From 1ad8071f75737a0d9d5ce8b97d46e346847f394e Mon Sep 17 00:00:00 2001
From: hugova <hugova@kth.se>
Date: Thu, 17 Jul 2025 14:00:56 +0200
Subject: [PATCH] Reduses one CMP instruction in line_down_inv by drawing the
 line in the other direction

---
 wip-hugo/routines/line/line_down_inv.s | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/wip-hugo/routines/line/line_down_inv.s b/wip-hugo/routines/line/line_down_inv.s
index d026525..f7430c1 100644
--- a/wip-hugo/routines/line/line_down_inv.s
+++ b/wip-hugo/routines/line/line_down_inv.s
@@ -49,20 +49,26 @@ 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
+        INY
+        Sub_16 btp_mem_pos, btp_mem_pos + 1, #$01, #$00
         LDX dy
 for_y:
         LDA byte_to_paint
         ORA (btp_mem_pos), Y
         STA (btp_mem_pos), Y
 increment_y_pos:
-        INY
-        CPY #$08
+        DEY
         BNE increment_y_pos_end
 move_8px_down:
-        LDY #$00
-        Add_16 btp_mem_pos, btp_mem_pos + 1, #$3F ,#$01, !
+        LDY #$08
+        Sub_16 btp_mem_pos, btp_mem_pos + 1, #$40 ,#$01
 increment_y_pos_end:
         DEX
         ;CPX Y_end
@@ -71,11 +77,11 @@ increment_y_pos_end:
 case_1:
         Sub_16_A D, D + 1, #>V, #<V, !
 increment_pixel_x:
-        LSR byte_to_paint
+        ASL byte_to_paint
         BCC for_y
 move_8px_left:
-        ROR byte_to_paint
-        Add_16 btp_mem_pos, btp_mem_pos + 1, #$08, #$00, !
+        ROL byte_to_paint
+        Sub_16 btp_mem_pos, btp_mem_pos + 1, #$08, #$00
         JMP for_y
 case_2:
         Add_16 D, D + 1, #>dx_2, #<dx_2, ! ;D = D + 2*dx