From 47d53ecf78919f2074d37f8d6517a31d49295535 Mon Sep 17 00:00:00 2001
From: hugova <hugova@kth.se>
Date: Mon, 24 Mar 2025 17:07:14 +0100
Subject: [PATCH] Fix performance by using pointer tricks for ADD. 20% faster
 line drawing

---
 wip-hugo/routines/line/line_down.s | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/wip-hugo/routines/line/line_down.s b/wip-hugo/routines/line/line_down.s
index 7082617..b7ffead 100644
--- a/wip-hugo/routines/line/line_down.s
+++ b/wip-hugo/routines/line/line_down.s
@@ -53,15 +53,12 @@
 
         LDY #$00
         jsr pixel_draw ;;only used first pixel. after this relative position is abused
-
-;;From line_test_time this is at  program_start + list_file_offset = $080D + $0116 = $0923
 for_x:
-        ;; Lets increment btp_mem_pos with +8
-        ;; Read more in pixel_draw to understand this!
-        LDX #$00
+        ;; Paints A to address i btp_mem_pos* + Y
+        ;; Y is our Y-pos-chunk-offset.
         LDA byte_to_paint
-        ORA (>btp_mem_pos, X)
-        STA (>btp_mem_pos, X)
+        ORA (>btp_mem_pos), Y
+        STA (>btp_mem_pos), Y
 increment_pixel_x:
         CLC
         ROR byte_to_paint
@@ -84,7 +81,7 @@ increment_pixel_x_end:
 case_1:; C =1 so we can use !
         Sub_16 >D, <D, >V, <V, ! ; D = D - V
 increment_y_pos:
-        Add_16 >btp_mem_pos, <btp_mem_pos, #$01, #$00
+        ;Add_16 >btp_mem_pos, <btp_mem_pos, #$01, #$00
         INY
         CPY #$08 ;
         BEQ move_8px_down
@@ -92,7 +89,7 @@ increment_y_pos:
 move_8px_down: ; Z=1 --> C=1
         ;; +320-8 bytes
         LDY #$00
-        Add_16 >btp_mem_pos, <btp_mem_pos,#$38 , #$01
+        Add_16 >btp_mem_pos, <btp_mem_pos,#$40, #$01
         jmp for_x
 increment_y_pos_end:
 case_2: ;; C =0 because LAG_16 so we can use !