hBGMapMode] push af cp 3 call z, .Tiles pop af cp 4 call z, .Attr pop hl ld a, l ldh [hBGMapAddress], a ld a, h ldh [hBGMapAddress + 1], a ret .Attr: ld a, 1 ldh [rVBK], a hlcoord 0, 0, wAttrmap call .update ld a, 0 ldh [rVBK], a ret .Tiles: hlcoord 0, 0 .update ld [hSPBuffer], sp ; Which third? ldh a, [hBGMapThird] and a ; 0 jr z, .top dec a ; 1 jr z, .middle ; 2 THIRD_HEIGHT EQU SCREEN_HEIGHT / 3 .bottom ld de, 2 * THIRD_HEIGHT * SCREEN_WIDTH add hl, de ld sp, hl ldh a, [hBGMapAddress + 1] ld h, a ldh a, [hBGMapAddress] ld l, a ld de, 2 * THIRD_HEIGHT * BG_MAP_WIDTH add hl, de ; Next time: top third xor a jr .start .middle ld de, THIRD_HEIGHT * SCREEN_WIDTH add hl, de ld sp, hl ldh a, [hBGMapAddress + 1] ld h, a ldh a, [hBGMapAddress] ld l, a ld de, THIRD_HEIGHT * BG_MAP_WIDTH add hl, de ; Next time: bottom third ld a, 2 jr .start .top ld sp, hl ldh a, [hBGMapAddress + 1] ld h, a ldh a, [hBGMapAddress] ld l, a ; Next time: middle third ld a, 1 .start ; Which third to update next time ldh [hBGMapThird], a ; Rows of tiles in a third ld a, SCREEN_HEIGHT / 3 ; Discrepancy between wTilemap and BGMap ld bc, BG_MAP_WIDTH - (SCREEN_WIDTH - 1) .row ; Copy a row of 20 tiles rept SCREEN_WIDTH / 2 - 1 pop de ld [hl], e inc l ld [hl], d inc l endr pop de ld [hl], e inc l ld [hl], d add hl, bc dec a jr nz, .row ldh a, [hSPBuffer] ld l, a ldh a, [hSPBuffer + 1] ld h, a ld sp, hl ret Serve1bppRequest:: ; Only call during the first fifth of VBlank ld a, [wRequested1bpp] and a ret z ; Back out if we're too far into VBlank ldh a, [rLY] cp LY_VBLANK ret c cp LY_VBLANK + 2 ret nc ; Copy [wRequested1bpp] 1bpp tiles from [wRequested1bppSource] to [wRequested1bppDest] ld [hSPBuffer], sp ; Source ld hl, wRequested1bppSource ld a, [hli] ld h, [hl] ld l, a ld sp, hl ; Destination ld hl, wRequested1bppDest ld a, [hli] ld h, [hl] ld l, a ; # tiles to copy ld a, [wRequested1bpp] ld b, a xor a ld [wRequested1bpp], a .next rept 3 pop de ld [hl], e inc l ld [hl], e inc l ld [hl], d inc l ld [hl], d inc l endr pop de ld [hl], e inc l ld [hl], e inc l ld [hl], d inc l ld [hl], d inc hl dec b jr nz, .next ld a, l ld [wRequested1bppDest], a ld a, h ld [wRequested1bppDest + 1], a ld [wRequested1bppSource], sp ldh a, [hSPBuffer] ld l, a ldh a, [hSPBuffer + 1] ld h, a ld sp, hl ret Serve2bppRequest:: ; Only call during the first fifth of VBlank ld a, [wRequested2bpp] and a ret z ; Back out if we're too far into VBlank ldh a, [rLY] cp LY_VBLANK ret c cp LY_VBLANK + 2 ret nc jr _Serve2bppRequest Serve2bppRequest_VBlank:: ld a, [wRequested2bpp] and a ret z _Serve2bppRequest:: ; Copy [wRequested2bpp] 2bpp tiles from [wRequested2bppSource] to [wRequested2bppDest] ld [hSPBuffer], sp ; Source ld hl, wRequested2bppSource ld a, [hli] ld h, [hl] ld l, a ld sp, hl ; Destination ld hl, wRequested2bppDest ld a, [hli] ld h, [hl] ld l, a ; # tiles to copy ld a, [wRequested2bpp] ld b, a xor a ld [wRequested2bpp], a .next rept 7 pop de ld [hl], e inc l ld [hl], d inc l endr pop de ld [hl], e inc l ld [hl], d inc hl dec b jr nz, .next ld a, l ld [wRequested2bppDest], a ld a, h ld [wRequested2bppDest + 1], a ld [wRequested2bppSource], sp ldh a, [hSPBuffer] ld l, a ldh a, [hSPBuffer + 1] ld h, a ld sp, hl ret AnimateTileset:: ; Only call during the first fifth of VBlank ldh a, [hMapAnims] and a ret z ; Back out if we're too far into VBlank ldh a, [rLY] cp LY_VBLANK ret c cp LY_VBLANK + 7 ret nc ldh a, [hROMBank] push af ld a, BANK(_AnimateTileset) rst Bankswitch ldh a, [rSVBK] push af ld a, BANK(wTilesetAnim) ldh [rSVBK], a ldh a, [rVBK] push af ld a, 0 ldh [rVBK], a call _AnimateTileset pop af ldh [rVBK], a pop af ldh [rSVBK], a pop af rst Bankswitch ret