LibGDX：boundsInFrustrum 和 BoundingBox 未按预期工作答案

【问题标题】：LibGDX: boundsInFrustrum and BoundingBox not working as expectedLibGDX：boundsInFrustrum 和 BoundingBox 未按预期工作
【发布时间】：2016-03-28 16:36:23
【问题描述】：

我正在从 json 文件加载 box2d 场景。此场景包含一个固定装置，用于标记允许相机进入的边界框。使用这种机制在上下边界上工作得很好，但在上下边界上完全失败，这很奇怪。

这是从文件中加载边界框的部分：

PolygonShape shape = ((PolygonShape) fixture.getShape());
Vector2 vertex = new Vector2();
float boundLeft = world.startX, boundRight = world.startX, boundUp = world.startY, boundLow = world.startY; // The location of the camera as initial value

for (int i = 0; i < shape.getVertexCount(); i++) { // Itarate over each vertex in the fixture and set the boundary values
    shape.getVertex(i, vertex);
    vertex.add(body.getPosition());
    boundLeft = Math.min(vertex.x, boundLeft);
    boundLow = Math.min(vertex.y, boundLow);
    boundRight = Math.max(vertex.x, boundRight);
    boundUp = Math.max(vertex.y, boundUp);
}

// Build the bounding boxes with enough thickness to prevent tunneling on fast pans
world.boundLeft = new BoundingBox(new Vector3(boundLeft - 5, boundLow - 5, 0).scl(RenderingSystem.PPM), new Vector3(boundLeft, boundUp + 5, 0).scl(RenderingSystem.PPM));
world.boundRight = new BoundingBox(new Vector3(boundRight, boundLow - 5, 0).scl(RenderingSystem.PPM), new Vector3(boundRight + 5, boundUp + 5, 0).scl(RenderingSystem.PPM));
world.boundUp = new BoundingBox(new Vector3(boundLeft - 5, boundUp, 0).scl(RenderingSystem.PPM), new Vector3(boundRight + 5, boundUp + 5, 0).scl(RenderingSystem.PPM));
world.boundLow = new BoundingBox(new Vector3(boundLeft - 5, boundLow - 5, 0).scl(RenderingSystem.PPM), new Vector3(boundRight + 5, boundLow, 0).scl(RenderingSystem.PPM));
// world is a class containing some properties, including these BoundingBoxes
// RenderingSystem.PPM is the amount of pixels per metre, in this case 64

当相机平移时会调用以下部分：

public void pan(float x, float y) {
    Vector3 current = new Vector3(camera.position);
    camera.translate(-x, y);
    camera.update(true);
    if (camera.frustum.boundsInFrustum(world.boundLeft) || camera.frustum.boundsInFrustum(world.boundRight)) {
        camera.position.x = current.x; // Broke bounds on x axis, set camera back to old x
        camera.update();
    }
    if (camera.frustum.boundsInFrustum(world.boundLow) || camera.frustum.boundsInFrustum(world.boundUp)) {
        camera.position.y = current.y; // Broke bounds on y axis, set camera back to old y
        camera.update();
    }
    game.batch.setProjectionMatrix(camera.combined);
}

【问题讨论】：

你为什么不和 libdx 的人谈谈，那里有很多人抱怨这个库！
哦，我没有抱怨。 LibGDX 是我生命中的挚爱，我随时都会嫁给它，只是我通常不如 LibGDX 人聪明。

标签： java math libgdx collision-detection

【解决方案1】：

好吧，我想通了。猜猜我的 world.startx 和 world.startY 被定义为什么？没错，它们在屏幕坐标中：

world.startX = start.getPosition().x * RenderingSystem.PPM;
world.startY = start.getPosition().y * RenderingSystem.PPM;

这导致 Math.max 总是选择 world.startX 和 world.startY，因为相比之下这些值绝对是巨大的。

【讨论】：