Chase player with camera in AndEngine and limit world's bounds

问题

Using AndEngine for Android, I would like to have my scene look like this:

The red box is the world which must be limited to a given size, say 2000px*450px.

The blue box is the Camera, which is limited as well (as usual), for example to 750px*450px.

For the whole scene, I have a background image that is exactly 450px high. So my Camera can be scaled to whatever size is appropriate, but the background must exactly fit to the height. The width of the Camera may be variable.

The player (circle) must always be in the center (horizontally) but may not leave the world's boundaries.

To achieve this, I've tried adding two types of sizes:

camera size (CAMERA_WIDTH, CAMERA_HEIGHT)
world size (WORLD_WIDTH, WORLD_HEIGHT)

And this function was to add boundaries to the world so that the physics engine prevents the player from leaving those boundaries:

private void createWorldBoundaries() {
    Body body;
    final Rectangle wall_top = new Rectangle(0, WORLD_HEIGHT-5, WORLD_WIDTH, 10, mVertexManager);
    final Rectangle wall_bottom = new Rectangle(0, 5, WORLD_WIDTH, 10, mVertexManager);
    final Rectangle wall_left = new Rectangle(5, 0, 10, WORLD_HEIGHT, mVertexManager);
    final Rectangle wall_right = new Rectangle(WORLD_WIDTH-5, 0, 10, WORLD_HEIGHT, mVertexManager);
    body = PhysicsFactory.createBoxBody(mPhysicsWorld, wall_top, BodyType.StaticBody, new PhysicsFactory.createFixtureDef(0.0f, 0.5f, 0.5f));
    wall_top.setUserData(body);
    body = PhysicsFactory.createBoxBody(mPhysicsWorld, wall_bottom, BodyType.StaticBody, new PhysicsFactory.createFixtureDef(0.0f, 0.5f, 0.5f));
    wall_bottom.setUserData(body);
    body = PhysicsFactory.createBoxBody(mPhysicsWorld, wall_left, BodyType.StaticBody, new PhysicsFactory.createFixtureDef(0.0f, 0.5f, 0.5f));
    wall_left.setUserData(body);
    body = PhysicsFactory.createBoxBody(mPhysicsWorld, wall_right, BodyType.StaticBody, new PhysicsFactory.createFixtureDef(0.0f, 0.5f, 0.5f));
    wall_right.setUserData(body);
    attachChild(wall_top);
    attachChild(wall_bottom);
    attachChild(wall_left);
    attachChild(wall_right);
}

~~But this is not working, unfortunately.~~ (see edit)

Setting the camera to chase the player has the wrong result for me: The player does really stay in the center of the screen all time, but I want the player only to stay in the center horizontally, not vertically.

What am I doing wrong and what can I change? And the basic question is: How can I make the world wider than the camera view, while the height is equal to the camera view. The result should be that you can horizontally walk through your world (moving camera) and you can always see the full height.

Edit:

As you define the coordinates of the Rectangle's center and not its top-left corner, you have to do it like this, it seems:

final Rectangle wall_top = new Rectangle(WORLD_WIDTH/2, WORLD_HEIGHT-1, WORLD_WIDTH, 2, mVertexManager);
final Rectangle wall_bottom = new Rectangle(WORLD_WIDTH/2, FIELD_BASELINE_Y+1, WORLD_WIDTH, 2, mVertexManager);
final Rectangle wall_left = new Rectangle(1, WORLD_HEIGHT/2, 2, WORLD_HEIGHT, mVertexManager);
final Rectangle wall_right = new Rectangle(WORLD_WIDTH-1, WORLD_HEIGHT/2, 2, WORLD_HEIGHT, mVertexManager);

However, I had found the other solution in several tutorials. Are these authors not testing their code before writing the tutorials or did the behaviour change from GLES1 to GLES2 or with any recent version?

回答1:

i think your question about the world boundaries is self answered, isn't it?

PhysicsWorld Boundaries

for further research you can download nicolas' AndEngine Examples App from the Play Store and look up the different examples here (GLES_2, didn't look for AnchorCenter yet): https://github.com/nicolasgramlich/AndEngineExamples/tree/GLES2/src/org/andengine/examples

Taken from the PhysicsExample, the code for the rectangles should look like this, if the bounds are set to the camera bounds. in your case, you can extend width like you want (3 times CAMERA_WIDTH?)

    final Rectangle ground = new Rectangle(0, CAMERA_HEIGHT - 2, WORLD_WIDTH, 2, vertexBufferObjectManager);
    final Rectangle roof = new Rectangle(0, 0, WORLD_WIDTH, 2, vertexBufferObjectManager);
    final Rectangle left = new Rectangle(0, 0, 2, CAMERA_HEIGHT, vertexBufferObjectManager);
    final Rectangle right = new Rectangle(WORLD_WIDTH - 2, 0, 2, CAMERA_HEIGHT, vertexBufferObjectManager);

Camera following player for the Camera to follow your player, you can lookup the code of the BoundCameraExample https://github.com/nicolasgramlich/AndEngineExamples/blob/GLES2/src/org/andengine/examples/BoundCameraExample.java

the interesting part for you should be the addFace method at the bottom

private void addFace(final float pX, final float pY) {
    final FixtureDef objectFixtureDef = PhysicsFactory.createFixtureDef(1, 0.5f, 0.5f);
final AnimatedSprite face = new AnimatedSprite(pX, pY, this.mBoxFaceTextureRegion, this.getVertexBufferObjectManager()).animate(100);
final Body body = PhysicsFactory.createBoxBody(this.mPhysicsWorld, face, BodyType.DynamicBody, objectFixtureDef);
this.mScene.attachChild(face);
this.mPhysicsWorld.registerPhysicsConnector(new PhysicsConnector(face, body, true, true));

this.mBoundChaseCamera.setChaseEntity(face);
}

this method creates a physics body + sprite for "your player" (in this case, a boxed face) and sets the sprite as a chaseEntity for the camera to follow. Since the camera has bounds, that it can't exceed and your camera will have the height of your PhysicWorld boundaries, you can use this to let your camera follow the player in x, but not in y direction.

if you (i don't know why) don't want to use these boundaries, you can overwrite the onUpdate method of your Sprite and re-locate your camera only in x-direction, instead of xy coords

face.registerUpdateHandler(new IUpdateHandler() {
   @Override
   public void onUpdate(final float pSecondsElapsed) {
      float[] coord = face.getSceneCenterCoordinates();
      this.mBoundChaseCamera.setCenter(sceneCenterCoordinates[0], CAMERA_Y_POSITION);
   }
}

where the CAMERA_Y_POSITION is a static final field with the y-position.

I hope this answers your question(s). :-)

edit: oops, i forgot to mention, how to achieve the camera to be bound and i will edit the world width above:

    this.mBoundChaseCamera.setBounds(0, 0,
            WORLD_WIDTH, CAMERA_HEIGHT);

all settings are like your image given (except the exact position of the face, that has to be given to the addFace(px, py))

Edit: Difference between scene boundaries in Andengine GLES2 vs GLES2-AnchorCenter

As far as i understood the question, i thought you would use GLES2, i thought of the (older) default GLES2 branch of AndEngine and posted the boundaries. As you found out yourself before and stated in the comments, you use another approach to set the rectangles - where you need to set the rectangles center as pX and pY. The reason for this is in fact, that with the AnchorCenter branch, you won't set the upper left position of an entity anymore and instead use it's center position.

来源：https://stackoverflow.com/questions/17496205/chase-player-with-camera-in-andengine-and-limit-worlds-bounds

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android

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