LibGDX-播放器与平台（或图块）之间的碰撞检测，无需使用TiledMap

Question

In my game the character is constantly moving from left to right, so there will never be a situation where he hits the right side of a platform. I had a very brief talk with somebody and he suggested me to model my platform as 4 rectangles so that I would only need 3 cases in my algorithm (ie Player can only collide with the rectangles shaded green in the image below). Here's a visual description of what I mean:

I gave it a try but the collision detection is still messed up. It doesn't go through the side of the platform (this is good news since we want this to happen) but you can't glide on top of it or bounce under it. Can anyone see where I may have gone wrong?

public void checkCollisions(ArrayList<GameObject> list) {

    for (int i = 0; i < list.size(); i++) {
        for (int j = i + 1; j < list.size(); j++) {
            GameObject go1 = list.get(i);
            GameObject go2 = list.get(j);
            boolean playerPlatformCollision = go1.getType()
                    .equalsIgnoreCase("player") && go2.getType().equalsIgnoreCase("platform");
            if (playerPlatformCollision) {
              Rectangle playerRect = go1.getRect();
              Rectangle platformRect = go2.getRect();
                if (playerRect.overlaps(platformRect)) {

                    float platformRectX, platformRectY, platformRectWidth, platformRectHeight;
                    platformRectX = go2.getRect().getX(); // x position of the platform
                    platformRectY = go2.getRect().getY(); // y position of the platform
                    platformRectWidth = go2.getRect().getWidth(); // width of platform
                    platformRectHeight = go2.getRect().getHeight(); // height of platform

                    Rectangle caseA = new Rectangle(platformRectX,
                            platformRectY, platformRectX + 1,
                            platformRectHeight);
                    Rectangle caseB = new Rectangle(platformRectX + 1,
                            (platformRectY + platformRectHeight) - 1,
                            platformRectWidth - 1, platformRectHeight);
                    Rectangle caseC = new Rectangle(platformRectX + 1,
                            platformRectY, platformRectWidth, 1);

                    if (playerRect.overlaps(caseA)) {
                        go1.setxSpeed(0);
                    } else if (playerRect.overlaps(caseB)) {
                        go1.setySpeed(0);
                    } else if (playerRect.overlaps(caseC)) {
                        go1.setySpeed(-3f);
                    }
                }
            }
        }
    }
} 

Please let me know if you are not clear with any parts of the code.

Answer 1

I can't be sure that this is the issue, but it seems that this problem is not addressed in your code, and I have had similar problems myself when ignoring this. When your player collides with the platform, it means that its rectangle is already intersecting the platform, by anywhere between 1 and how fast you are going number of pixels. Just adjusting the x and y speed is not enough. You must also remove the player rectangle from the platform, or else the player will get stuck. This can be done by using a loop and checking if your player is still colliding. if so, move 1 pixel over in the direction you came from, until no longer colliding.