split into several files

Code/render.asm

@@ -0,0 +1,155 @@
+INCLUDE "hardware.inc"
+
+RENDER_IN_HBL EQU 0
+
+EXPORT Video, Rendered
+SECTION "Render Memory", HRAM
+LinesLeft: ds 1     ; number of lines left to render
+TilesLeft: ds 1     ; number of tiles left to render in current line
+Video: ds 2         ; progressing pointer in tilemap (VRAM)
+Rendered: ds 2      ; progressing pointer in old buffer
+
+SECTION "V-Blank Interrupt Handler", ROM0[$40]
+VBlankInterruptHandler:
+	jr LCDStatInterruptHandler
+
+SECTION "LCD Stat Interrupt Handler", ROM0[$48]
+LCDStatInterruptHandler:
+	; save registers
+	push af
+	push bc
+    
+	; check there are tiles to render
+	ldh a, [LinesLeft]
+	or a
+	jr z, .exit
+	
+	; move lines left to B
+	ld b, a
+
+	push de
+	push hl
+
+.render	
+	; load buffer pointer into DE
+	ld hl, Video
+	ld a, [hl+]
+	ld d, [hl]
+	ld e, a	
+
+	; load video pointer into HL
+	ld hl, Rendered
+	ld a, [hl+]
+	ld h, [hl]
+	ld l, a
+	
+	; load counters
+	ldh a, [TilesLeft]
+	ld c, a
+
+.loop
+	; check we can still render
+	ldh a, [rSTAT]
+	and a, STATF_BUSY
+	jr nz, .finish
+
+	; copy one byte
+	ld a, [hl+]
+	ld [de], a
+	inc e ; it will never overflow since it only increments
+	      ; up to 20 bytes starting on 32 byte boundaries
+
+	; loop while there are tiles to render
+	dec c
+	jr nz, .loop
+
+	; go to next line
+	ld a, e
+	add a, 32 - 20
+	ld e, a
+	jr nc, .nocarry
+	inc d
+.nocarry
+	
+	; loop while there are lines to render
+	dec b
+	jr z, .finish
+	
+	; reset tile counter
+	ld c, 20 
+
+	jr .loop
+
+.finish
+	; save counters
+	ld a, c
+	ldh [TilesLeft], a
+	ld a, b
+	ldh [LinesLeft], a
+	
+	; save incremented video pointer and buffer pointer 
+	ld a, e
+	ldh [Video], a
+	ld a, d
+	ldh [Video + 1], a
+
+	ld a, l
+	ldh [Rendered], a
+	ld a, h
+	ldh [Rendered + 1], a
+
+	; restore registers saved in interrupt handler
+	pop hl
+	pop de
+
+.exit
+	pop bc
+	pop af
+
+	; return from v-blank or lcd interrupt
+	reti
+
+EXPORT StartRender	
+SECTION "StartRender", ROM0
+StartRender:
+	; start rendering
+	ld a, 20
+	ldh [TilesLeft], a
+	ld a, 18
+	ldh [LinesLeft], a
+	
+	; enable v-blank and lcd stat interrupt for h-blank
+	; rendering routine is too slow for lcdc right now so disabled
+IF RENDER_IN_HBL != 0
+	ld a, IEF_VBLANK | IEF_LCDC
+ELSE
+	ld a, IEF_VBLANK
+ENDC
+	ld [rIE], a
+	xor a
+	ei
+	ldh [rIF], a
+	
+	ret
+
+EXPORT WaitRender	
+SECTION "WaitRender", ROM0
+WaitRender:
+	ldh a, [LinesLeft]
+	ld b, a
+	ldh a, [TilesLeft]
+	or a, b
+	ret z
+	halt
+	jr WaitRender
+
+IF RENDER_IN_HBL != 0
+	; enable only v-blank interrupt and wait for vbl
+	ld a, IEF_VBLANK
+	ld [rIE], a
+	xor a
+	ldh [rIF], a
+	halt
+ENDC
+
+	ret