用python实现水纹特效

需要安装pygame模块，还需要一张背景图片，因为计算比较费时间，图片不能太大。鼠标点击处即现水纹效果。算法描述详见： http://wenku.baidu.com/view/bba633e96294dd88d0d26b7d.html

#coding=utf-8
import pygame
from sys import exit
from pygame.locals import *

BACK_WIDTH=300 #背景图宽度
BACK_HEIGHT=230 #背景图高度

pygame.init()
screen = pygame.display.set_mode((BACK_WIDTH, BACK_HEIGHT), 0, 32)

background = pygame.image.load('wave_bk.png') #读取背景图片
clock = pygame.time.Clock()

buf1 = [[0 for col in range(BACK_WIDTH)] for row in range(BACK_HEIGHT)] #振幅数组1
buf2 = [[0 for col in range(BACK_WIDTH)] for row in range(BACK_HEIGHT)] #振幅数组2

canvas = pygame.Surface((BACK_WIDTH, BACK_HEIGHT))

def update(delta):
    global buf1, buf2
    
    for row in range(1, BACK_HEIGHT - 1):
        for col in range(1, BACK_WIDTH - 1):
            buf2[row][col] = ((buf1[row][col+1]+buf1[row][col-1]+buf1[row+1][col]+buf1[row-1][col])>>1) - buf2[row][col]    #x0'=(x1+x2+x3+x4)/2-x0
            buf2[row][col] -= (buf2[row][col] >> 5) #波能衰减 1/32
                
    buf1, buf2 = buf2, buf1 # swap
        
    canvas.lock()
    for row in range(0, BACK_HEIGHT):
        for col in range(0, BACK_WIDTH):
            if row == 0 or row == BACK_HEIGHT - 1 or col == 0 or col == BACK_WIDTH - 1:
                canvas.set_at((col, row), background.get_at((col, row)))
            else:    
                #近似的用水面上某点的前后、左右两点的波幅之差来代表所看到水底景物的偏移量(模拟折射)
                xoff = buf1[row][col+1]-buf1[row][col-1]
                yoff = buf1[row+1][col]-buf1[row-1][col]
                newCol = int(col+xoff)
                newRow = int(row+yoff)
                if newCol < 0:
                    newCol = 0
                if newCol > BACK_WIDTH-1:
                    newCol = BACK_WIDTH-1
                if newRow < 0:
                    newRow = 0
                if newRow > BACK_HEIGHT-1:
                    newRow = BACK_HEIGHT-1
                canvas.set_at((col, row), background.get_at((newCol, newRow)))     
    
    canvas.unlock()  
    screen.blit(canvas, (0,0))
    
while True:
    for event in pygame.event.get():
        if event.type == QUIT:
            exit()        
        
        if event.type == MOUSEBUTTONDOWN:
            x, y = pygame.mouse.get_pos()
            buf1[y][x] = -120 #在鼠标点击位置添加能量
            
    # 帧率控制
    time_passed = clock.tick(30)
    
    update(time_passed)
       
    pygame.display.update()