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10_custom_graphics.asm
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10_custom_graphics.asm
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include "gbhw.inc"
;-------------- INTERRUPT VECTORS ------------------------
; specific memory addresses are called when a hardware interrupt triggers
SECTION "Vblank", ROM0[$0040]
reti
SECTION "LCDC", ROM0[$0048]
reti
SECTION "Timer", ROM0[$0050]
reti
SECTION "Serial", ROM0[$0058]
reti
SECTION "Joypad", ROM0[$0060]
reti
;----------- END INTERRUPT VECTORS -------------------
SECTION "ROM_entry_point", ROM0[$0100] ; ROM is given control from boot here
nop
jp code_begins
;------------- BEGIN ROM HEADER ----------------
; The gameboy reads this info (before handing control over to ROM)
SECTION "rom header", ROM0[$0104]
NINTENDO_LOGO
ROM_HEADER " HELLO WORLD "
; by convention, *.asm files add code to the ROM when included. *.inc files
; do not add code. They only define constants or macros. The macros add code
; to the ROM when called
include "ibmpc1.inc" ; used to generate ascii characters in our ROM
include "memory.asm" ; used to copy Monochrome ascii characters to VRAM
code_begins:
di ; disable interrupts
ld SP, $FFFF ; set stack to top of HRAM
call lcd_Stop
; load ascii tiles (inserted below with chr_IBMPC1 macro) into VRAM
ld hl, ascii_tiles ; ROM address where we insert ascii tiles
ld de, _VRAM ; destination. Going to copy ascii to video ram
; bc = byte-count. Aka how many bytes to copy
ld bc, ascii_tiles_end - ascii_tiles
call mem_CopyVRAM
ld a, [rLCDC]
or LCDCF_ON
ld [rLCDC], a ; turn LCD back on
; need to set palette from [black & white] to [four shades of grey]
ld a, %11100100 ; load pallette colors (to 4 shades)
; each shade is 2 bits. So we set darkest to lightest using 11100100
; 11 (black) 10 (dark) 01 (light) 00 (white)
ld [rBGP], a ; set background pallet
ld [rOBP0], a ; set sprite/obj pallete 0
ld [rOBP1], a ; set sprite/ obj pallete 1
.loop
halt
nop
jp .loop
; You can turn off LCD at any time, but it's bad for LCD if NOT done at vblank
lcd_Stop:
ld a, [rLCDC] ; LCD-Config
and LCDCF_ON ; compare config to lcd-on flag
ret z ; return if LCD is already off
.wait4vblank
ldh a, [rLY] ; ldh is a faster version of ld if in [$FFxx] range
cp 145 ; are we at line 145 yet? (finished drawing screen then)
jr nz, .wait4vblank
.stopLCD
ld a, [rLCDC]
xor LCDCF_ON ; XOR lcd-on bit with lcd control bits. (toggles LCD off)
ld [rLCDC], a ; `a` holds result of XOR operation
ret
; it's necessary to use a macro to generate characters. That way we can use
; custom characters to represent the 4 shades of grey
; (otherwise we'd have to use 0,1,2,3)
chr_custom: MACRO
PUSHO ; push compiler options so that I can change the meaning of
; 0,1,2,3 graphics to something better. Like .-*@
; change graphics characters. Start the line with ` (for graphics)
; . = 00
; - = 01
; * = 10
; @ = 11
OPT g.~*@
DW `...~~**@
DW `..~~**@@
DW `.~~**@@*
DW `~~**@@**
DW `~**@@**~
DW `**@@**~~
DW `*@@**~~.
DW `@@**~~..
POPO ; restore compiler options
DW `00011223 ; an example of using standard graphics
ENDM
ascii_tiles:
chr_custom
ascii_tiles_end:
; ================ QUESTIONS FOR STUDENT ===========================
; Can you blank the entire screen?