c++ - opengl中的有界框碰撞检测

Question

这是程序的覆盖图。我在 Visual Studio 10 中工作，使用 opengl/glut 的 c++。我正在尝试创建一个迷宫（我从输入文件生成）。然后我使用 obj loader(glm) 从 3dstudio max 导入两个模型。其中一个模型（mo）将在迷宫中移动。所以我在他周围和迷宫的墙壁周围添加了一个边界框。我还在 mo 周围画了一个盒子，它似乎随着角色移动/旋转。但是由于某种原因（也许我没有在正确的地方做）碰撞测试从来没有检测到任何东西。我会让代码来说话，如果您有任何问题，我很乐意解决它们。现在准备代码。

//bounding boxes
struct BoundingBox
{
    Vector3D max;
    Vector3D min;
};
BoundingBox *box_mo;
BoundingBox *static_box[400];

void initbox(BoundingBox *b){
    b->min.x=100000;
    b->min.y=100000;
    b->min.z=100000;
    b->max.x=-100000;
    b->max.y=-100000;
    b->max.z=-100000;
}

BoundingBox *CreateCollisionBox(GLMmodel *model,GLMgroup *object){
/* GLM doesn't store each vertex together with the object that owns it. It doesn't have that notion. In GLM object don't have vertex, they have triangles. And each triangle is actually an index in the triangle list of the object.*/
    BoundingBox *boxx=(BoundingBox*)malloc(sizeof(BoundingBox));
    initbox(boxx);
    for(int i=0;i<object->numtriangles;i++){
// for each vertex of the triangle pmodel1->triangles[object->triangles[i]]
// calculate min and max
        for(int j=0;j<3;j++){
            GLuint index=model->triangles[object->triangles[i]].vindices[j];
            GLfloat x = model->vertices[index*3 +0];
            GLfloat y = model->vertices[index*3 +1];
            GLfloat z = model->vertices[index*3 +2];
            if(boxx->min.x>x) boxx->min.x =x;
            if(boxx->min.y>y) boxx->min.y =y;
            if(boxx->min.z>z) boxx->min.z =z;

            if(boxx->max.x<x) boxx->max.x =x;
            if(boxx->max.y<y) boxx->max.y =y;
            if(boxx->max.z<z) boxx->max.z =z;
        }
    }
    return boxx;
}

void AddCollisionBox(GLMmodel *model,GLMgroup *object){
    //box[boxindex]=CreateCollisionBox(model,object);
    box_mo=CreateCollisionBox(model,object);
    //boxindex++;
}
// A GLMmodel has a chained list of groups, each group representing an object. 
// Each object has a name (the name you gave it in 3D Studio Max or Gmax).
// Let's you have 10 walls in your scene a few other objects as well and you want to 
// create collision boxes just for the walls and you do not want to make a collision box 
// for one of your objects. You could name all your walls
// like this: Wall1, Wall2, ..., Wall10. If you wanted to add collision boxes just to them 
// you could go through all objects in the scene and if their name contains "Wall" add them.
// with this one: strstr
// Basicly this function does just that: if you want to add boxes for the walls you would call it like this: DefineCollisionBoxes(model,"Wall"); 
void DefineCollisionBoxes(GLMmodel *model,char *name){
    GLMgroup *group = model->groups;
    while(group){
        if(strstr(group->name,name))
            AddCollisionBox(model,group);
        group=group->next;
    }
}

bool Collision(BoundingBox *b,GLfloat x,GLfloat y,GLfloat z){
    return x <= b->max.x && x>= b->min.x && y<= b->max.y && y>= b->min.y && z<= b->max.z && z >= b->min.z;
}

bool CollisionTest(BoundingBox *a,BoundingBox *b){
    /*bool collision=false;
    for(int i=0;i<static_boxes;i++){
        for(float x=static_box[i]->min.x, y=static_box[i]->min.y,z=static_box[i]->min.z ;x<=static_box[i]->max.x && y<=static_box[i]->max.y && z<=static_box[i]->max.z;x+=0.1,y+=0.1,z+=0.1){
            if(Collision(a,x,y,z) == true)
                collision=true;
        }
    }
    return collision;*/
    if(a->min.x <= b->max.x && a->max.x >= b->min.x && a->min.z <= b->max.z && a->max.z >= b->min.z && a->min.y <= b->max.y && a->max.y >= b->min.y)
        return true;
    return false;
}

void drawBox(BoundingBox *b){
    glColor3f(1,1,1);
    glBegin(GL_LINE_LOOP);
    glVertex3f(b->max.x,b->max.y,b->min.z);
    glVertex3f(b->min.x,b->max.y,b->min.z);
    glVertex3f(b->min.x,b->min.y,b->min.z);
    glVertex3f(b->max.x,b->min.y,b->min.z);
    glEnd();

    glBegin(GL_LINE_LOOP);
    glVertex3f(b->max.x,b->min.y,b->max.z);
    glVertex3f(b->max.x,b->max.y,b->max.z);
    glVertex3f(b->min.x,b->max.y,b->max.z);
    glVertex3f(b->min.x,b->min.y,b->max.z);
    glEnd();

    glBegin(GL_LINE_LOOP);
    glVertex3f(b->max.x,b->max.y,b->min.z);
    glVertex3f(b->max.x,b->max.y,b->max.z);
    glVertex3f(b->min.x,b->max.y,b->max.z);
    glVertex3f(b->min.x,b->max.y,b->min.z);
    glEnd();

    glBegin(GL_LINE_LOOP);
    glVertex3f(b->max.x,b->min.y,b->max.z);
    glVertex3f(b->min.x,b->min.y,b->max.z);
    glVertex3f(b->min.x,b->min.y,b->min.z);
    glVertex3f(b->max.x,b->min.y,b->min.z);
    glEnd();
}


//display function
void display(){
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    //setup view
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    camera.render
    //read from file, create walls and characters 
    //place model mo in front of the third person camera always
    Vector3D positionn;
    positionn = camera.position + camera.forward*5;

    glPushMatrix();
    glColor3f(0.88f,0.75f,0.49f);
    //here i move my character and calculate bounding box at each frame for him
    glTranslatef(positionn.x,-0.42f,positionn.z);
    glScalef(0.7f,0.7f,0.7f);
    glRotatef(angle,0,1,0);
    drawMo();
    DefineCollisionBoxes(pmodel1,"body"); // actual function call
    drawBox(box_mo); //draw bounding box
    glPopMatrix();

    //test if the character collides with any of the walls - not working
    for(int i=0;i<static_boxes;i++){
        if(CollisionTest(box_mo,static_box[i]) == true){
            printf("collision");
        }
    }


    //swap buffers
    glutSwapBuffers();
}

Answer 1

我将尝试概述如何解决碰撞问题。为简单起见，我将做出以下假设：

1. 我们有一个迷宫所在的坐标系。
2. 相机和模型都转换到这个坐标系中。
3. 为了使墙壁到达该坐标系，对墙壁执行的唯一转换是纯平移，无需任何旋转或缩放。
4. 字符将被平移、旋转和缩放。
5. 您不想检查是否会发生碰撞，而是要检查是否发生了碰撞。
6. 您拥有或将编写或获取向量和矩阵库

如果我们使用这些假设，我们可以使用 3d 中的矩形来表示每面墙。而且由于我们假设迷宫既不旋转也不缩放，我们可以只做一次，然后将其存储在数组或 B-tree 或其他任何东西中。（请注意，选择正确的数据结构来存储您的世界进行计算可以大大提高性能）

角色在迷宫中移动，我们假设它可以旋转和缩放。确定角色是否与任何物体发生碰撞的最简单方法是计算对象的边界球。一旦你有了碰撞检测，你可以只存储两点。球体的中心点和球体上的任意点。

一旦角色被带到迷宫中的正确位置，您就可以对提到的两个点应用完全相同的变换。您可以使用矩阵库执行此操作，也可以在转换字符后查询 MODELVIEW 矩阵。您可以像这样调用“glGetFloatv”来做到这一点：

GLfloat model[16]; 
glGetFloatv(GL_MODELVIEW_MATRIX, model); 

一旦你变换了这两个点，你就可以找到它们之间的距离——这将是一个物体必须远离变换后的中心点以避免碰撞的距离。

现在要做的最后一件事是检查相关平面并使用转换后的中心点和计算的距离检查点到平面的距离。然后，您需要确保投影到平面的中心落在矩形内。

这是程序的概要（这里没有真正的代码，只有注释和函数抽象）

void drawCharacter(Matrix4f const & charMatrix);
void drawMaze(Matrix4f const & mazeMatrix);
//Will return MAX_FLT to indicate out of rectangle condition
float distanceToRectangle(Vector3f const & point, Rectangle3df const & plane);
vector<Rectangle3df> wallPlanes;
Vector3f centerOfCharSphere;
Vector3f pointOnCharSphere;
//Initialization
/*
1. Go Over maze create planes for all walls
2. Calculate character sphere and extract two points: The center of the sphere and a point on the sphere
*/

//Render
/*
Calculate the charMatrix - The matrix that takes the character from object CRS to maze CRS
Calculate the translation matrix for the maze (mazeMatrix) - the matrix that translates the maze into place
*/

Vector3f transformedSphereCenter = charMatrix.transform(centerOfCharSphere);
Vector3f transformedPointOnSphere = charMatrix.transform(pointOnCharSphere);
Vector3f R = transformedPointOnSphere - transformedSphereCenter;
float safeDistance = R.length();
for(vector<Plane3f>::const_iterator it = wallPlanes.begin(); it != wallPlanes.end(); it++)
{
    if(distanceToRectangle(transformedSphereCenter, *it) <= safeDistance)
       printf("collided\n");
}

/*
Setup projection matrix
Setup the modelview matrix for the camera
*/
drawMaze(mazeMatrix);
drawCharacter(charMatrix);

我希望这能让你走上正轨