ww/examples/mandelbrot/mandelbrot.ww

// mandelbrot — ANSI-color Mandelbrot set, printed via libc.
//
// What this proves:
//   1. ww does f64 arithmetic (mul, add, sub, div) end to end.
//   2. The @symbol FFI mechanism binds write() from libc.so.6.
//   3. w6l's dynamic linker (PT_INTERP + PT_DYNAMIC + PLT/GOT) reaches
//      a real .so at runtime — `ldd mandelbrot` shows libc.so.6 as a
//      NEEDED entry.
//
// Each pixel is a colored space rendered via xterm 256-color background
// escapes (\e[48;5;Nm). We use libc's `write` (a thin syscall wrapper)
// rather than `putchar` because the runtime here doesn't call
// __libc_start_main, so stdio state stays uninitialised and putchar's
// buffer is never flushed.
//
// Build: see ./Makefile. No cc — pure ww toolchain.

package mandelbrot;

@symbol("write") fn c_write(fd: i32, buf: *void, n: u64) i64;

def W:    i32 = 78;
def H:    i32 = 30;
def MAXI: i32 = 80;

// Number of iterations before |z| escapes |z|>2, capped at MAXI.
fn iterate(cr: f64, ci: f64) i32 = {
	let zr: f64 = 0.0;
	let zi: f64 = 0.0;
	let i:  i32 = 0;
	for (i < MAXI) {
		let zr2: f64 = zr * zr;
		let zi2: f64 = zi * zi;
		if (zr2 + zi2 > 4.0) { return i; };
		let nz: f64 = zr2 - zi2 + cr;
		zi = (2.0 * zr) * zi + ci;
		zr = nz;
		i += 1;
	};
	return MAXI;
};

// Pick an xterm-256 color for an escape count. Inside the set is black;
// outside cycles blue → cyan → green → yellow → red.
fn palette(n: i32) i32 = {
	if (n >= MAXI) { return 16; };	// black, inside set
	let q: i32 = (n * 12) / MAXI;
	if (q ==  0) { return  17; };	// dark blue
	if (q ==  1) { return  18; };
	if (q ==  2) { return  19; };
	if (q ==  3) { return  21; };	// bright blue
	if (q ==  4) { return  33; };
	if (q ==  5) { return  45; };
	if (q ==  6) { return  51; };	// cyan
	if (q ==  7) { return  50; };
	if (q ==  8) { return  46; };	// green
	if (q ==  9) { return 154; };
	if (q == 10) { return 226; };	// yellow
	if (q == 11) { return 208; };	// orange
	return 196;			// red
};

// Write `n` as decimal into buf at off; return new offset.
fn writedec(buf: *u8, off: i32, n: i32) i32 = {
	if (n == 0) { buf[off] = '0': u8; return off + 1; };
	let tmp: [4]u8;
	let v:   i32 = n;
	let i:   i32 = 0;
	for (v > 0) {
		tmp[i] = ((v % 10) + 48): u8;
		v = v / 10;
		i += 1;
	};
	let cnt: i32 = i;
	let j:   i32 = 0;
	for (j < cnt) {
		i -= 1;
		buf[off + j] = tmp[i];
		j += 1;
	};
	return off + cnt;
};

// Emit "\e[48;5;<color>m " (set background + the pixel) into buf.
fn emitcell(buf: *u8, off: i32, color: i32) i32 = {
	buf[off + 0] = 27u8;
	buf[off + 1] = '[': u8;
	buf[off + 2] = '4': u8;
	buf[off + 3] = '8': u8;
	buf[off + 4] = ';': u8;
	buf[off + 5] = '5': u8;
	buf[off + 6] = ';': u8;
	let p: i32 = writedec(buf, off + 7, color);
	buf[p + 0] = 'm': u8;
	buf[p + 1] = ' ': u8;
	return p + 2;
};

// Emit "\e[0m\n" — restore default colors, end the row.
fn emitendrow(buf: *u8, off: i32) i32 = {
	buf[off + 0] = 27u8;
	buf[off + 1] = '[': u8;
	buf[off + 2] = '0': u8;
	buf[off + 3] = 'm': u8;
	buf[off + 4] = 10u8;	// '\n'
	return off + 5;
};

export fn main() i32 = {
	// Classic Mandelbrot window. The y range is squashed to W/H so
	// the picture looks roughly proportional in a terminal cell.
	let xmin: f64 = -2.5;
	let xmax: f64 =  1.0;
	let ymin: f64 = -1.1;
	let ymax: f64 =  1.1;
	let dx:   f64 = (xmax - xmin) / (W: f64);
	let dy:   f64 = (ymax - ymin) / (H: f64);

	// Each pixel is ~12 bytes (\e[48;5;NNNm ); plus 5 for the reset
	// + newline. 2048 bytes per row is comfortably above the worst
	// case of W=78.
	let row: [2048]u8;
	let y:   i32 = 0;
	for (y < H) {
		let ci:  f64 = ymin + (y: f64) * dy;
		let off: i32 = 0;
		let x:   i32 = 0;
		for (x < W) {
			let cr: f64 = xmin + (x: f64) * dx;
			let n:  i32 = iterate(cr, ci);
			off = emitcell(row.ptr, off, palette(n));
			x += 1;
		};
		off = emitendrow(row.ptr, off);
		c_write(1, row.ptr: *void, off: u64);
		y += 1;
	};
	return 0;
};