julia: add a morphing Julia set renderer

This is unoptimized, with a palette slapped together in vim, but still
pretty neat!

1 files changed, 117 insertions, 0 deletions

diff --git a/src/modules/julia/julia.c b/src/modules/julia/julia.c
new file mode 100644
index 0000000..1afb3cc
--- /dev/null
+++ b/src/modules/julia/julia.c
@@ -0,0 +1,117 @@
+#include <stdint.h>
+#include <inttypes.h>
+#include <math.h>
+
+#include "fb.h"
+#include "rototiller.h"
+
+/* Copyright (C) 2017 Vito Caputo <vcaputo@pengaru.com> */
+
+/* Julia set renderer - see https://en.wikipedia.org/wiki/Julia_set, morphing just means to vary C. */
+
+/* TODO: explore using C99 complex.h and its types? */
+
+static inline unsigned julia_iter(float real, float imag, float creal, float cimag, unsigned max_iters)
+{
+	unsigned	i;
+	float		newr, newi;
+
+	for (i = 1; i < max_iters; i++) {
+		newr = real * real - imag * imag;
+		newi = imag * real;
+		newi += newi;
+
+		newr += creal;
+		newi += cimag;
+
+		if ((newr * newr + newi * newi) > 4.0)
+			return i;
+
+		real = newr;
+		imag = newi;
+	}
+
+	return 0;
+}
+
+/* Draw a morphing Julia set */
+static void julia(fb_fragment_t *fragment)
+{
+	static uint32_t	colors[] = {
+				/* this palette is just something I slapped together, definitely needs improvement. TODO */
+				0x000000,
+				0x000044,
+				0x000088,
+				0x0000aa,
+				0x0000ff,
+				0x0044ff,
+				0x0088ff,
+				0x00aaff,
+				0x00ffff,
+				0x44ffaa,
+				0x88ff88,
+				0xaaff44,
+				0xffff00,
+				0xffaa00,
+				0xff8800,
+				0xff4400,
+				0xff0000,
+				0xaa0000,
+				0x880000,
+				0x440000,
+				0x440044,
+				0x880088,
+				0xaa00aa,
+				0xff00ff,
+				0xff4400,
+				0xff8800,
+				0xffaa00,
+				0xffff00,
+				0xaaff44,
+				0x88ff88,
+				0x44ffaa,
+				0x00ffff,
+				0x00aaff,
+				0x0088ff,
+				0xff4400,
+				0xff00ff,
+				0xaa00aa,
+				0x880088,
+				0x440044,
+
+			};
+	static float	rr;
+
+	unsigned	x, y;
+	unsigned	stride = fragment->stride / 4, width = fragment->width, height = fragment->height;
+	uint32_t	*buf = fragment->buf;
+	float		real, imag;
+	float		realstep = 3.6f / (float)width, imagstep = 3.6f / (float)height;
+
+			/* Rather than just sweeping creal,cimag from -2.0-+2.0, I try to keep things confined
+			 * to an interesting (visually) range.  TODO: could certainly use refinement.
+			 */
+	float		realscale = 0.01f * cosf(rr) + 0.01f;
+	float		imagscale = 0.01f * sinf(rr * 3.0f) + 0.01f;
+	float		creal = (1.01f + (realscale * cosf(1.5f*M_PI+rr) + realscale)) * cosf(rr * .3f);
+	float		cimag = (1.01f + (imagscale * sinf(rr * 3.0f) + imagscale)) * sinf(rr);
+
+	/* Complex plane confined to {-1.8 - 1.8} on both axis (slightly zoomed), no dynamic zooming is performed. */
+	for (imag = 1.8, y = 0; y < height; y++, imag += -imagstep) {
+		for (real = -1.8, x = 0; x < width; x++, buf++, real += realstep) {
+			*buf = colors[julia_iter(real, imag, creal, cimag, sizeof(colors) / sizeof(*colors))];
+		}
+
+		buf += stride;
+	}
+
+	rr += .01;
+}
+
+rototiller_renderer_t	julia_renderer = {
+	.render = julia,
+	.name = "julia",
+	.description = "Julia set fractal morpher",
+	.author = "Vito Caputo <vcaputo@pengaru.com>",
+	.license = "GPLv2",
+};