#!/usr/bin/env python3

import png
import numpy as np
import random

size = 512
num_layers = 32
density = 1000

# Blade properties
dmax = 30                # Max horizontal bending
n_exp = 2                # Grade of the exponential function that describes the blade
min_height = 16          # Minimum height in layers

texels = np.zeros((size, size, num_layers), dtype=np.int)

for i in range(0, density):
    # Fill the base layer. The rest of the layers are computed from it
    x = random.randint(0, size-1)
    y = random.randint(0, size-1)
    texels[y, x, 0] = 1

    direction = random.randint(0, 3) # 4 directions
    height = random.randint(min_height, num_layers)
    factor = random.random();
    for layer in range(1, num_layers):
        # Exit loop when we reach the blade height
        if layer > height:
            break

        d = ((dmax*pow(layer, n_exp))/pow(num_layers, n_exp))*factor
        d = int(d) # To integer

        new_x = x;
        new_y = y;
        if direction == 0:
            new_x = x+d
        elif direction == 1:
            new_x = x-d
        elif direction == 2:
            new_y = y+d
        elif direction == 3:
            new_y = y-d

        # Discard out of bounds pixels
        if new_x >= 0 and new_x < size and new_y >= 0 and new_y < size:
            texels[new_y, new_x, layer] = 1

# Encode in decimal
image = np.zeros((size, size, 4), dtype=np.int)
for y in range(0, size):
    for x in range(0, size):
        curr = np.flipud(texels[y, x])
        split_curr = np.split(curr, 4)

        for channel in reversed(range(0, 4)):
            out = 0
            for bit in split_curr[channel]:
                out = (out << 1) | bit

            image[y, x, channel] = out

png.from_array(image.tolist(), 'RGBA').save("grass_density.png")