Java绘图颜色随机颜色？

Question

Well I've read some code and came across this:

private int[] tiles = new int [64 * 64];

Thats the tiles array.

And that sets a random colors to the tiles array.

    for (int i = 0; i < 64 * 64; i++) {
        this.tiles[i] = rand.nextInt(0xffffff);
    }

And now rendering

public void render() {
    for (int i = 0; i < this.height; i++) {
        for (int j = 0; j < this.width; j++) {
            int index = (j / 50) * 64;
            pixels[j + i * this.width] = tiles[index];
        }
    }
}

(Rendering outside of that class, but it doesnt matter).

Output:

but if I change j / 50 to j / 16, the tiles gets smaller and becomes this:

Why does this happen? after all the variable index only gets the color from the array? why does it make it big? j changes everytime, shouldnt the colors be different everytime?

Can someone explain this please? I am kinda confused.

Thanks!

Answer 1

It is calculating an index into the list of colours, you have only created 64 different random colours.

The loop works out the index of which of those 64 colours to use by converting the x co-ordinate into the index using (j / 50) * 64 .

Because j is an integer j/50 will give you steps, 0-49 becomes 0, 50-99 becomes 1, etc.

When you then multiply by 64 you are still keeping those steps.

If you change the divide from being a 50 to being a 16 then you are making the steps 16 pixels wide rather than 50 pixels wide.

Just be careful that you don't run off the edge of your random colours array!