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- **************************************
- *** DRAW SLICE LINE ***
- **************************************
- Draw_Slice_Line
- *send x1,y1,x2,y2 in d0,d1,d2,d3
- *bitmap in a0
- ext.l d0
- ext.l d1
- *make copies
- move.w d0,d4
- move.w d1,d5
- move.w #-1,d7
-
- sub.w d2,d0 ;deltax
- beq draw_horiz_line
- bpl.s do_y ;is line going left to right
- neg.w d0 ;make deltax positive
- move.w #1,d7 ;xinc
- do_y
- sub.w d3,d1 ;deltay
- beq draw_vert_line
- bmi.s line_going_down
- neg.w d7 ;neg xinc
- move.w d2,d4 ;swap x start value
- move.w d3,d5 ;swap y start value
- bra.s test_major
- line_going_down
- neg.w d1 ;make y delta positive
- test_major
- *Calculate start position in bitmap
- mulu #BPR,d5
- move.w d4,d6
- lsr.w #3,d6
- add.w d6,d5
- add.l d5,a0 ;start pos
- andi.w #$7,d4 ;start pixel pos
- neg.w d4
- add.w #7,d4
-
- cmp.w d1,d0
- blt.s y_major
- x_major
- move.w d7,d5 ;x inc
- *get x step value
- divu d1,d0 ;divide deltax by deltay
- move.w d1,d7
- move.w d0,d2 ;get x step value
- subq.w #1,d2
- swap d0 ;error step
- move.w d1,d3
- lsr d3 ;error value
- neg d3
- subq.w #1,d1
-
- x_delta_loop
- move.w d2,d6 ;loop value
- add.w d0,d3
- blt.s x_step_loop
- addq.w #1,d6 ;extra pixel
- sub.w d7,d3 ;reset error value
- x_step_loop
- bset d4,(a0) ;set pix
- sub.w d5,d4 ;add direction to x
- bge.s not_dropped_left
- addq.l #1,a0
- moveq.w #7,d4
- dbra d6,x_step_loop
- add.l #BPR,a0
- dbra d1,x_delta_loop
- rts
- not_dropped_left
- cmp.w #8,d4
- bne.s do_xloop
- subq.l #1,a0
- clr.w d4
- do_xloop
- dbra d6,x_step_loop
- finished_x_loop
- add.l #BPR,a0
- dbra d1,x_delta_loop
- rts
-
- y_major
- move.w d7,d5 ;get x inc
- *get x step value
- divu d0,d1 ;divide deltay by deltax
- move.w d0,d7
- move.w d1,d2 ;get x step value
- subq.w #1,d2
- swap d1 ;error step
- move.w d0,d3
- lsr d3 ;error value
- neg d3
- subq.w #1,d0
-
- y_delta_loop
- move.w d2,d6 ;loop value
- add.w d1,d3
- blt.s y_step_loop
- addq.w #1,d6 ;extra pixel
- sub.w d7,d3 ;reset error value
- y_step_loop
- bset d4,(a0)
- add.l #BPR,a0
- dbra d6,y_step_loop
- sub.w d5,d4 ;add x
- bge.s y_x_not_dropped
- addq.l #1,a0
- moveq.w #7,d4
- dbra d0,y_delta_loop
- rts
- y_x_not_dropped
- cmp.w #8,d4
- bne.s do_y_loop
- subq.l #1,a0
- clr.w d4
- do_y_loop
- dbra d0,y_delta_loop
- rts
-
- draw_horiz_line
- rts
- draw_vert_line
- rts
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