fox32rom/draw_text.asm
ry755 5f5771e823 fox32rom: Move text drawing to a generic routine
Instead of having lots of duplicate code for drawing text to overlays
and the background, move all of the actual drawing logic to a generic
routine that can be used to draw text to *any* type of framebuffer.
2022-02-12 20:42:37 -08:00

112 lines
3.0 KiB
NASM

; generic text drawing routines
; draw a single font tile to a framebuffer
; inputs:
; r0: tile number
; r1: X coordinate
; r2: Y coordinate
; r3: foreground color
; r4: background color
; r5: pointer to font graphics
; r6: font width
; r7: font height
; r8: pointer to framebuffer
; r9: framebuffer width (pixels)
; outputs:
; none
draw_font_tile_generic:
push r0
push r1
push r2
push r5
push r6
push r7
push r8
push r9
;movz.8 r0, r0 ; ensure the tile number is a single byte
; calculate pointer to the tile data
push r6
mul r6, r7
mul r0, r6
mul r0, 4 ; 4 bytes per pixel
add r0, r5 ; r0: pointer to tile data
pop r6
; calculate pointer to the framebuffer
mul r9, 4 ; 4 bytes per pixel
mul r2, r9 ; y * width * 4
mul r1, 4 ; x * 4
add r1, r2 ; y * width * 4 + (x * 4)
add r1, r8 ; r1: pointer to framebuffer
; r8: font width in bytes
mov r8, r6
mul r8, 4
draw_font_tile_generic_y_loop:
mov r5, r6 ; x counter
draw_font_tile_generic_x_loop:
mov r2, [r0]
cmp r2, 0xFF000000
ifz jmp draw_font_tile_generic_x_loop_background
; drawing foreground pixel
cmp r3, 0x00000000 ; is the foreground color supposed to be transparent?
ifz jmp draw_font_tile_generic_x_loop_end
mov [r1], r3 ; draw foreground color
jmp draw_font_tile_generic_x_loop_end
draw_font_tile_generic_x_loop_background:
; drawing background pixel
cmp r4, 0x00000000 ; is the background color supposed to be transparent?
ifz jmp draw_font_tile_generic_x_loop_end
mov [r1], r4 ; draw background color
draw_font_tile_generic_x_loop_end:
add r0, 4 ; increment tile pointer
add r1, 4 ; increment framebuffer pointer
dec r5
ifnz jmp draw_font_tile_generic_x_loop ; loop if there are still more X pixels to draw
sub r1, r8 ; return to the beginning of this line
add r1, r9 ; increment to the next line by adding the framebuffer width in bytes
dec r7 ; decrement height counter
ifnz jmp draw_font_tile_generic_y_loop ; loop if there are still more Y pixels to draw
pop r9
pop r8
pop r7
pop r6
pop r5
pop r2
pop r1
pop r0
ret
; draw text to a framebuffer
; inputs:
; r0: pointer to null-terminated string
; r1: X coordinate
; r2: Y coordinate
; r3: foreground color
; r4: background color
; r5: pointer to font graphics
; r6: font width
; r7: font height
; r8: pointer to framebuffer
; r9: framebuffer width
; outputs:
; r1: X coordinate of end of text
draw_str_generic:
push r0
push r10
mov r10, r0
draw_str_generic_loop:
movz.8 r0, [r10]
call draw_font_tile_generic
inc r10
add r1, r6
cmp.8 [r10], 0x00
ifnz jmp draw_str_generic_loop
pop r10
pop r0
ret