Question

我试图创建一个Box2D程序，但我需要启用debugdraw来查看正在进行的操作。我正在考虑使用Box2D库中包含的Helloworld程序作为模板。不幸的是，它没有使用debugdraw，我似乎无法实现它。 Testbed使用它，但它有点复杂，解释得太差，无法用作模板。那么这里的任何人都可以使用debugdraw分享Helloworld.cpp（或使用Box2D的类似基本程序）的示例（最好像在Testbed中一样实现）吗？

我使用VS2013，如果重要的话。

谢谢和问候。

Answer 1

如果您还没有想到这一点（以及未来的观众），核心Box2D库没有可以简单地“启用”的调试绘图功能。它是一个物理引擎，而不是渲染引擎。

那就是说，你不必从头开始做所有事情。 Testbed有一个调试绘图的实现，你可以在那里运行make a test。 Box2D还提供了一种绘图模板，以防您想要实现自己的渲染代码。从本质上讲，有一些回调可以放置代码，例如，多边形渲染。对于每个多边形，Box2D的每个帧都将调用该回调，并且您的多边形将在屏幕上呈现！

你问了一个简单的例子，所以这里有一个使用GLFW进行窗口化和裸露的OpenGL来进行渲染。这里有很多教程，但你并不需要了解它们以了解代码。

Main.cpp的：

#define GLEW_STATIC
#include <GLFW\glfw3.h>
#include <Box2D\Box2D.h>
#include "Physics.h"

int main() {
    // Initialize window (this is GLFW-specific)
    GLFWwindow* window;
    if (!glfwInit()) return 1;
    window = glfwCreateWindow(960, 540, "Box2D Debug Draw", NULL, NULL);
    if (!window) {
        glfwTerminate();
        return 2;
    }
    glfwMakeContextCurrent(window);
    glfwSwapInterval(1);

    DebugDraw debugDraw; // Declare an instance of our DebugDraw class so we can actually use it

    // Set up Box2D world, bodies, etc. (you should be familiar with most of this)
    int velocityIterations = 8;
    int positionIterations = 3;
    b2World* world;
    b2Body* groundBody;
    b2Body* testBody;
    {
        b2Vec2 gravity(0.0f, -10.0f);
        world = new b2World(gravity);
        world->SetDebugDraw(&debugDraw); // YOU NEED THIS SO BOX2D KNOWS WHERE TO LOOK FOR DRAWING CALLBACKS
        debugDraw.SetFlags(b2Draw::e_shapeBit);
    }
    {
        b2BodyDef gbDef;
        gbDef.position.Set(0.0f, -10.0f);
        groundBody = world->CreateBody(&gbDef);

        b2PolygonShape gbShape;
        gbShape.SetAsBox(50.0f, 10.0f);

        groundBody->CreateFixture(&gbShape, 0.0f);
    }
    {
        b2BodyDef tbDef;
        tbDef.type = b2_dynamicBody;
        tbDef.position.Set(0.0f, 10.0f);
        testBody = world->CreateBody(&tbDef);

        b2PolygonShape tbShape;
        tbShape.SetAsBox(1.0f, 1.0f);

        b2FixtureDef tbFix;
        tbFix.shape = &tbShape;
        tbFix.density = 1.0f;
        tbFix.friction = 0.3f;

        testBody->CreateFixture(&tbFix);
    }

    // Loop until user exits
    b2Timer timer;
    float last = timer.GetMilliseconds();
    while (!glfwWindowShouldClose(window)) {
        float now = timer.GetMilliseconds();
        world->Step((now - last) / 1000, 8, 3); // Step simulation forward by amount of time since last step
        last = now;

        glClear(GL_COLOR_BUFFER_BIT); // Clear screen
        glPushMatrix(); // Push matrix so we can revert after doing some transformations
        glScalef(40.0f / 960.0f, 40.0f / 540.0f, 1.0f); // Zoom out
        glTranslatef(0.0f, -5.0f, 0.0f); // Pan up
        world->DrawDebugData(); // CALL THE DRAWING CALLBACKS WE SET UP IN PHYSICS CLASS
        glPopMatrix(); // Revert transformations

        glfwSwapBuffers(window); // Push updated buffers to window
        glfwPollEvents(); // Poll user events so OS doesn't think app is frozen
    }

    // Garbage collection
    delete world;
    glfwDestroyWindow(window);
    glfwTerminate();
    return 0;
}

Physics.h：

#ifndef PHYSICS
#define PHYSICS

#include <Box2D\Box2D.h>

class DebugDraw : public b2Draw { // b2Draw has all the virtual functions that we need to override here
public:
    // We won't be implementing all of these, but if we don't declare them here we'll get an override error
    void DrawSolidPolygon(const b2Vec2* vertices, int32 vertexCount, const b2Color& color);
    void DrawPolygon(const b2Vec2* vertices, int32 vertexCount, const b2Color& color);
    void DrawCircle(const b2Vec2& center, float32 radius, const b2Color& color);
    void DrawSolidCircle(const b2Vec2& center, float32 radius, const b2Vec2& axis, const b2Color& color);
    void DrawSegment(const b2Vec2& p1, const b2Vec2& p2, const b2Color& color);
    void DrawTransform(const b2Transform& xf);
};

#endif

Physics.cpp：

#include <GL\glew.h>
#include "Physics.h"

void DebugDraw::DrawSolidPolygon(const b2Vec2* vertices, int32 vertexCount, const b2Color& color) {
    // Standard OpenGL rendering stuff
    glColor4f(color.r, color.g, color.b, color.a);
    glBegin(GL_POLYGON); 
    for (int i = 0; i < vertexCount; i++) {
        glVertex2f(vertices[i].x, vertices[i].y);
    }
    glEnd();
}

// We just need to have these to prevent override errors, they don't actually do anything right now
void DebugDraw::DrawPolygon(const b2Vec2* vertices, int32 vertexCount, const b2Color& color) {}
void DebugDraw::DrawCircle(const b2Vec2& center, float32 radius, const b2Color& color) {}
void DebugDraw::DrawSolidCircle(const b2Vec2& center, float32 radius, const b2Vec2& axis, const b2Color& color) {}
void DebugDraw::DrawSegment(const b2Vec2& p1, const b2Vec2& p2, const b2Color& color) {}
void DebugDraw::DrawTransform(const b2Transform& xf) {}

Box2D：在Helloworld.cpp或类似的基本程序中使用debugdraw？

1 个答案: