mirror of
https://github.com/fluencelabs/assemblyscript
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49 lines
1.8 KiB
TypeScript
49 lines
1.8 KiB
TypeScript
// see: https://en.wikipedia.org/wiki/Mandelbrot_set
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/** Number of discrete color values on the JS side. */
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const NUM_COLORS = 2048;
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/** Computes a single line in the rectangle `width` x `height`. */
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export function computeLine(y: u32, width: u32, height: u32, limit: u32): void {
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var translateX = width / 1.6;
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var translateY = height / 2.0;
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var scale = 10.0 / min(3 * width, 4 * height);
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var imaginary = (y - translateY) * scale;
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for (let x: u32 = 0; x < width; ++x) {
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let real = (x - translateX) * scale;
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// Iterate until either the escape radius or iteration limit is exceeded
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let ix = 0.0, iy = 0.0, ixSq: f64, iySq: f64;
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let iteration: u32 = 0;
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while ((ixSq = ix * ix) + (iySq = iy * iy) <= 4.0) {
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let ixNew = ixSq - iySq + real;
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iy = 2.0 * ix * iy + imaginary;
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ix = ixNew;
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if (iteration >= limit) break;
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++iteration;
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}
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// Do a few extra iterations for quick escapes to reduce error margin
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for (let minIterations = min(8, limit); iteration < minIterations; ++iteration) {
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let ixNew = ix * ix - iy * iy + real;
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iy = 2.0 * ix * iy + imaginary;
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ix = ixNew;
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}
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// Iteration count is a discrete value in the range [0, limit] here, but we'd like it to be
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// normalized in the range [0, 2047] so it maps to the gradient computed in JS.
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// see also: http://linas.org/art-gallery/escape/escape.html
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let frac = Math.log(Math.log(Math.sqrt(ix * ix + iy * iy))) / Math.LN2;
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let icol = isFinite(frac)
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? <u32>((NUM_COLORS - 1) * clamp((iteration + 1 - frac) / limit, 0.0, 1.0))
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: NUM_COLORS - 1;
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store<u16>((y * width + x) << 1, icol);
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}
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}
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/** Clamps a value between the given minimum and maximum. */
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@inline
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function clamp<T>(value: T, minValue: T, maxValue: T): T {
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return min(max(value, minValue), maxValue);
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}
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