diff options
| -rw-r--r-- | main.asm | 362 |
1 files changed, 163 insertions, 199 deletions
@@ -141,153 +141,120 @@ INCLUDE "engine/text.asm" DMATransfer: ; 15d8 -; DMA transfer -; return carry if successful +; Return carry if the transfer is completed. -; anything to transfer? ld a, [hDMATransfer] and a ret z -; start transfer + +; Start transfer ld [rHDMA5], a -; indicate that transfer has occurred + +; Execution is halted until the transfer is complete. + xor a ld [hDMATransfer], a -; successful transfer scf ret ; 15e3 UpdateBGMapBuffer: ; 15e3 -; write [$ffdc] 16x8 tiles from BGMapBuffer to bg map addresses in BGMapBufferPtrs -; [$ffdc] must be even since this is done in 16x16 blocks +; Copy [$ffdc] 16x8 tiles from BGMapBuffer +; to bg map addresses in BGMapBufferPtrs. + +; [$ffdc] must be even since this is done in pairs. -; return carry if successful +; Return carry on success. -; any tiles to update? ld a, [hBGMapUpdate] and a ret z -; save wram bank + ld a, [rVBK] push af -; save sp ld [hSPBuffer], sp - -; temp stack + ld hl, BGMapBufferPtrs ld sp, hl -; we can now pop the addresses of affected spots in bg map - -; get pal and tile buffers + +; We can now pop the addresses of affected spots on the BG Map + ld hl, BGMapPalBuffer ld de, BGMapBuffer -.loop -; draw one 16x16 block -; top half: +.next +; Copy a pair of 16x8 blocks (one 16x16 block) -; get bg map address +rept 2 +; Get our BG Map address pop bc -; update palettes - ld a, $1 - ld [rVBK], a -; tile 1 - ld a, [hli] - ld [bc], a - inc c -; tile 2 - ld a, [hli] - ld [bc], a - dec c -; update tiles - ld a, $0 - ld [rVBK], a -; tile 1 - ld a, [de] - inc de - ld [bc], a - inc c -; tile 2 - ld a, [de] - inc de - ld [bc], a - -; bottom half: -; get bg map address - pop bc -; update palettes - ld a, $1 +; Palettes + ld a, 1 ld [rVBK], a -; tile 1 + ld a, [hli] ld [bc], a inc c -; tile 2 ld a, [hli] ld [bc], a dec c -; update tiles - ld a, $0 + +; Tiles + ld a, 0 ld [rVBK], a -; tile 1 + ld a, [de] inc de ld [bc], a inc c -; tile 2 ld a, [de] inc de ld [bc], a - -; we've done 2 16x8 blocks +endr + +; We've done 2 16x8 blocks ld a, [$ffdc] dec a dec a ld [$ffdc], a - -; if there are more left, get the next 16x16 block - jr nz, .loop - - -; restore sp + + jr nz, .next + + ld a, [hSPBuffer] ld l, a - ld a, [$ffda] + ld a, [hSPBuffer + 1] ld h, a ld sp, hl - -; restore vram bank + pop af ld [rVBK], a - -; we don't need to update bg map until new tiles are loaded + xor a ld [hBGMapUpdate], a - -; successfully updated bg map scf ret ; 163a WaitTop: ; 163a +; Wait until the top third of the BG Map is being updated. + ld a, [hBGMapMode] and a ret z - -; wait until top third of bg map can be updated + ld a, [hBGMapThird] and a - jr z, .quit - + jr z, .done + call DelayFrame jr WaitTop - -.quit + +.done xor a ld [hBGMapMode], a ret @@ -295,133 +262,141 @@ WaitTop: ; 163a UpdateBGMap: ; 164c -; get mode +; Update the BG Map, in thirds, from TileMap and AttrMap. + ld a, [hBGMapMode] and a ret z - -; don't save bg map address + +; BG Map 0 dec a ; 1 - jr z, .tiles + jr z, .Tiles dec a ; 2 - jr z, .attr - dec a ; ? - -; save bg map address + jr z, .Attr + +; BG Map 1 + dec a + ld a, [hBGMapAddress] ld l, a - ld a, [$ffd7] + ld a, [hBGMapAddress + 1] ld h, a push hl -; bg map 1 (VBGMap1) xor a ld [hBGMapAddress], a - ld a, $9c - ld [$ffd7], a - -; get mode again + ld a, VBGMap1 >> 8 + ld [hBGMapAddress + 1], a + ld a, [hBGMapMode] push af cp 3 - call z, .tiles + call z, .Tiles pop af cp 4 - call z, .attr - -; restore bg map address + call z, .Attr + pop hl ld a, l ld [hBGMapAddress], a ld a, h - ld [$ffd7], a + ld [hBGMapAddress + 1], a ret - -.attr -; switch vram banks + + +.Attr ld a, 1 ld [rVBK], a -; bg map 1 + ld hl, AttrMap - call .getthird -; restore vram bank + call .update + ld a, 0 ld [rVBK], a ret - -.tiles -; bg map 0 + + +.Tiles ld hl, TileMap - -.getthird -; save sp + + +.update ld [hSPBuffer], sp -; # tiles to move down * 6 (which third?) +; Which third? ld a, [hBGMapThird] and a ; 0 jr z, .top dec a ; 1 jr z, .middle + ; 2 -; .bottom ; 2 -; move 12 tiles down - ld de, $00f0 ; TileMap(0,12) - TileMap + +THIRD_HEIGHT EQU SCREEN_HEIGHT / 3 + + +.bottom + ld de, 2 * THIRD_HEIGHT * SCREEN_WIDTH add hl, de -; stack now points to source ld sp, hl -; get bg map address - ld a, [$ffd7] + + ld a, [hBGMapAddress + 1] ld h, a ld a, [hBGMapAddress] ld l, a -; move 12 tiles down - ld de, $0180 ; bgm(0,12) + + ld de, 2 * THIRD_HEIGHT * BG_MAP_WIDTH add hl, de -; start at top next time + +; Next time: top third xor a jr .start - + + .middle -; move 6 tiles down - ld de, $0078 ; TileMap(0,6) - TileMap + ld de, THIRD_HEIGHT * SCREEN_WIDTH add hl, de -; stack now points to source ld sp, hl -; get bg map address - ld a, [$ffd7] + + ld a, [hBGMapAddress + 1] ld h, a ld a, [hBGMapAddress] ld l, a -; move 6 tiles down - ld de, $00c0 ; bgm(0,6) + + ld de, THIRD_HEIGHT * BG_MAP_WIDTH add hl, de -; start at bottom next time + +; Next time: bottom third ld a, 2 jr .start - + + .top -; stack now points to source ld sp, hl -; get bg map address - ld a, [$ffd7] + + ld a, [hBGMapAddress + 1] ld h, a ld a, [hBGMapAddress] ld l, a -; start at middle next time + +; Next time: middle third ld a, 1 - + + .start -; which third to draw next update +; Which third to update next time ld [hBGMapThird], a -; # rows per third - ld a, 6 ; SCREEN_HEIGHT / 3 -; # tiles from the edge of the screen to the next row - ld bc, $000d ; BG_WIDTH + 1 - SCREEN_WIDTH - + +; Rows of tiles in a third + ld a, SCREEN_HEIGHT / 3 + +; Discrepancy between TileMap and BGMap + ld bc, BG_MAP_WIDTH - (SCREEN_WIDTH - 1) + + .row -; write a row of 20 tiles -rept 9 +; Copy a row of 20 tiles +rept SCREEN_WIDTH / 2 - 1 pop de ld [hl], e inc l @@ -432,16 +407,15 @@ endr ld [hl], e inc l ld [hl], d -; next row + add hl, bc -; done? dec a jr nz, .row - -; restore sp + + ld a, [hSPBuffer] ld l, a - ld a, [$ffda] + ld a, [hSPBuffer + 1] ld h, a ld sp, hl ret @@ -449,47 +423,45 @@ endr SafeLoadTiles2: ; 170a -; only execute during first fifth of vblank -; any tiles to draw? +; Only call during the first fifth of VBlank + ld a, [$cf6c] and a ret z -; abort if too far into vblank + +; Back out if we're too far into VBlank ld a, [rLY] -; ly = 144-145? cp 144 ret c cp 146 ret nc - + GetTiles2: ; 1717 -; load [$cf6c] tiles from [$cf6d-e] to [$cf6f-70] -; save sp +; Copy [$cf6c] 1bpp tiles from [$cf6d-e] to [$cf6f-70] + ld [hSPBuffer], sp - -; sp = [$cf6d-e] tile source + +; Source ld hl, $cf6d ld a, [hli] ld h, [hl] ld l, a ld sp, hl -; hl = [$cf6f-70] tile dest +; Destination ld hl, $cf6f ld a, [hli] ld h, [hl] ld l, a -; # tiles to draw +; # tiles to copy ld a, [$cf6c] ld b, a - -; clear tile queue + xor a ld [$cf6c], a - -.loop -; put 1 tile (16 bytes) into hl from sp + +.next rept 3 pop de @@ -510,25 +482,22 @@ endr ld [hl], d inc l ld [hl], d -; next tile + inc hl -; done? dec b - jr nz, .loop - -; update $cf6f-70 + jr nz, .next + + ld a, l ld [$cf6f], a ld a, h ld [$cf70], a - -; update $cf6d-e + ld [$cf6d], sp - -; restore sp + ld a, [hSPBuffer] ld l, a - ld a, [$ffda] + ld a, [hSPBuffer + 1] ld h, a ld sp, hl ret @@ -536,56 +505,54 @@ endr SafeLoadTiles: ; 1769 -; only execute during first fifth of vblank -; any tiles to draw? +; Only call during the first fifth of VBlank + ld a, [$cf67] and a ret z -; abort if too far into vblank + +; Back out if we're too far into VBlank ld a, [rLY] -; ly = 144-145? cp 144 ret c cp 146 ret nc jr GetTiles - + + LoadTiles: ; 1778 -; use only if time is allotted -; any tiles to draw? + ld a, [$cf67] and a ret z -; get tiles - + GetTiles: ; 177d -; load [$cf67] tiles from [$cf68-9] to [$cf6a-b] +; Copy [$cf67] 2bpp tiles from [$cf68-9] to [$cf6a-b] -; save sp ld [hSPBuffer], sp -; sp = [$cf68-9] tile source +; Source ld hl, $cf68 ld a, [hli] ld h, [hl] ld l, a ld sp, hl -; hl = [$cf6a-b] tile dest +; Destination ld hl, $cf6a ld a, [hli] ld h, [hl] ld l, a -; # tiles to draw +; # tiles to copy ld a, [$cf67] ld b, a -; clear tile queue + xor a ld [$cf67], a -.loop -; put 1 tile (16 bytes) into hl from sp +.next + rept 7 pop de ld [hl], e @@ -597,25 +564,22 @@ endr ld [hl], e inc l ld [hl], d -; next tile + inc hl -; done? dec b - jr nz, .loop - -; update $cf6a-b + jr nz, .next + + ld a, l ld [$cf6a], a ld a, h ld [$cf6b], a - -; update $cf68-9 + ld [$cf68], sp - -; restore sp + ld a, [hSPBuffer] ld l, a - ld a, [$ffda] + ld a, [hSPBuffer + 1] ld h, a ld sp, hl ret |