我正在使用Libgdx 引擎开发一款游戏。我必须从box2d 的身体中获取宽度和高度。他们有什么方法可以从box2d 中的主体获取宽度和高度？？
【问题讨论】：
PhysicsUtil。
我还在 gamedev.stackexchange.com 上的相同线程上发布了这个答案
我知道这是一个非常古老的线程，但我只是在这里用自己的方式获取 Body 的大小：https://github.com/Wasupmacuz/Box2DBodySize
如果链接对您来说太诡异，这里是代码：
import com.badlogic.gdx.math.Vector2;
import com.badlogic.gdx.physics.box2d.Body;
import com.badlogic.gdx.physics.box2d.ChainShape;
import com.badlogic.gdx.physics.box2d.CircleShape;
import com.badlogic.gdx.physics.box2d.EdgeShape;
import com.badlogic.gdx.physics.box2d.Fixture;
import com.badlogic.gdx.physics.box2d.PolygonShape;
import com.badlogic.gdx.physics.box2d.Shape;
/**
* Finds the size (width and height) of a body by checking its fixtures' shapes
*/
public class Sizerinator3000
{
public static Vector2 getBodySize(Body body)
{
float maxTop = 0, maxRight = 0, maxBottom = 0, maxLeft = 0;
for(Fixture f : body.getFixtureList())
{
MyVector4 vec = outerVals(f);
if(vec.a > maxTop)
maxTop = vec.a;
if(vec.b > maxRight)
maxRight = vec.b;
if(vec.c > maxBottom)
maxBottom = vec.c;
if(vec.d > maxLeft)
maxLeft = vec.d;
}
return new Vector2(Math.abs(maxRight - maxLeft), Math.abs(maxTop - maxBottom));
}
public static Vector2 getBodySize(Body body, float scale)
{
float maxTop = 0, maxRight = 0, maxBottom = 0, maxLeft = 0;
for(Fixture f : body.getFixtureList())
{
MyVector4 vec = outerVals(f).scale(scale);
if(vec.a > maxTop)
maxTop = vec.a;
if(vec.b > maxRight)
maxRight = vec.b;
if(vec.c > maxBottom)
maxBottom = vec.c;
if(vec.d > maxLeft)
maxLeft = vec.d;
}
return new Vector2(Math.abs(maxRight - maxLeft), Math.abs(maxTop - maxBottom));
}
/**
* Changing which method is called based on the fixture's shape
* @param fixture the current fixture being analyzed
* @return the outermost points of the fixture's shape
*/
private static MyVector4 outerVals(Fixture fixture)
{
Shape shape = fixture.getShape();
Shape.Type type = shape.getType();
MyVector4 size = new MyVector4();
switch(type)
{
case Polygon:
size = shapeVals((PolygonShape)shape);
break;
case Chain:
size = shapeVals((ChainShape)shape);
break;
case Edge:
size = shapeVals((EdgeShape)shape);
break;
case Circle:
size = shapeVals((CircleShape)shape);
break;
}
return size;
}
/**
* Calculates the outermost points for a PolygonShape
* @param s the shape
* @return the maximum upper, lower, left, and right values; given by the vertices
*/
private static MyVector4 shapeVals(PolygonShape s)
{
MyVector4 size = new MyVector4(); // top, right, bottom, left
for(int i = 0; i < s.getVertexCount(); i++)
{
Vector2 probe = new Vector2();
s.getVertex(i, probe);
if(probe.x > size.b) // right
size.b = probe.x;
if(probe.x < size.d) // left
size.d = probe.x;
if(probe.y > size.a) // top
size.a = probe.y;
if(probe.y < size.c) // bottom
size.c = probe.y;
}
return size;
}
/**
* Calculates the outermost points for a ChainShape
* @param s the shape
* @return the maximum upper, lower, left, and right values; given by the vertices
*/
private static MyVector4 shapeVals(ChainShape s)
{
MyVector4 size = new MyVector4(); // top, right, bottom, left
for(int i = 0; i < s.getVertexCount(); i++)
{
Vector2 probe = new Vector2();
s.getVertex(i, probe);
if(probe.x > size.b) // right
size.b = probe.x;
if(probe.x < size.d) // left
size.d = probe.x;
if(probe.y > size.a) // top
size.a = probe.y;
if(probe.y < size.c) // bottom
size.c = probe.y;
}
return size;
}
/**
* Calculates the outermost points for an EdgeShape
* @param s the shape
* @return the maximum upper, lower, left, and right values; given by the vertices
*/
private static MyVector4 shapeVals(EdgeShape s)
{
MyVector4 size = new MyVector4(); // top, right, bottom, left
Vector2 probe = new Vector2();
s.getVertex1(probe);
if(probe.x > size.b) // right
size.b = probe.x;
if(probe.x < size.d) // left
size.d = probe.x;
if(probe.y > size.a) // top
size.a = probe.y;
if(probe.y < size.c) // bottom
size.c = probe.y;
s.getVertex2(probe);
if(probe.x > size.b) // right
size.b = probe.x;
if(probe.x < size.d) // left
size.d = probe.x;
if(probe.y > size.a) // top
size.a = probe.y;
if(probe.y < size.c) // bottom
size.c = probe.y;
return size;
}
/**
* Calculates the outermost points for a CircleShape
* @param s the shape
* @return the maximum upper, lower, left, and right values; given by radius and position
*/
private static MyVector4 shapeVals(CircleShape s)
{
MyVector4 size = new MyVector4(); // top, right, bottom, left
size.a = s.getPosition().y + s.getRadius(); // top
size.b = s.getPosition().x + s.getRadius(); // right
size.c = s.getPosition().y - s.getRadius(); // bottom
size.d = s.getPosition().x - s.getRadius(); // left
return size;
}
/**
* using this just to store the variables easily
*/
private static class MyVector4
{
public float a, b, c, d;
public MyVector4()
{
this.a = 0;
this.b = 0;
this.c = 0;
this.d = 0;
}
@SuppressWarnings("unused")
public MyVector4(float a, float b, float c, float d)
{
this.a = a;
this.b = b;
this.c = c;
this.d = d;
}
@SuppressWarnings("unused")
public void set(float a, float b, float c, float d)
{
this.a = a;
this.b = b;
this.c = c;
this.d = d;
}
public MyVector4 scale(float val)
{
this.a *= val;
this.b *= val;
this.c *= val;
this.d *= val;
return this;
}
}
}
【讨论】：
我以前遇到过这个问题，这是对我有用的解决方案，您必须遍历所有灯具，然后开始获取每个灯具的 b2AABB 矩形并将它们组合在一起，然后获得组合 AABB 的宽度和高度
b2AABB aabb;
b2Transform t;
t.SetIdentity();
b2Fixture* fixture = nearBody->GetFixtureList();
while (fixture != NULL) {
const b2Shape *shape = fixture->GetShape();
const int childCount = shape->GetChildCount();
for (int child = 0; child < childCount; ++child) {
b2AABB shapeAABB;
shape->ComputeAABB(&shapeAABB, t, child);
shapeAABB.lowerBound = shapeAABB.lowerBound;
shapeAABB.upperBound = shapeAABB.upperBound;
aabb.Combine(shapeAABB);
}
fixture = fixture->GetNext();
}
CCPoint lowerVertex = aabb.lowerBound;
CCPoint heigherVertex = aabb.upperBound;
bodyWidth = heigherVertex.x - lowerVertex.x;
bodyHeight = heigherVertex.y - lowerVertex.y;
【讨论】：
检查 b2World.cpp，有一些代码可以帮助你：
void b2World::DrawDebugData() {
...
for (b2Body* b = m_bodyList; b; b = b->GetNext()) {
const b2Transform& xf = b->GetTransform();
for (b2Fixture* f = b->GetFixtureList(); f; f = f->GetNext()) {
...
DrawShape(f, xf, b2Color(0.5f, 0.5f, 0.3f));
}
}
...
}
void b2World::DrawShape(b2Fixture* fixture, const b2Transform& xf, const b2Color& color) {
...
case b2Shape::e_polygon: {
b2PolygonShape* poly = (b2PolygonShape*)fixture->GetShape();
int32 vertexCount = poly->m_count;
b2Vec2 vertices[b2_maxPolygonVertices];
for (int32 i = 0; i < vertexCount; ++i) {
//they are polygen's vertices, you can use these to get the height / width
vertices[i] = b2Mul(xf, poly->m_vertices[i]);
}
m_debugDraw->DrawSolidPolygon(vertices, vertexCount, color);
}
...
}
【讨论】：
这是我在学习this libgdx 教程时想到的。
float w2 = 0f
float h2 = 0f
b.body.fixtureList.each { Fixture fixture ->
if(fixture) {
if(fixture.shape.type == Shape.Type.Circle) {
w2 += fixture.shape.radius * 2
h2 += fixture.shape.radius * 2
} else if(fixture.shape.type == Shape.Type.Polygon) {
PolygonShape shape = fixture.shape as PolygonShape
Vector2 vector = new Vector2()
def vectors = []
shape.vertexCount.times {
shape.getVertex(it, vector)
vectors.add(new Vector2(vector.x, vector.y))
}
vectors.sort {it.x}
w2 = (vectors.first().x).abs() + (vectors.last().x).abs()
vectors.sort {it.y}
h2 = (vectors.first().y).abs() + (vectors.last().y).abs()
}
}
}
【讨论】：
嗯，我不太确定，但这似乎很复杂，因为一个 box2d 主体可以由多个 Fixtures 组成，每个 Fixtures 都有不同的形状。
您只是在寻找边界框的宽度和高度吗？
然后您可能必须遍历身体的夹具列表并评估其中的形状，查看形状的位置并计算边界框。不幸的是，这看起来不太舒服。
【讨论】：
((Sprite)body.getUserData()).getWidth();
((Sprite)body.getUserData()).getHeight();
使用它.. 如果我猜对了，它应该会回答您的问题
【讨论】：
如果您只是将多边形形状用作盒子，为什么不创建一个包装类。并将宽度、高度和位置等相关信息存储在包装类变量中。
【讨论】：
（如果您在运行时更改主体大小（添加/删除固定装置），则在将主体大小更改为以下方法时可能需要进行一些修改，但它应该可以工作。）
注意：我使用的是Java+jbox2d
我能想到的最简单的方法是自己在对象中存储高度和宽度，就像在创建主体时一样
float objectHeight;
float objectWidth;
当您创建身体（特别是形状）时。 只需将所有维度加在一起
objectWidth = fixture1Shape.width + ...;
objectHeight = fixture1Shape.height + ...;
那么它只是在对象中制作自定义方法
float getWidth(){
return objectWidth;
}
float getHeight(){
return objectHeight;
}
现在您可以获得对象主体的确切宽度和高度。 使用
o1.getHeight();
o1.getWidth();
[考虑到 o1 是您找到对象的位置，例如 Object o1 = fixture.getUserData(); 或 Object o1=body.getUserData()]
您可能需要创建所需类的新对象并将其转换为对象，然后再调用方法
//consider your object class is Player
Player p1 = (Player) o1;
p1.getHeight();
p1.getWidth();
PS：如果您需要 Box2D 世界大小，只需使用您的缩放因子对其进行缩放。 或者更好的是在创建形状时将其作为缩放版本存储在 objectHeight,objectWidth 中
【讨论】：