85 lines
1.7 KiB
ArmAsm
85 lines
1.7 KiB
ArmAsm
;;drawing line from 2 cordinates
|
|
.proc line
|
|
;;# * (X_end, Y_end) #
|
|
;;# #
|
|
;;# * #
|
|
;;# * #
|
|
;;# (X_pos, Y_pos) #
|
|
;;
|
|
;;NOTE THAT X_pos <= X_end, Y_pos >= Y_end. Max 45deg!
|
|
|
|
;;Not values but register position in memory
|
|
X_end = $04
|
|
Y_end = $05
|
|
X_pos = $FC
|
|
Y_pos = $FB
|
|
dy_2 = $0607
|
|
dx = $08
|
|
D = $0a0b
|
|
|
|
;;Set values
|
|
LDA #$00
|
|
STA $FD ; for pixel_draw
|
|
|
|
;example values ~~~~~ SHOULD BE PRECOMPILED
|
|
LDA #$90
|
|
STA X_pos
|
|
STA Y_pos
|
|
|
|
LDA #$aa
|
|
STA X_end
|
|
LDA #$80
|
|
STA Y_end
|
|
;;~~~~~~~~~~
|
|
|
|
;;2*dy = 2*(Y_pos-Y_end)
|
|
LDA Y_pos
|
|
SEC
|
|
SBC Y_end
|
|
STA >dy_2
|
|
LDA #$00
|
|
STA <dy_2
|
|
mult_16 >dy_2, <dy_2
|
|
|
|
;;dx = (X_end -X_pos)
|
|
LDA X_end
|
|
SEC
|
|
SBC X_pos
|
|
STA dx
|
|
|
|
;;D = 2*dy - dx + 2*255. 0 <=D <= 4*255
|
|
;;Our D is bigger then wikipedia to not use negative numbers
|
|
LDA >dy_2
|
|
STA >D
|
|
LDA <dy_2
|
|
STA <D
|
|
Add_16 >D, <D, #$00, #$01
|
|
Sub_16 >D, <D, dx, #$00
|
|
|
|
;;We wont use dx, only 2*dx from now on
|
|
dx_2 = $0809 ;Lets reuse dx register ($08)
|
|
LDA #$00
|
|
STA <dx_2
|
|
mult_16 >dx_2, <dx_2
|
|
|
|
for_x:
|
|
jsr pixel_draw
|
|
;;Increment X until X_pos = X_end and Y_pos = Y_end
|
|
INC X_pos
|
|
LDX X_pos
|
|
CPX X_end
|
|
BEQ end
|
|
|
|
;;If D < %00000001 11111111 <==> >D ==0, then: case_2
|
|
LDA <D; if <D > 0 then: case_1
|
|
CMP #$00
|
|
BEQ case_2
|
|
case_1:
|
|
DEC Y_pos
|
|
Sub_16 >D, <D, >dx_2, <dx_2; D = D -2*dx
|
|
case_2:
|
|
Add_16 >D, <D, >dy_2, <dy_2;D = D + 2*dy
|
|
last:
|
|
JMP for_x
|
|
end:
|
|
.endproc
|