你如何移动 LibGDX 中的形状？

Question

I am currently trying to move a shape using an arrow key press in LibGDX. This is what I have so far:

    shapeRenderer.setColor(Color.BLACK);
    shapeRenderer.begin(ShapeRenderer.ShapeType.Filled);
    shapeRenderer.rect(250,250,20,20);
    if(Gdx.input.isKeyPressed(Input.Keys.LEFT)) {
        shapeRenderer.rect(200,250,20,20);

    }
    shapeRenderer.end()

However it seems to only create a new shape, as opposed to move my old one. Is there a way to move the old one with shapes, or should I be using another class?

Answer 1

ShapeRenderer only renders points, lines, "shapes" that you tell it to draw. It doesn't actually store/create shapes itself. Your code renders a rectangle every time, and if the Left key is pressed will simply draw a 2nd rectangle at slightly different coords.

If you simply want to use shapes, look at the libGDX Rectangle class itself (there are also Circle, Ellipse, Polygon classes). You can create a rectangle (assign x/y coords, width/height, etc) and then use the shape renderer to draw that rectangle based on the rectangle's x/y coords (or width/height/etc).

That's a simplistic solution, but may be all you need

Answer 2

You'll need to clear the screen between the two render calls. This can be done with the command:

Gdx.gl.glClearColor( 1, 0, 0, 1 );
Gdx.gl.glClear( GL20.GL_COLOR_BUFFER_BIT | GL20.GL_DEPTH_BUFFER_BIT );

(from the libgdx wiki).

In an actual game, this is generally done in the render method, before anything is drawn.

It is important to note that the 'shape' you have created cannot be modified at all, and most programs will shape objects (such as Rectangle) to track attributes, and then use this data in a render method. I would recommend working your way through the 'a simple game' tutorial on the libgdx wiki, it shows how a number of common game-related tasks are accomplished using libGDX. Link to tutorial.

Answer 3

It's a very bad option, but it does what you want

    ScreenUtils.clear(0, 0, 0.2f, 1);
    //camera.update();
    shapeRenderer.begin(ShapeRenderer.ShapeType.Line);
    shapeRenderer.setColor(Color.GOLD);
    if (Gdx.input.isKeyPressed(Input.Keys.LEFT)) {
        x = x + -1;
        shapeRenderer.rect(x, y, 20, 20);
    }
    if (Gdx.input.isKeyPressed(Keys.RIGHT)){
        x = x + 1;
        shapeRenderer.rect(x, y, 20, 20);
    }
    a = x;
    b = y;
    shapeRenderer.rect(a, y, 20, 20);
    shapeRenderer.end();