Water ripple algorithm not producing accurate results

Question

The sources that I used to write this code are https://web.archive.org/web/20160418004149/http://freespace.virgin.net/hugo.elias/graphics/x_water.htm and https://www.youtube.com/watch?v=BZUdGqeOD0w. The problem I'm having with the algorithm is that it often produces negative numbers, which are not valid for colour. Here is my code (I know that I shouldn't use PyGame for pixel-pushing and I plan on using OpenGL in the future):

import pygame
pygame.init()

cols = 200
rows = 200

window = pygame.display.set_mode((cols, rows))

buffer1 = [[0 for _ in range(rows)] for _ in range(cols)]
buffer2 = buffer1.copy()

buffer1[100][100] = 255         #Raindrop


dampening = 0.97


running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_ESCAPE:
                running = False

    for i in range(1, cols - 1):
        for j in range(1, rows - 1):
            buffer2[i][j] = ((buffer1[i+1][j] + buffer1[i-1][j] + buffer1[i][j+1] + buffer1[i][j-1]) / 2) - buffer2[i][j]
            buffer2[i][j] = buffer2[i][j] * dampening

    #Displaying the buffer
    for i in range(cols):
        for j in range(rows):
            window.fill((buffer2[i][j], buffer2[i][j], buffer2[i][j]), (i, j, 1, 1))

    #Swapping the buffers
    buffer1, buffer2 = buffer2, buffer1

    pygame.display.update()

pygame.display.quit()
pygame.quit()

I've been struggling with this for a while now and I'm now finally turning to you for help. Thanks in advance.

Did you see @Rabbid76's excellent answer here - https://stackoverflow.com/questions/60336688/water-ripple-effect-python-and-pygame-from-coding-train-video?rq=1 — Kingsley, Mar 05 '20 at 21:45

score 0 · Accepted Answer · answered Mar 06 '20 at 14:36

The problem I'm having with the algorithm is that it often produces negative numbers, which are not valid for colour.

I suggest to clamp the color values to the range [0, 255]. e.g:

c = max(0, min(255, buffer2[i][j]))
window.fill((c, c, c), (i, j, 1, 1))

Water ripple algorithm not producing accurate results

1 Answers1