gfx mandelbrot example added

examples/mandelbrot-gfx.p8

@@ -0,0 +1,51 @@
+%import c64lib
+%import c64flt
+%import c64graphics
+%zeropage floatsafe
+
+; Draw a mandelbrot in graphics mode (the image will be 256 x 200 pixels).
+; NOTE: this will take an eternity to draw on a real c64.
+; even in Vice in warp mode (700% speed on my machine) it's slow, but you can see progress
+
+main {
+    const ubyte width = 255
+    const ubyte height = 200
+    const ubyte max_iter = 16
+
+    sub start()  {
+        graphics.enable_bitmap_mode()
+
+        ubyte pixelx
+        ubyte pixely
+
+        for pixely in 0 to height-1 {
+            float yy = (pixely as float)/0.4/height - 1.0
+
+            for pixelx in 0 to width-1 {
+                float xx = (pixelx as float)/0.3/width - 2.2
+
+                float xsquared = 0.0
+                float ysquared = 0.0
+                float x = 0.0
+                float y = 0.0
+                ubyte iter = 0
+
+                while iter<max_iter and xsquared+ysquared<4.0 {
+                    y = x*y*2.0 + yy
+                    x = xsquared - ysquared + xx
+                    xsquared = x*x
+                    ysquared = y*y
+                    iter++
+                }
+
+                if iter & 1 {
+                    graphics.plotx = pixelx
+                    graphics.plot(pixely)
+                }
+            }
+        }
+
+        forever {
+        }
+    }
+}

examples/mandelbrot.p8

@@ -30,7 +30,7 @@ main {
                 float y = 0.0
                 ubyte iter = 0
 
-                while (iter<max_iter and xsquared+ysquared<4.0) {
+                while iter<max_iter and xsquared+ysquared<4.0 {
                     y = x*y*2.0 + yy
                     x = xsquared - ysquared + xx
                     xsquared = x*x