From efac8f4f621d11698caa69f2f6ea57aabc106408 Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Sun, 22 Jan 2023 09:09:12 -0800
Subject: [PATCH] now writes pixels sorta

---
 mandel.s | 37 +++++++++++++++++++------------------
 1 file changed, 19 insertions(+), 18 deletions(-)

diff --git a/mandel.s b/mandel.s
index 5cf1e9a..8a963d6 100644
--- a/mandel.s
+++ b/mandel.s
@@ -18,6 +18,12 @@ zoom  = $a1     ; u8: zoom shift level
 temp  = $a2     ; u16
 temp2 = $a4     ; u16
 
+pixel_ptr    = $b0 ; u16
+pixel_color  = $b2 ; u8
+pixel_mask   = $b3 ; u8
+pixel_shift  = $b4 ; u8
+pixel_offset = $b5 ; u8
+
 ; FP registers in zero page
 FR0 = $d4
 FRE = $da
@@ -108,8 +114,8 @@ bit_masks:
     .byte 3 << 6
 
 display_list_start:
-    ; 48 lines overscan
-    .repeat 5
+    ; 24 lines overscan
+    .repeat 3
         .byte $70 ; 8 blank lines
     .endrep
 
@@ -185,8 +191,8 @@ color_map:
 
 .macro shl bytes, arg
     asl arg
-    .repeat bytes-1
-        rol arg
+    .repeat bytes-1, i
+        rol arg + 1 + i
     .endrepeat
 .endmacro
 
@@ -525,12 +531,6 @@ enough:
     ; iter holds the target to use
     ; @todo implement
 
-    pixel_ptr    = $b0
-    pixel_color  = $b2
-    pixel_mask   = $b3
-    pixel_shift  = $b4
-    pixel_offset = $b5
-
     ; iter -> color
     ldx iter
     lda color_map,x
@@ -563,7 +563,7 @@ point:
     ;    temp * 40
     ; =  temp * 32  +  temp * 8
     ; = (temp << 5) + (temp << 3)
-    extend_8_16 temp, sy
+    copy16 temp, sy
     shl16 temp
     shl16 temp
     shl16 temp
@@ -588,6 +588,9 @@ point:
 shift_loop:
     beq shift_done
     asl pixel_color
+    asl pixel_color
+    sec
+    rol pixel_mask
     sec
     rol pixel_mask
     dex
@@ -602,11 +605,10 @@ shift_done:
     tay
 
     ; read, mask, or, write
-    lda (temp),y
+    lda (pixel_ptr),y
     and pixel_mask
     ora pixel_color
-    lda #255
-    sta (temp),y
+    sta (pixel_ptr),y
 
     rts
 .endproc
@@ -703,13 +705,12 @@ loop_sx:
     zoom_factor cx, sx, zoom, aspect_x
     zoom_factor cy, sy, zoom, aspect_y
     ;jsr mandelbrot
-    lda #1
+    lda #2
     sta iter
     jsr pset
 
-
-    lda sx
     clc
+    lda sx
     adc #1
     sta sx
     lda sx + 1
@@ -723,8 +724,8 @@ loop_sx:
 
 loop_sx_done:
 
-    lda sy
     clc
+    lda sy
     adc #1
     sta sy
     lda sy + 1