在python中绘制彩色棋盘格

Question

i need to draw a colored checkers grid in an existing image, with colors taken from a list. This is the code i have:

import image as im
def draw_gen_checkers(img, s, colors):
    n = 0
    for i in range(len(img)/s):
        for j in range(len(img[0])/s):
            for ii in range(i*s, i*s+s):
                for jj in range(j*s,j*s+s):
                    img[ii][jj] = colors[n]
            if n == len(colors)-1:
                n = 0
            else:
                n = n + 1
    im.visd(img)

img = im.create(300, 200, (0,0,0))
colors = [(255,128,0),(0,0,255),(0,255,0),(255,0,0)]
s = 25

With this code this is the result i get: Image1

When the image should look like this: Image

Ty all in advance!

Answer 1

Glad to see your work progress :)

Let's do the math : your picture is 300px long, your cases are 25px long, so you have 12 cases per line, since you have 4 colors you have 12 // 4 == 3 color rotations by line, but since 12 % 3 == 0, when you start your new line, your n is back to 0. And nowhere you say that you want an increasing offset for colors in each line, so all your lines are the same.

Just adding an increment at the start of each line should do the trick.

For your n increment, instead of using an if-else people often use the modulo operator n = (n+1) % len(colors) # 0, 1, 2, 3, 0, 1, ...

edit: when I said 'adding an increment at the start of each line' I was thinking of something like that (i think it should be good):

def draw_gen_checkers(img, s, colors):
    n = 0 # Alternatively n = len(colors)
    for i in range(len(img)/s):
        n = (n + 1) % len(colors)
        for j in range(len(img[0])/s):
            for ii in range(i*s, i*s+s):
                for jj in range(j*s,j*s+s):
                    img[ii][jj] = colors[n]
            n = (n + 1) % len(colors)

The drawback would be that the first color you use will be the second in your list since it increments n before everything else. Depending on what you do it could be a problem or not, if it is you can initialize n to len(colors)-1 to fix it.

I would also create a function draw_square(i, j, s, c), with your 2 most inner loops, that would make the code more readable and more modular (this function would probably be useful somewhere else at some point).

Answer 2

def draw_gen_checkers(img, s, colors):
n = 0
for i in range(len(img)/s + 1):
    for j in range(len(img[0])/s + 1):
        for ii in range(i*s, i*s+s):
            for jj in range(j*s,j*s+s):
                if 0 <= ii < len(img) and 0 <= jj < len(img[0]):
                    img[ii][jj] = colors[n]
        n = (n+1) % len(colors)
im.visd(img)

img = im.create(300, 200, (0,0,0))
colors = [(255,128,0),(0,0,255),(0,255,0),(255,0,0)]
s = 25

It prints: img