java - 在 libgdx 中渲染 box2d

Question

我有一个使用 FitViewport 的大小为 800x480 的游戏世界，并且最初使用像素渲染 box2d 实体 + 固定装置，因此所有物理效果都显得 float 且缓慢。查看文档后，我意识到 box2d 使用度量单位，因此我将 box2d 位置和大小进行了 32 倍的转换，最终得到了 25x15 米的 box2d 世界。

我遇到的问题是，现在 box2d 对象渲染得非常小。如何缩小它们以便它们在屏幕上显示为正常尺寸？

Answer 1

您需要使用 world 和 box2 之间的转换因子。

在你的 create() 中你将拥有:

private OrthographicCamera camera;
private BodyDef bodyDef;
private Body body;
private PolygonShape box;
static float WORLD_TO_BOX, BOX_TO_WORLD, bodyWidth, bodyHieght;

public Create(){
    //Conversion factors
    WORLD_TO_BOX = 1/32f;  
    BOX_TO_WORLD = 1/WORLD_TO_BOX;

    //Creation of the camera with your factor 32
    camera = new OrthographicCamera();
    camera.viewportHeight = Gdx.graphics.getHeight() * WORLD_TO_BOX;  
    camera.viewportWidth = Gdx.graphics.getWidth() * WORLD_TO_BOX;  
    camera.position.set(camera.viewportWidth/2, camera.viewportHeight/2, 0f);  
    camera.update();  

    //Let's say you want to create a body in the center of your screen
    BodyDef = new BodyDef();  
    BodyDef.position.set(new Vector2(camera.viewportWidth/2, -camera.viewportHeight/2));  
    body = world.createBody(BodyDef);  
    box = new PolygonShape();  
    //Let's say you want your body to have the shape of a square which sides size is one fifth of your camera width
    bodyWidth = camera.viewportWidth/10;
    bodyHeight = camera.viewportWidth/10;
    box.setAsBox(bodyWidth, bodyHeight);
    body.createFixture(box, 0.0f);
} 

目前您仅使用转换系数 WORLD_TO_BOX 来创建相机。但如果你想在你的 body 上绘制一些 Sprite ，你将在 render() 中使用 BOX_TO_WORLD 因子。例如，您想使用 spritebatch 在正方形上绘制一个 Sprite ，并具有精确的大小和位置，在 render() 中您将拥有:

private Texture texture;

public void render(){
    game.batch.begin();
    game.batch.setColor(1,1,1,1);
//In Box2D, the orgin of a body is the center of the body, 
//while in your world the orgin of a sprite is the bottom left corner
//I Box2D the width and the height of a body will be twice the values you entered,
//while in your world the width and the height of a sprite are the exact values you entered.
//Taking all this into account, to draw a sprite above a body you need to :
//1 - center the sprite above the body. Ex : (body.getPosition().x - bodyWidth) for the X position
//2 - draw the sprite at the right size, taking in account the factor 2. Ex : bodyWidth * 2 for the widht of the sprite
//3 - Apply the BOX_TO_WORLD factor to all every sizes and distances
    game.batch.draw(texture,
                    BOX_TO_WORLD * (body.getPosition().x - bodyWidth),
                    BOX_TO_WORLD * (body.getPosition().y - bodyHeight),
                    BOX_TO_WORLD * bodyWidth * 2,
                    BOX_TO_WORLD * bodyHeight * 2);
     game.batch.end();
}

希望它能回答您的问题。