add another part of the circle. now 1/4 circle done

wip-hugo/routines/circle/circle.inc

@@ -7,3 +7,7 @@
         t2    = $E1
         X_rel = radius
         Y_rel = $E3
+        temp = $E4
+        temp_ = $E7
+        btp_mem_pos_center = $E5 ;; 16bit <fix>
+        btp_mem_pos_inv = $EE    ;; 16bit <fix>

wip-hugo/routines/circle/circle.s

@@ -19,16 +19,71 @@
         LSR
         STA t1
 
+
+draw_center_px_in_circle:
+        JSR  pixel_draw
+        LDA btp_mem_pos
+        STA btp_mem_pos_center
+        LDA btp_mem_pos + 1
+        STA btp_mem_pos_center + 1
+        ;; btp_mem_pos_center_two = 2*btp_mem_pos_center | used later for calculating btp_mem_pos_inv
+        btp_mem_pos_center_two = btp_mem_pos_center
+        Mult_16 btp_mem_pos_center, btp_mem_pos_center + 1
+
+
+draw_right_px_in_circle:
+        CLC
+        LDA X_pos
+        ADC radius
+        STA X_pos
         ;; We only draw the first pixel using absolute position.
         ;; After that we use relative position.
         JSR pixel_draw
         ;; This sets byte_to_paint, btp_mem_pos and Y
+
 while_x_bigger_then_y:
 
+;STY temp
+;LDY #$00
+draw_pixel:
         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
 
+draw_pixel_inv:
+        SEC
+        LDA btp_mem_pos_center_two
+        SBC btp_mem_pos
+        STA btp_mem_pos_inv
+        LDA btp_mem_pos_center_two + 1
+        SBC btp_mem_pos + 1
+        STA btp_mem_pos_inv + 1
+
+;; calculate the inverted y value Y = 7-Y
+STY temp
+LDA #$07
+SEC
+SBC temp
+TAY
+
+;; calculate byte_to_paint_inv (could be faster with lookup table)
+        LDA byte_to_paint
+        STA temp_
+        LDA #%10000000
+        jmp start_calc
+calc:
+        LSR A
+start_calc:
+        LSR temp_
+BCC calc
+
+; A = byte_to_paint_inv
+        ORA (btp_mem_pos_inv), Y
+        STA (btp_mem_pos_inv), Y
+
+;;Recover the Y value (we changed it because evrything is inverted)
+ldy temp
+
 increment_y_pos:
         INC Y_rel ; y++
         INY

wip-hugo/routines/circle/circle_test.s

@@ -3,7 +3,7 @@
         LDA #$50
         STA X_pos
         STA Y_pos
-        LDA #$55
+        LDA #$35
         STA radius
         JSR circle
 .endscope