A fix to a bug, to make line_down draw lines with small slopes.

I needed to use 16bit logic to ashive this.
Also moved out dx*2, dy*2 calculation outside of loop for better performance.

wip-hugo/macros/16aritmatic.s

@@ -9,13 +9,24 @@
 	STA a_hi
 .endmacro
 
+.macro Sub_16 a_low, a_hi, b_low, b_hi  ; a = a - b
+    SEC
+    LDA a_low
+    SBC b_low
+    STA a_low
+    LDA a_hi
+    SBC b_hi
+    STA a_hi
+.endmacro
+
+
 .macro mult_16 low_, hi_  ; [low, hi] = [low, hi]*2
 	CLC
 	ROL low_
 	ROL hi_
 .endmacro
 
-;
+
 ;.proc Sub_abs_8 ;return, primary, secondary
 ;	LDA primary
 ;	SEC

wip-hugo/routines/memory/line_down.s

@@ -1,6 +1,5 @@
 ;;drawing line from 2 cordinates
 .proc line
-testing:
     ;;#  (X_pos, Y_pos)                                 #
     ;;#                     *                               #
     ;;#                         *                           #
@@ -14,63 +13,76 @@ testing:
     Y_end = $05
     X_pos = $FC
     Y_pos = $FB
-    dy = $06
+    dy_2 = $0607
-    dx = $07
+    dx = $08
-    D = $08
+    D = $0a0b
 
     ;;Set values
     LDA #$00
     STA $FD ; for pixel_draw
 
-    ;;example values ~~~~~ SHOULD BE PRECOMPILED
+    ;example values ~~~~~ SHOULD BE PRECOMPILED
     LDA #$00
     STA X_pos
     STA Y_pos
 
-    LDA #$50
+    LDA #$f0
     STA X_end
-    STA dx
+    LDA #$80
-    LDA #$40
     STA Y_end
-    STA dy
+    ;;~~~~~~~~~~
-    LDA #($40 + $40 - $50 )
+
-    STA D ; = 2*dy - dx
+    ;;2*dy = 2*(Y_end -Y_pos)
-    ;; ~~~~~~~
+    LDA Y_end
+    SEC
+    SBC Y_pos
+    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, #$01, #$00
+    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
-    ;;LDY D ; FOR DEBUG
+    ;;Increment X until X_pos = X_end and Y_pos = Y_end
-    ;;If D <= 0  then: skipp
+    INC X_pos
-    LDX D;
+    LDX X_pos
-    DEX
+    CPX X_end
-    BMI case_2
+    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 Y_pos
-
+    ;; D = D - 2*dx
-    ;;D = D_before -2*dx
+    Sub_16 >D, <D, >dx_2, <dx_2
-    LDA dx
-    ROL A
-    TAX
-    LDA D
-    STX D ; D = -2*dx, A = D_before
-    SEC
-    SBC D ; A = D_before -2*dx
-    STA D;
-    jmp last
 case_2:
-    ;;D = D + 2*dx
+    ;;D = D + 2*dy
-    LDA dx
+    Add_16 >D, <D, >dy_2, <dy_2
-    ROL
-    CLC
-    ADC D
-    STA D
 last:
-    CMP #$00
-   ;;increment x untill x == large
-    INC X_pos
-    LDA X_pos
-    CMP #199
-    BEQ end
     JMP for_x
 end:
-    jmp testing
+.endproc
-   .endproc

wip-hugo/routines/memory/pixel_draw.s

@@ -1,4 +1,5 @@
 ;;Screen print. Draws a pixel at a specified position.
+;; Destroys A X Y
 .proc pixel_draw; Draws a pixel at  [Y = FB , X = FC, FD].  Y = 0 - 320, X= 0 - 200
     ;;write_byte = 00010000,
 	LDA $FC ; X (mod 8)