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Mandelbrot: Implement color smoothing with gradients

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This removes the color banding that happens for some of the
"outer" areas which all have the same iteration count.
This commit is contained in:
Gunnar Beutner 2021-05-17 17:01:05 +02:00 • committed by Andreas Kling
parent c961616e6d
commit b429ee88f8
1 changed files with 20 additions and 5 deletions
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23
Userland/Demos/Mandelbrot/Mandelbrot.cpp
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@ -45,7 +45,7 @@ public:
calculate(); calculate();
} }
i32 mandelbrot(double px, double py, i32 max_iterations) double mandelbrot(double px, double py, i32 max_iterations)
{ {
// Based on https://en.wikipedia.org/wiki/Plotting_algorithms_for_the_Mandelbrot_set // Based on https://en.wikipedia.org/wiki/Plotting_algorithms_for_the_Mandelbrot_set
const double x0 = px * (m_x_end - m_x_start) / m_bitmap->width() + m_x_start; const double x0 = px * (m_x_end - m_x_start) / m_bitmap->width() + m_x_start;
@ -64,15 +64,30 @@ public:
iteration++; iteration++;
} }
if (iteration == max_iterations)
return iteration; return iteration;
auto lz = sqrt(x * x + y * y) / 2;
return 1 + iteration + log(lz / log(2)) / log(2);
}
static double linear_interpolate(double v0, double v1, double t)
{
return v0 + t * (v1 - v0);
} }
void calculate_pixel(int px, int py, int max_iterations) void calculate_pixel(int px, int py, int max_iterations)
{ {
auto iterations = mandelbrot(px, py, max_iterations); auto iterations = mandelbrot(px, py, max_iterations);
double hue = (double)iterations * 360.0 / (double)max_iterations; auto whole_iterations = floor(iterations);
if (hue == 360.0) auto partial_iterations = fmod(iterations, 1);
hue = 0.0; double hue1 = whole_iterations * 360.0 / max_iterations;
if (hue1 >= 360.0)
hue1 = 0.0;
double hue2 = (whole_iterations + 1) * 360.0 / max_iterations;
if (hue2 >= 360.0)
hue2 = 0.0;
double hue = linear_interpolate(hue1, hue2, partial_iterations);
double saturation = 1.0; double saturation = 1.0;
double value = iterations < max_iterations ? 1.0 : 0; double value = iterations < max_iterations ? 1.0 : 0;
m_bitmap->set_pixel(px, py, Color::from_hsv(hue, saturation, value)); m_bitmap->set_pixel(px, py, Color::from_hsv(hue, saturation, value));