fox32rom/background.asm

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; background routines
const background: 0x02000000 ; pointer to background framebuffer
; fill the whole background with a color
; inputs:
; r0: color
; outputs:
; none
fill_background:
push r1
push r31
mov r1, background
mov r31, 0x0004B000 ; 640*480
fill_background_loop:
mov [r1], r0
add r1, 4
loop fill_background_loop
pop r31
pop r1
ret
; draw a filled rectangle to the background
; inputs:
; r0: X coordinate of top-left
; r1: Y coordinate of top-left
; r2: X size
; r3: Y size
; r4: color
; outputs:
; none
draw_filled_rectangle_to_background:
push r0
push r1
push r2
push r3
push r4
push r5
push r6
; calculate pointer to the framebuffer
mul r1, 2560 ; y * 2560 (640 * 4 = 2560)
mul r0, 4 ; x * 4
add r0, r1 ; y * 2560 + (x * 4)
add r0, background ; r0: pointer to framebuffer
mov r6, r2
mul r6, 4 ; multiply the X size by 4, since 4 bytes per pixel
draw_filled_rectangle_to_background_y_loop:
mov r5, r2 ; x counter
draw_filled_rectangle_to_background_x_loop:
mov [r0], r4
add r0, 4 ; increment framebuffer pointer
dec r5
ifnz jmp draw_filled_rectangle_to_background_x_loop ; loop if there are still more X pixels to draw
sub r0, r6 ; return to the beginning of this line
add r0, 2560 ; 640*4, increment to the next line
dec r3
ifnz jmp draw_filled_rectangle_to_background_y_loop ; loop if there are still more Y pixels to draw
pop r6
pop r5
pop r4
pop r3
pop r2
pop r1
pop r0
ret
; draw a single font tile to the background
; inputs:
; r0: tile number
; r1: X coordinate
; r2: Y coordinate
; r3: foreground color
; r4: background color
; outputs:
; none
draw_font_tile_to_background:
push r0
push r1
push r2
push r5
push r6
;movz.8 r0, r0 ; ensure the tile number is a single byte
; calculate pointer to the tile data
push r1
push r2
mov r1, 8 ; tile width
mov r2, 16 ; tile height
mul r1, r2
mul r0, r1
mul r0, 4 ; 4 bytes per pixel
add r0, font ; r0: pointer to tile data
pop r2
pop r1
; calculate pointer to the framebuffer
mul r2, 2560 ; y * 2560 (640 * 4 = 2560)
mul r1, 4 ; x * 4
add r1, r2 ; y * 2560 + (x * 4)
add r1, background ; r1: pointer to framebuffer
mov r6, 16 ; y counter
draw_font_tile_to_background_y_loop:
mov r5, 8 ; x counter
draw_font_tile_to_background_x_loop:
mov r2, [r0]
cmp r2, 0xFF000000
ifz jmp draw_font_tile_to_background_x_loop_background
; drawing foreground pixel
cmp r3, 0x00000000 ; is the foreground color supposed to be transparent?
ifz jmp draw_font_tile_to_background_x_loop_end
mov [r1], r3 ; draw foreground color
jmp draw_font_tile_to_background_x_loop_end
draw_font_tile_to_background_x_loop_background:
; drawing background pixel
cmp r4, 0x00000000 ; is the background color supposed to be transparent?
ifz jmp draw_font_tile_to_background_x_loop_end
mov [r1], r4 ; draw background color
draw_font_tile_to_background_x_loop_end:
add r0, 4 ; increment tile pointer
add r1, 4 ; increment framebuffer pointer
dec r5
ifnz jmp draw_font_tile_to_background_x_loop ; loop if there are still more X pixels to draw
sub r1, 32 ; 8*4, return to the beginning of this line
add r1, 2560 ; 640*4, increment to the next line
dec r6
ifnz jmp draw_font_tile_to_background_y_loop ; loop if there are still more Y pixels to draw
pop r6
pop r5
pop r2
pop r1
pop r0
ret
; draw text on the background
; inputs:
; r0: pointer to null-terminated string
; r1: X coordinate
; r2: Y coordinate
; r3: foreground color
; r4: background color
; outputs:
; r1: X coordinate of end of text
draw_str_to_background:
push r0
push r5
mov r5, r0
draw_str_to_background_loop:
movz.8 r0, [r5]
call draw_font_tile_to_background
inc r5
add r1, 8
cmp.8 [r5], 0x00
ifnz jmp draw_str_to_background_loop
pop r5
pop r0
ret