From 364ef3e55c61607591c665fe77e42ca5a926e2a0 Mon Sep 17 00:00:00 2001
From: Irmen de Jong <irmen@razorvine.net>
Date: Sun, 30 Aug 2020 23:50:31 +0200
Subject: [PATCH] tweak cx16 mandelbrots

---
 compiler/res/prog8lib/cx16textio.p8 |  7 +++----
 examples/cx16/mandelbrot-gfx.bas    | 31 +++++++++++++++++++++++++++++
 examples/cx16/mandelbrot-gfx.p8     | 15 ++++++++++----
 3 files changed, 45 insertions(+), 8 deletions(-)
 create mode 100644 examples/cx16/mandelbrot-gfx.bas

diff --git a/compiler/res/prog8lib/cx16textio.p8 b/compiler/res/prog8lib/cx16textio.p8
index e20813128..1279658c8 100644
--- a/compiler/res/prog8lib/cx16textio.p8
+++ b/compiler/res/prog8lib/cx16textio.p8
@@ -30,7 +30,8 @@ asmsub  fill_screen (ubyte char @ A, ubyte txtcolor @ Y) clobbers(A)  {
 	    bne  +
 	    lda  #147       ; clear screen
 	    jmp  c64.CHROUT
-+       brk         ; TODO fill screen with another character than space....
++       ; TODO fill the screen with a different fillchar (not space) - not yet supported
+        rts
         }}
 
 }
@@ -118,9 +119,7 @@ asmsub  print_b  (byte value @ A) clobbers(A,Y)  {
 		jsr  c64.CHROUT
 +		pla
 		jsr  conv.byte2decimal
-		jsr  print_ub._print_byte_digits
-		plx
-		rts
+		jmp  print_ub._print_byte_digits
 	}}
 }
 
diff --git a/examples/cx16/mandelbrot-gfx.bas b/examples/cx16/mandelbrot-gfx.bas
new file mode 100644
index 000000000..d896e6970
--- /dev/null
+++ b/examples/cx16/mandelbrot-gfx.bas
@@ -0,0 +1,31 @@
+100 REM MANDELBROT GFX - BASIC VERSION FOR COMMANDERX16
+110 REM MANDELBROT COORDINATES
+120 XL=-2.000:XU=0.500
+130 YL=-1.100:YU=1.100
+140 MI%=16 :REM MAXIMUM ITERATIONS
+150 WI%=256:HI%=200 :REM SCREEN DIMENSIONS
+160 DX=(XU-XL)/WI%
+170 DY=(YU-YL)/HI%
+200 SCREEN $80:TI$="000000"
+500 REM MAIN LOOP
+520 X0=0:Y0=0:GOSUB2000
+530 FOR YY=0 TO HI%-1
+540 Y0=YL+DY*YY
+610 FOR XX=0 TO WI%-1
+620 X0=XL+DX*XX
+700 REM CALCULATE MANDELBROT
+710 X=0:Y=0:IT%=0
+720 X2=0:Y2=0
+730 XY=X*Y
+740 X=X2-Y2+X0
+750 Y=2*XY+Y0
+760 IT%=IT%+1
+770 X2=X*X:Y2=Y*Y
+780 IF (X2+Y2 <= 4) AND (IT% < MI%) THEN GOTO 730
+790 PSET XX,YY,MI%-IT%
+800 NEXT XX
+810 GOSUB2000
+820 NEXT YY
+1000 GOTO 1000
+2000 REM OUTPUT TIME SPENT
+2010 PRINT CHR$(19)SPC(33)TI$:RETURN
diff --git a/examples/cx16/mandelbrot-gfx.p8 b/examples/cx16/mandelbrot-gfx.p8
index eaa63a1da..2c8ff99b4 100644
--- a/examples/cx16/mandelbrot-gfx.p8
+++ b/examples/cx16/mandelbrot-gfx.p8
@@ -5,7 +5,7 @@
 main {
     const uword width = 256
     const uword height = 200
-    const ubyte max_iter = 32
+    const ubyte max_iter = 16       ; 32 looks pretty nice
 
     sub start()  {
         initialize()
@@ -16,18 +16,24 @@ main {
     }
 
     sub mandel() {
+        const float XL=-2.000
+        const float XU=0.500
+        const float YL=-1.100
+        const float YU=1.100
+        float dx = (XU-XL)/width
+        float dy = (YU-YL)/height
         ubyte pixelx
         ubyte pixely
 
         for pixely in 0 to height-1 {
-            float yy = (pixely as float)/0.35/height - 1.35
+            float yy = YL+dy*pixely
 
             cx16.r0 = 0
             cx16.r1 = pixely
             cx16.FB_cursor_position()
 
             for pixelx in 0 to width-1 {
-                float xx = (pixelx as float)/0.3/width - 2.2
+                float xx = XL+dx*pixelx
 
                 float xsquared = 0.0
                 float ysquared = 0.0
@@ -61,7 +67,8 @@ main {
         txt.plot(32, 9)
         txt.print("floats")
         txt.plot(32, 10)
-        txt.print("32 iter")
+        txt.print_b(max_iter)
+        txt.print(" iter")
 
         cx16.r0 = 0
         cx16.r1 = 0