Stacken/c64-livecoding
6
0
Fork 0
Code Issues 1 Pull requests Projects Releases Packages Wiki Activity Actions

make line_down draw from other end of line. Reduses one CMP instruction

Browse source
This commit is contained in:
hugova 2025-07-17 13:49:09 +02:00
parent 54fa061342
commit f64d28168b
1 changed files with 24 additions and 18 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

42
wip-hugo/routines/line/line_down.s
View file

@ -73,27 +73,34 @@ selfmod:
LDA V + 1
STA case_1 + 7
end_selfmod:
LDA X_end
STA X_pos
LDA Y_end
STA Y_pos
JSR pixel_calc ;;only used first pixel. after this relative position is abused
STA byte_to_paint
;; X = X_end - X_pos
LDX dx
Sub_16 btp_mem_pos, btp_mem_pos + 1, #$00, #$00,! ;; Y has always a offset of at least 1 = C + $0000
INY
for_x:
;; Paints A to address in |btp_mem_pos* + Y|
;; Y is pixel position in the chunk. Therefor it may be that Y = 0, 1, 2, 3, 4, ,5 ,6 ,7.
LDA byte_to_paint ;A byte containing a single 1. Coresponds to X position in the chunk.
ORA (btp_mem_pos), Y
STA (btp_mem_pos), Y
increment_pixel_x:
LSR byte_to_paint ; Rotates the pixel one bit to the left ON THE SCREEN.
BCC increment_pixel_x_end; We need to move to the next chunk
move_8px_left:
;; Restores byte to paint to #%10000000
ROR byte_to_paint
decrement_pixel_x:
ASL byte_to_paint ; Rotates the pixel one bit to the left ON THE SCREEN.
BCC decrement_pixel_x_end; We need to move to the next chunk
move_8px_right:
;; Restores byte to paint to #%00000001
ROL byte_to_paint
;; Next chunk is 8 addresses away. Look in pixel_draw for more detail.
;; -8.
;; C = 1 therefore you se 07
Add_16 btp_mem_pos, btp_mem_pos + 1, #$08, #$00, !
increment_pixel_x_end:
;; C = 0
Sub_16 btp_mem_pos, btp_mem_pos + 1, #$07, #$00, !
decrement_pixel_x_end:
DEX
BEQ end ;We keep track on when to stop line draw with the X registry.
;;If D < %00000010 00000000: case_2
@ -105,20 +112,19 @@ case_1:
;; C =1 so we can use !
;; A = >D
Sub_16_A D, D + 1, #>V, #<V, !
increment_y_pos:
INY ; Increment Y pos inside the buffer
CPY #$08
decrement_y_pos:
DEY ; Increment Y pos inside the buffer
BNE for_x
move_8px_down: ; Z=1 --> C=1
LDY #$00
move_8px_up: ; Z=1 --> C=1
LDY #$08
;; Switch to chunk bellow
; C = 1
; So we subtract #$3F, #$01 +C
Add_16 btp_mem_pos, btp_mem_pos + 1, #$3F, #$01, !; +320
; So we subtract #$40, #$01
Sub_16 btp_mem_pos, btp_mem_pos + 1, #$40, #$01, !; +320
JMP for_x
increment_y_pos_end:
decrement_y_pos_end:
case_2:
Add_16 D, D + 1, #>dy_2, #<dy_2, ! ;D = D + 2*dy
Add_16 D, D + 1, #>dy_2, #<dy_2,! ;D = D + 2*dy
JMP for_x
end:
RTS