fractal effect is cooking

[dosdemo] / src / fract.c

diff --git a/src/fract.c b/src/fract.c
new file mode 100644 (file)
index 0000000..0245b72
--- /dev/null
+++ b/src/fract.c
@@ -0,0 +1,151 @@
+#include <string.h>
+#include <limits.h>
+#include "demo.h"
+#include "screen.h"
+#include "gfxutil.h"
+
+struct vec2x {
+       long x, y;
+};
+
+static int init(void);
+static void destroy(void);
+static void draw(void);
+static int julia(long x, long y, long cx, long cy, int max_iter);
+static int calc_walk(struct vec2x *path, long x, long y, int max_steps);
+
+static struct screen scr = {
+       "fract",
+       init,
+       destroy,
+       0, 0,
+       draw
+};
+
+static long aspect_24x8 = (long)(1.3333333 * 256.0);
+static long xscale_24x8 = (long)(1.3333333 * 1.2 * 256.0);
+static long yscale_24x8 = (long)(1.2 * 256.0);
+static int cx, cy;
+static int max_iter = 50;
+
+#define WALK_SIZE      20
+
+struct screen *fract_screen(void)
+{
+       return &scr;
+}
+
+static int init(void)
+{
+       return 0;
+}
+
+static void destroy(void)
+{
+}
+
+#define PACK_RGB16(r, g, b) \
+       (((((r) >> 3) & 0x1f) << 11) | ((((g) >> 2) & 0x3f) << 5) | (((b) >> 3) & 0x1f))
+
+static void draw(void)
+{
+       int i, j, len, x, y;
+       unsigned short *pixels = fb_pixels;
+       struct vec2x walkpos[WALK_SIZE];
+
+       cx = mouse_x;
+       cy = mouse_y;
+
+       for(i=0; i<fb_height; i++) {
+               for(j=0; j<fb_width; j++) {
+                       unsigned char pidx = julia(j, i, cx, cy, max_iter) & 0xff;
+                       *pixels++ = (pidx >> 3) | ((pidx >> 2) << 5) | ((pidx >> 3) << 11);
+               }
+       }
+
+       pixels = fb_pixels;
+
+       if((len = calc_walk(walkpos, mouse_x, mouse_y, WALK_SIZE))) {
+               x = walkpos[0].x >> 16;
+               y = walkpos[0].y >> 16;
+
+               for(i=1; i<len; i++) {
+                       int x0 = x;
+                       int y0 = y;
+                       int x1 = walkpos[i].x >> 16;
+                       int y1 = walkpos[i].y >> 16;
+
+                       if(clip_line(&x0, &y0, &x1, &y1, 0, 0, fb_width - 1, fb_height - 1)) {
+                               draw_line(x0, y0, x1, y1, PACK_RGB16(32, 128, 255));
+                       }
+                       x = x1;
+                       y = y1;
+               }
+       }
+
+       pixels[mouse_y * fb_width + mouse_x] = 0xffe;
+}
+
+static long normalize_coord(long x, long range)
+{
+       /* 2 * x / range - 1*/
+       return (x << 17) / range - 65536;
+}
+
+static long device_coord(long x, long range)
+{
+       /* (x + 1) / 2 * (range - 1) */
+       return ((x + 65536) >> 1) * (range - 1);
+}
+
+static int julia(long x, long y, long cx, long cy, int max_iter)
+{
+       int i;
+
+       /* convert to fixed point roughly [-1, 1] */
+       x = (normalize_coord(x, fb_width) >> 8) * xscale_24x8;
+       y = (normalize_coord(y, fb_height) >> 8) * yscale_24x8;
+       cx = (normalize_coord(cx, fb_width) >> 8) * xscale_24x8;
+       cy = (normalize_coord(cy, fb_height) >> 8) * yscale_24x8;
+
+       for(i=0; i<max_iter; i++) {
+               /* z_n = z_{n-1}**2 + c */
+               long px = x >> 8;
+               long py = y >> 8;
+
+               if(px * px + py * py > (4 << 16)) {
+                       break;
+               }
+               x = px * px - py * py + cx;
+               y = (px * py << 1) + cy;
+       }
+
+       return i < max_iter ? (256 * i / max_iter) : 0;
+}
+
+static int calc_walk(struct vec2x *path, long x, long y, int max_steps)
+{
+       int i;
+       long cx, cy;
+
+       /* convert to fixed point roughly [-1, 1] */
+       x = cx = (normalize_coord(x, fb_width) >> 8) * xscale_24x8;
+       y = cy = (normalize_coord(y, fb_height) >> 8) * yscale_24x8;
+
+       for(i=0; i<max_steps; i++) {
+               /* z_n = z_{n-1}**2 + c */
+               long px = x >> 8;
+               long py = y >> 8;
+
+               path[i].x = device_coord((x << 8) / xscale_24x8, fb_width);
+               path[i].y = device_coord((y << 8) / yscale_24x8, fb_height);
+
+               if(px * px + py * py > (4 << 16)) {
+                       break;
+               }
+               x = px * px - py * py + cx;
+               y = (px * py << 1) + cy;
+       }
+
+       return i;
+}