Rectangle collision detection system not working

Question

I made this rectangle collision system for a simple game I'm working on, but it's not working properly. It only registers a collision when the bottom left pixel of the player collides with the object, and I can't figure out why. Thanks in advance for any help.

public static boolean collision(int playerX, int playerY, int playerWidth, int playerHeight,
        int obstacleX, int obstacleY, int obstacleWidth, int obstacleHeight){

    if (coordinateWithinRect(playerX, playerY, obstacleX,
            obstacleY, obstacleWidth, obstacleHeight)) {
        return true;
    } else if (coordinateWithinRect(playerX - playerWidth,
            playerY, obstacleX, obstacleY, obstacleWidth,
            obstacleHeight)) {
        return true;
    } else if (coordinateWithinRect(playerX - playerWidth,
            playerY + playerHeight, obstacleX, obstacleY,
            obstacleWidth, obstacleHeight)) {
        return true;
    } else if (coordinateWithinRect(playerX, playerY
            + playerHeight, obstacleX, obstacleY, obstacleWidth,
            obstacleHeight)) {
        return true;
    } else {
        return false;
    }
}


private static boolean coordinateWithinRect(int xCoord, int yCoord, int xRect, int yRect, int width, int height) {
    if (xCoord > xRect && xCoord < (xRect + width) && yCoord < yRect && yCoord > (yRect - height)) {
        return true;
    } else {
        return false;
    }
}

Answer 1

In your function coordinateWithinRect you specify a width and height for your obstacle but not for your player. Is this intentional, I mean your player does not have any dimensions or they are not considered important?

Anyway, judging by the general idea of your definition of collision, I guess player is considered to collide with obstacle when it's inside the rectangle of obstacle, right? So, you should check if

• playerX is inside obstacleX-obstacleWidth/2 and obstacleX+obstacleWidth/2 while
• playerY is inside obstacleY-obstacleHeight/2 and obstacleY+obstacleHeight/2 at the same time.

Your function should be:

private static boolean coordinateWithinRect(int xPunkt, int yPunkt, int xRect, int yRect, int bredd, int höjd) {
    if (playerX > (obstacleX-obstacleWidth/2) && playerX < (obstacleX+obstacleWidth/2) && playerY > (obstacleY-obstacleHeight/2) && playerY < (obstacleY+obstacleHeight/2)) {
        return true;
    } else {
        return false;
    }
}

You don't make these checks so sure you have something wrong here or am I missing something?

Answer 2

I managed to fix the code myself, I will explain the issue and fix below incase anyone ever has the same or similar issue.

The problem lied in the fact that I had used the idea of a regular 2d coordinate system, where X increases to the right, and Y increases upwarads. In java it is the opposite. The fixed code can be seen below:

public static boolean collision(int playerX, int playerY, int playerWidth, int playerHeight,
        int obstacleX, int obstacleY, int obstacleWidth, int obstacleHeight){

    if (coordinateWithinRect(playerX, playerY, obstacleX,
            obstacleY, obstacleWidth, obstacleHeight)) {
        return true;
    } else if (coordinateWithinRect(playerX + playerWidth,
            playerY, obstacleX, obstacleY, obstacleWidth,
            obstacleHeight)) {
        return true;
    } else if (coordinateWithinRect(playerX + playerWidth,
            playerY - playerHeight, obstacleX, obstacleY,
            obstacleWidth, obstacleHeight)) {
        return true;
    } else if (coordinateWithinRect(playerX, playerY
            - playerHeight, obstacleX, obstacleY, obstacleWidth,
            obstacleHeight)) {
        return true;
    } else {
        return false;
    }
}




private static boolean coordinateWithinRect(int xCoord, int yCoord, int xRect, int yRect, int width, int height) {
    if (xCoord > xRect && xCoord < (xRect + width) && yCoord < yRect && yCoord > (yRect - height)) {
        return true;
    } else {
        return false;
    }
}