From 0940d9f9f91852e02da5883531e0822952a0fc61 Mon Sep 17 00:00:00 2001
From: hugova <hugova@kth.se>
Date: Sun, 2 Mar 2025 16:51:55 +0100
Subject: [PATCH] 1. A fix for a bug where D gets the wrong initial value (2
 bytes where flipped) 2. Implemented line drawing for the other 3 cases

---
 wip-hugo/routines/memory/line_down.s     | 14 ++--
 wip-hugo/routines/memory/line_down_inv.s | 87 ++++++++++++++++++++++++
 wip-hugo/routines/memory/line_up.s       | 85 +++++++++++++++++++++++
 wip-hugo/routines/memory/line_up_inv.s   | 85 +++++++++++++++++++++++
 wip-hugo/source.s                        |  2 +-
 5 files changed, 263 insertions(+), 10 deletions(-)
 create mode 100644 wip-hugo/routines/memory/line_down_inv.s
 create mode 100644 wip-hugo/routines/memory/line_up.s
 create mode 100644 wip-hugo/routines/memory/line_up_inv.s

diff --git a/wip-hugo/routines/memory/line_down.s b/wip-hugo/routines/memory/line_down.s
index 6ced07d..0c8a4fa 100644
--- a/wip-hugo/routines/memory/line_down.s
+++ b/wip-hugo/routines/memory/line_down.s
@@ -1,12 +1,11 @@
 ;;drawing line from 2 cordinates
 .proc line
-    ;;#  (X_pos, Y_pos)                                 #
+    ;;#  (X_pos, Y_pos)                                     #
     ;;#                     *                               #
     ;;#                         *                           #
     ;;#                             *                       #
     ;;#                                (X_end, Y_end)       #
-    ;;
-    ;;NOTE THAT X_pos <= X_end and line is going downwords   max 45deg!
+    ;;NOTE THAT X_pos <= X_end, Y_pos <= Y_end. Max 45deg!
 
     ;;Not values but register position in memory
     X_end = $04
@@ -53,10 +52,9 @@
     STA >D
     LDA <dy_2
     STA <D
-    Add_16 >D, <D, #$01, #$00
+    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
@@ -77,11 +75,9 @@ for_x:
     BEQ case_2
 case_1:
     INC Y_pos
-    ;; D = D - 2*dx
-    Sub_16 >D, <D, >dx_2, <dx_2
+    Sub_16 >D, <D, >dx_2, <dx_2; D = D - 2*dx
 case_2:
-    ;;D = D + 2*dy
-    Add_16 >D, <D, >dy_2, <dy_2
+    Add_16 >D, <D, >dy_2, <dy_2;D = D + 2*dy
 last:
     JMP for_x
 end:
diff --git a/wip-hugo/routines/memory/line_down_inv.s b/wip-hugo/routines/memory/line_down_inv.s
new file mode 100644
index 0000000..dfb8774
--- /dev/null
+++ b/wip-hugo/routines/memory/line_down_inv.s
@@ -0,0 +1,87 @@
+;;drawing line from 2 cordinates
+.proc line
+    ;;#  (X_pos, Y_pos)                                     #
+    ;;#                     *                               #
+    ;;#                         *                           #
+    ;;#                             *                       #
+    ;;#                                (X_end, Y_end)       #
+    ;;NOTE THAT X_pos <= X_end, Y_pos <= Y_end. Min 45deg!
+
+    ;;Not values but register position in memory
+    X_end = $04
+    Y_end = $05
+    X_pos = $FC
+    Y_pos = $FB
+    dx_2 = $0607
+    dy = $08
+    D = $0a0b
+
+    ;;Set values
+    LDA #$00
+    STA $FD ; for pixel_draw
+
+    ;example values ~~~~~ SHOULD BE PRECOMPILED
+    LDA #$00
+    STA X_pos
+    STA Y_pos
+
+    LDA #$40
+    STA X_end
+    LDA #$a0
+    STA Y_end
+    ;;~~~~~~~~~~
+
+    ;;2*dx = 2*(X_end -X_pos)
+    LDA X_end
+    SEC
+    SBC X_pos
+    STA >dx_2
+    LDA #$00
+    STA <dx_2
+    mult_16 >dx_2, <dx_2
+
+    ;;dy = (Y_end -Y_pos)
+    LDA Y_end
+    SEC
+    SBC Y_pos
+    STA dy
+
+    ;;D = 2*dx - dy + 2*255. 0 <=D <= 4*255
+    ;;Our D is bigger then wikipedia to not use negative numbers
+    LDA >dx_2
+    STA >D
+    LDA <dx_2
+    STA <D
+    Add_16 >D, <D, #$00, #$01
+    Sub_16 >D, <D, dy, #$00
+
+
+    ;;We wont use dy, only 2*dy from now on
+    dy_2 = $0809 ;Lets reuse dy register ($08)
+    LDA #$00
+    STA <dy_2
+    mult_16 >dy_2, <dy_2
+
+for_y:
+    jsr pixel_draw
+    ;;Increment Y until Y_pos = Y_end and X_pos = X_end
+    INC Y_pos
+    LDY Y_pos
+    CPY Y_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:
+    INC X_pos
+    ;; D = D - 2*dx
+    Sub_16 >D, <D, >dy_2, <dy_2
+case_2:
+    ;;D = D + 2*dy
+    Add_16 >D, <D, >dx_2, <dx_2
+last:
+    JMP for_y
+end:
+.endproc
diff --git a/wip-hugo/routines/memory/line_up.s b/wip-hugo/routines/memory/line_up.s
new file mode 100644
index 0000000..f3587df
--- /dev/null
+++ b/wip-hugo/routines/memory/line_up.s
@@ -0,0 +1,85 @@
+;;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
diff --git a/wip-hugo/routines/memory/line_up_inv.s b/wip-hugo/routines/memory/line_up_inv.s
new file mode 100644
index 0000000..861d571
--- /dev/null
+++ b/wip-hugo/routines/memory/line_up_inv.s
@@ -0,0 +1,85 @@
+;drawing line from 2 cordinates
+.proc line
+    ;;#                                      (X_pos, Y_pos) #
+    ;;#                                   *                 #
+    ;;#                         *                           #
+    ;;#                *                                    #
+    ;;# (X_end, Y_end)                                      #
+   ;;NOTE THAT Y_pos <= Y_end, X_pos >= X_end. Min 45deg!
+
+    ;;Not values but register position in memory
+    X_end = $04
+    Y_end = $05
+    X_pos = $FC
+    Y_pos = $FB
+    dx_2 = $0607
+    dy = $08
+    D = $0a0b
+
+    ;;Set values
+    LDA #$00
+    STA $FD ; for pixel_draw
+
+    ;example values ~~~~~ SHOULD BE PRECOMPILED
+    LDA #$60
+    STA X_pos
+    STA Y_pos
+
+    LDA #$50
+    STA X_end
+    LDA #$90
+    STA Y_end
+    ;;~~~~~~~~~~
+
+    ;;2*dx = 2*(X_pos - X_end)
+    LDA X_pos
+    SEC
+    SBC X_end
+    STA >dx_2
+    LDA #$00
+    STA <dx_2
+    mult_16 >dx_2, <dx_2
+
+    ;;dy = (Y_end -Y_pos)
+    LDA Y_end
+    SEC
+    SBC Y_pos
+    STA dy
+
+    ;;D = 2*dx - dy + 2*255. 0 <=D <= 4*255
+    ;;Our D is bigger then wikipedia to not use negative numbers
+    LDA >dx_2
+    STA >D
+    LDA <dx_2
+    STA <D
+    Add_16 >D, <D, #$00, #$01
+    Sub_16 >D, <D, dy, #$00
+
+
+    ;;We wont use dy, only 2*dy from now on
+    dy_2 = $0809 ;Lets reuse dy register ($08)
+    LDA #$00
+    STA <dy_2
+    mult_16 >dy_2, <dy_2
+
+for_y:
+    jsr pixel_draw
+    ;;Increment Y until Y_pos = Y_end and X_pos = X_end
+    INC Y_pos
+    LDY Y_pos
+    CPY Y_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 X_pos
+    Sub_16 >D, <D, >dy_2, <dy_2; D = D - 2*dx
+case_2:
+    Add_16 >D, <D, >dx_2, <dx_2;D = D + 2*dy
+last:
+    JMP for_y
+end:
+.endproc
diff --git a/wip-hugo/source.s b/wip-hugo/source.s
index 0434167..21017ef 100755
--- a/wip-hugo/source.s
+++ b/wip-hugo/source.s
@@ -1,6 +1,6 @@
 .include "STARTUP.s"
 .include "macros/16aritmatic.s"
-.include "routines/memory/line_down.s"
+.include "routines/memory/line_up_inv.s"
 
 loop_:
 jmp loop_