Question

I have an image I’m drawing in java 2d but I want it to keep wrapping forever once the coordinates are outside the size of the image. The problem at the moment is that once the coordinates that I specify go outside the size of the image, it draws nothing so the image ends.

E.g an image that constantly moves horizontally and doesn’t end.

int posx = (int) ((Player.x / 20));
int posy = (int) ((Player.y / 20));
g.drawImage(SpaceBGLayer0, 0, 0, screenwidth, screenheight, posx, posy, posx+3000, posy+3000, null, null);

Answer 1

To wrap the image, you need to first test whether there’s any ‘overflow’ (ie any parts of the screen where wrapping is required). There are 4 cases: no overflow, x-overflow, y-overflow, x- and y-overflow.

Depending on the case, you may then need to draw additional copies of your image displaced by 3000px in either x, y or both.

I’ve assumed that your (posx,posy) point corresponds to the lower left corner of the screen, and that both screenWidth and screenHeight are less than 3000…

// calculate posx and posy, ensuring they lie within 0-2999:
int posx = (3000+((int)(Player.x / 20))%3000)%3000;
int posy = (3000+((int)(Player.y / 20))%3000)%3000;

// test for overflow:
boolean xOverflow = (posx+screenWidth > 3000);
boolean yOverflow = (posy+screenHeight > 3000);

// draw the image:
drawMyImage(posx,posy);
// if necessary, draw displaced copies:
if(xOverflow) drawMyImage(posx-3000,posy);
if(yOverflow) drawMyImage(posx,posy-3000);
if(xOverflow && yOverflow) drawMyImage(posx-3000,posy-3000);

...

private static void drawMyImage(int x, int y){
    int dx1 = Math.max(-x,0);
    int dy1 = Math.max(-y,0);
    int dx2 = Math.min(3000-x,screenWidth);
    int dy2 = Math.min(3000-y,screenHeight);
    int sx1 = Math.max(x,0);
    int sy1 = Math.max(y,0);
    int sx2 = Math.min(x+screenWidth,3000);
    int sy2 = Math.min(y+screenHeight,3000);
    g.drawImage(SpaceBGLayer0, dx1, dy1, dx2, dy2, sx1, sy1, sx2, sy2, null, null);
}

I haven’t tested this. You should replace all the 3000‘s with some variables, such as backgroundWidth and backgroundHeight…