fox32rom/draw_pixel.asm

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2022-04-17 01:13:16 +02:00
; generic pixel drawing routines
; draw a pixel to a framebuffer
; inputs:
; r0: X coordinate
; r1: Y coordinate
; r2: color
; r3: pointer to framebuffer
; r4: framebuffer width (pixels)
; outputs:
; none
draw_pixel_generic:
push r0
push r1
push r3
push r4
; calculate pointer to the framebuffer
mul r4, 4 ; 4 bytes per pixel
mul r1, r4 ; y * width * 4
mul r0, 4 ; x * 4
add r0, r1 ; y * width * 4 + (x * 4)
add r3, r0
mov r0, r3 ; r0: pointer to framebuffer
mov [r0], r2
pop r4
pop r3
pop r1
pop r0
ret