101 lines
2.5 KiB
ArmAsm
101 lines
2.5 KiB
ArmAsm
;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
|
|
|
|
;;drawing line from 2 cordinates
|
|
;;# * (X_end, Y_end) #
|
|
;;# #
|
|
;;# * #
|
|
;;# * #
|
|
;;# (X_pos, Y_pos) #
|
|
;;
|
|
;;NOTE THAT X_pos <= X_end, Y_pos >= Y_end. Max 45deg!
|
|
|
|
.proc line_up
|
|
.include "line.inc"; Defines memory positions, ex X_pos
|
|
|
|
;LDA #$20
|
|
;STA X_pos
|
|
;STA Y_pos
|
|
;LDA #$10
|
|
;STA Y_end
|
|
;LDA #$40
|
|
;STA X_end
|
|
|
|
|
|
;;We need to clear this memory
|
|
LDA #$00
|
|
STA <V
|
|
STA <dy_2
|
|
STA $FD ; for pixel_draw
|
|
|
|
;; V = 2*(dx -dy)
|
|
;; where: dy = Y_end - Y_start, dx = OO - X_start
|
|
LDA Y_pos
|
|
SEC
|
|
SBC Y_end
|
|
STA >V
|
|
STA >dy_2; >dy_2 = dy. Needed for dy_2 (not for V)
|
|
LDA X_end
|
|
SEC
|
|
SBC X_pos
|
|
STA dx
|
|
SEC
|
|
SBC >V
|
|
STA >V; <V = dx - dy
|
|
mult_16 >V, <V; V = 2*(dx -dy)
|
|
|
|
;dy_2 = dy*2
|
|
mult_16 >dy_2, <dy_2, !
|
|
;; D = 2*dy - dx
|
|
;; In loop we have that D = D -V
|
|
;; So D needs to be at least >=V.
|
|
;; V_max = 00000001 11111111
|
|
;; For us to work with unsigned numbers we add 00000001 11111111
|
|
;; to V and the branch logic to V!
|
|
|
|
;;D = 2*dy - dx + 2*255
|
|
;;Our D is bigger then wikipedia because D is unsigned.
|
|
LDA >dy_2
|
|
STA >D
|
|
LDA <dy_2
|
|
STA <D
|
|
Add_16 >D, <D, #$ff, #$01, !
|
|
Sub_16 >D, <D, dx, #$00
|
|
|
|
jsr pixel_draw
|
|
;INY ; Dont want underflow
|
|
;LDY #$09
|
|
;Sub_16 >btp_mem_pos, <btp_mem_pos, #$40, #$01 ;-320
|
|
LDX X_pos
|
|
for_x:
|
|
LDA byte_to_paint
|
|
ORA (>btp_mem_pos), Y
|
|
STA (>btp_mem_pos), Y
|
|
increment_pixel_x:
|
|
LSR byte_to_paint
|
|
BCC increment_pixel_x_end
|
|
move_8px_left:
|
|
Add_16 >btp_mem_pos, <btp_mem_pos, #$08, #$00
|
|
LDA #%10000000
|
|
STA byte_to_paint
|
|
increment_pixel_x_end:
|
|
INX
|
|
CPX X_end
|
|
BEQ end
|
|
Lag_16 >D, <D, #$00, #$02, case_2
|
|
case_1:
|
|
Sub_16 >D, <D, >V, <V
|
|
decrement_y_pos:
|
|
DEY
|
|
CPY #$ff
|
|
BNE for_x
|
|
move_8px_up:
|
|
LDY #$07
|
|
Sub_16 >btp_mem_pos, <btp_mem_pos, #$40, #$01 ;-320
|
|
jmp for_x
|
|
decrement_y_pos_end:
|
|
case_2:
|
|
Add_16 >D, <D, >dy_2, <dy_2 ;D = D + 2*dy
|
|
JMP for_x
|
|
end:
|
|
RTS
|
|
.endproc
|