Brownian tree: Difference between revisions

=={{header|Nim}}==

Using "bitmap.nim" created for Rosetta Bitmap task.

<lang Nim>import bitmap

import random

import nimPNG

const

Size = 400 # Area size.

MaxXY = Size - 1 # Maximum possible value for x and y.

NPart = 25_000 # Number of particles.

Background = Black # Background color.

Foreground = color(50, 150, 255) # Foreground color.

randomize()

let image = newImage(Size, Size)

image.fill(Background)

image[Size div 2, Size div 2] = Foreground

for _ in 1..NPart:

block ProcessParticle:

while true: # Repeat until the particle is freezed.

# Choose position of particle.

var x, y = rand(MaxXY)

if image[x, y] == Foreground:

continue # Not free. Try again.

# Move the particle.

while true:

# Choose a motion.

let dx, dy = rand(-1..1)

inc x, dx

inc y, dy

if x notin 0..MaxXY or y notin 0..MaxXY:

break # Out of limits. Try again.

# Valid move.

if image[x, y] == Foreground:

# Not free. Freeze the particle at its previous position.

image[x - dx, y - dy] = Foreground

break ProcessParticle # Done. Process next particle.

# Save into a PNG file.

# Unfortunately, nimPNG expects a sequence of bytes, not a sequence of colors.

# So, we have to make a copy.

var data = newSeqOfCap[byte](image.pixels.len * 3)

for color in image.pixels:

data.add([color.r, color.g, color.b])

echo savePNG24("brownian.png", data, image.w, image.h)</lang>