fox32rom/draw_rectangle.asm

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; generic rectangle drawing routines
; draw a filled rectangle to a framebuffer
; inputs:
; r0: X coordinate of top-left
; r1: Y coordinate of top-left
; r2: X size
; r3: Y size
; r4: color
; r5: pointer to framebuffer
; r6: framebuffer width (pixels)
; outputs:
; none
draw_filled_rectangle_generic:
push r0
push r1
push r2
push r3
push r4
push r5
push r6
push r7
; calculate pointer to the framebuffer
mul r6, 4 ; 4 bytes per pixel
mul r1, r6 ; y * width * 4
mul r0, 4 ; x * 4
add r0, r1 ; y * width * 4 + (x * 4)
add r5, r0
mov r0, r5 ; r0: pointer to framebuffer
mov r7, r6
mov r6, r2
mul r6, 4 ; multiply the X size by 4, since 4 bytes per pixel
draw_filled_rectangle_generic_y_loop:
mov r5, r2 ; x counter
draw_filled_rectangle_generic_x_loop:
mov [r0], r4
add r0, 4 ; increment framebuffer pointer
dec r5
ifnz jmp draw_filled_rectangle_generic_x_loop ; loop if there are still more X pixels to draw
sub r0, r6 ; return to the beginning of this line
add r0, r7 ; increment to the next line
dec r3
ifnz jmp draw_filled_rectangle_generic_y_loop ; loop if there are still more Y pixels to draw
pop r7
pop r6
pop r5
pop r4
pop r3
pop r2
pop r1
pop r0
ret