From b86815613888c8d1c6495db79a1f5285f6f42f95 Mon Sep 17 00:00:00 2001
From: hugova <hugova@kth.se>
Date: Thu, 10 Jul 2025 16:28:17 +0200
Subject: [PATCH] reduse zeropage usage of circle-draw

---
 wip-hugo/routines/circle/circle.inc | 41 +++++++++++++----------------
 wip-hugo/routines/circle/circle.s   | 22 ++++++++--------
 2 files changed, 29 insertions(+), 34 deletions(-)

diff --git a/wip-hugo/routines/circle/circle.inc b/wip-hugo/routines/circle/circle.inc
index 9495d4e..6e1c76a 100644
--- a/wip-hugo/routines/circle/circle.inc
+++ b/wip-hugo/routines/circle/circle.inc
@@ -6,34 +6,29 @@
 ;; private args
         t1    = $E0
         t2    = $E1
-        X_rel = radius
-        Y_rel = $E2
-        Y_copy = $E3
-        temp_ = $ED
-        jmp_location_pointer_two = $E4 ;16bit value (uses E5)
-        jmp_location_pointer = $EE ;16 bit value (uses EF)
+        X_math = radius
+        Y_math = $E2
+        jmp_location_pointer_two = $E3 ;16-bit value (uses E4)
+        jmp_location_pointer = $E5     ;16-bit value (uses E6)
+        ;; E8 - EA is used by pixel.inc
         byte_to_paint_qaa = byte_to_paint
         byte_to_paint_qcb = $EB
         byte_to_paint_qca = $EC
-
-        ; E8 - EA is used by pixel.inc
-        byte_to_paint_qdb = $CF
-        btp_mem_pos_center = $E6
-        btp_mem_pos_center_two = btp_mem_pos_center
+        byte_to_paint_qdb = $ED
 
         btp_mem_pos_qaa = btp_mem_pos
-        btp_mem_pos_qcb = $D0   ; 16bit value (uses D1)
-        btp_mem_pos_qdb = $D2 ;16bit value (uses D3)
-        btp_mem_pos_qda =$D4   ; 16bit value (uses D5)
-
-        ;;mirrord
-        btp_mem_pos_qab = $D6
-        btp_mem_pos_qca = $D8
-        btp_mem_pos_qba = $DA
-        btp_mem_pos_qbb = $DC
+        btp_mem_pos_qcb = $D0 ; 16bit value (uses D1)
+        btp_mem_pos_qdb = $D2 ; 16bit value (uses D3)
+        btp_mem_pos_qda = $D4 ; 16bit value (uses D5)
+        btp_mem_pos_qab = $D6 ; 16bit value (uses D7)
+        btp_mem_pos_qca = $D8 ; 16bit value (uses D9)
+        btp_mem_pos_qba = $DA ; 16bit value (uses DB)
+        btp_mem_pos_qbb = $DC ; 16bit value (uses DD)
 
         Y_qda = $DE
         Y_qdb = $DF
-        Y_qbb = $CE
-        temp__ = $CD
-        Y_qaa = Y_copy
+        Y_qbb = $E7 ;; <-- we use E7 here!
+        Y_qaa = $C0
+        ;;Reuse addresses, be carful here!
+        temp__ = Y_qaa
+        temp_ = Y_qda
diff --git a/wip-hugo/routines/circle/circle.s b/wip-hugo/routines/circle/circle.s
index 7a57b0b..50573ad 100644
--- a/wip-hugo/routines/circle/circle.s
+++ b/wip-hugo/routines/circle/circle.s
@@ -35,10 +35,10 @@
         STA jmp_location_pointer_two + 1
 
 
-        ;; X_rel = radius (share the same address)
-        ;;Y_rel =0
+        ;; X_math = radius (share the same address)
+        ;;Y_math =0
         LDA #$00
-        STA Y_rel
+        STA Y_math
 
         ;; t1 = radius >> 4
         LDA radius
@@ -94,7 +94,7 @@ draw_left_px_in_circle: ;similar as above
         LDA temp__
         STA X_pos
 draw_lower_px_in_circle: ;similar as above
-        CLC
+        ;; C=0 becuase pixel draw!
         LDA Y_pos
         ADC radius
         STA Y_pos
@@ -174,13 +174,13 @@ draw_qab:
         STA (btp_mem_pos_qab), Y
 
 
-;; Y_rel and X_rel is the X and Y in the eye of the algorithm. Thsese are calculated seperatly from the pixel cordinates,
+;; Y_math and X_math is the X and Y in the eye of the algorithm. Thsese are calculated seperatly from the pixel cordinates,
 ;; but are modified at the same time. This is becsuse the pixel cordinate system is complex (see pixel draw)
 
 LDY #$07 ;; Y is expected to be 7 from this point on in the loop
 
 change_Y:
-        INC Y_rel ; y++
+        INC Y_math ; y++
 qaa_y:
         DEC Y_qaa
         BPL qaa_y_end
@@ -222,11 +222,11 @@ qcb_x_end:
         ;;t1 += y
         CLC
         LDA t1
-        ADC Y_rel
+        ADC Y_math
         STA t1
         ;; t2 = t1 - x
         SEC
-        SBC X_rel
+        SBC X_math
         STA t2
         ;; if t2 < 0 then skip to endif
         ;; we can skipp CMP #$00 because SBC above do the same
@@ -234,7 +234,7 @@ qcb_x_end:
         JMP (jmp_location_pointer_two)
 if:
 change_x:
-        DEC X_rel
+        DEC X_math
         LDA t2
         STA t1    ; t1 = t2
 qaa_x:
@@ -279,8 +279,8 @@ qbb_y_end:
 
 endif:
         ;; repeat if X > Y
-        LDA X_rel
-        CMP Y_rel
+        LDA X_math
+        CMP Y_math
         BCC end
         JMP (jmp_location_pointer)
 end: