我必须编写一个函数，它检测交集并返回true或false。
我有Shape.cpp文件，而rectangle.cpp，circle.cpp文件继承了它。我试着计算它，但我失败了。没有错误，但是当我的程序启动时，它会崩溃。我的问题是它崩溃的原因？我的方式是错的吗？这是circle.cpp文件。
bool Circ::intersects(Shape* pshape)
{
Rect *p1 = dynamic_cast<Rect*>(pshape);
Circ *p2 = dynamic_cast<Circ*>(pshape);
if(p1)
{
float circleDistance_x = abs(p2->getPos().x - p1->getPos().x);
float circleDistance_y = abs(p2->getPos().y - p1->getPos().y);
if(circleDistance_x > (p1->getSize().x/2 + p2->getRad()))
return false;
if(circleDistance_y > (p1->getSize().y/2 + p2->getRad()))
return false;
if(circleDistance_x <= (p1->getSize().x/2))
return true;
if(circleDistance_y <= (p1->getSize().y/2))
return true;
float cornerDistance_sq = (circleDistance_x - (p1->getSize().x/2)) + (circleDistance_y - (p1->getSize().y/2))*(circleDistance_y - (p1->getSize().y/2));
return (cornerDistance_sq <= p2->getRad()^2);
}
return false;
}
这不是我想写的代码。但是当它失败时，我就停下来写了。
和我的Shapes.h文件
#ifndef _SHAPES_H
#define _SHAPES_H
struct Point2d
{
float x, y;
};
struct Point3d
{
float r, g, b;
};
class Shape
{
protected:
bool m_bMarked;
Point3d m_col;
Point2d m_veldir;
Point2d m_pos;
float m_vel;
public:
Shape(Point2d& pos, Point2d& veldir, float vel, Point3d& col)
:m_pos(pos),m_veldir(veldir),m_vel(vel),m_col(col)
{
m_bMarked = false;
}
virtual ~Shape() {}
virtual void draw() = 0;
virtual bool intersects(Shape*) = 0;
inline void move() { m_pos.x += m_veldir.x*m_vel; m_pos.y += m_veldir.y*m_vel; }
inline void invert_xdir() { m_veldir.x *= -1; }
inline void invert_ydir() { m_veldir.y *= -1; }
inline void MarkShape() { m_bMarked = true; }
inline void UnMarkShape() { m_bMarked = false; }
inline bool isMarked() { return m_bMarked; }
inline void increase_vel() { m_vel += 0.01f; }
inline void decrease_vel() { m_vel -= 0.01f; }
};
#endif
最后是我的ShapesMain.cpp文件
#include <time.h>
#include <GL/glut.h>
#include <cmath>
#include "Rectangle.h"
#include "Circle.h"
// YOU CAN CHANGE THE NUMBER OF SHAPES
#define SHAPE_COUNT 20
// YOU CAN MODIFY WINDOW SIZE BY CHANGING THESE
// YOU MAY ALSO VIEW WINDOW IN FULL SCREEN
#define WINDOWX 500
#define WINDOWY 500
// UNCOMMENT THE LINE BELOW TO STOP MOVING SHAPES
//#define NO_MOTION
// CHANGE THESE DIMENSIONS HOWEVER YOU LIKE
#define MAX_SHAPE_DIM 70
#define MIN_SHAPE_DIM 10
float g_windowWidth = WINDOWX;
float g_windowHeight = WINDOWY;
Shape* g_shapeList[SHAPE_COUNT];
int g_numShapes = 0;
bool g_bShowIntersection = true;
//------------------------------------
void Initialize()
{
srand ( time(NULL) );
// delete previous shapes, if there is any
if (g_numShapes > 0)
{
for (int i = 0; i < g_numShapes; i++)
delete g_shapeList[i];
}
// create a new shape repository
do {
g_numShapes = rand() % SHAPE_COUNT; // number of shapes are randomly determined
} while (g_numShapes < 5); // we dont want to have less than 5 shapes
int rect_count = g_numShapes * (rand() % 10 / 10.0f);
int circle_count = g_numShapes - rect_count;
int half_wind_x = 3* g_windowWidth / 4;
int half_wind_y = 3* g_windowHeight / 4;
int max_dim = MAX_SHAPE_DIM; // max dim. of any shape
int min_dim = MIN_SHAPE_DIM; // min dim. of any shape
int quad_wind = g_windowWidth / 4;
for (int i= 0; i<g_numShapes; i++)
{
float x, y;
float v1, v2;
// set positions
do {
x = rand() % half_wind_x;
} while (x <= quad_wind);
do {
y = rand() % half_wind_y;
} while (y <= quad_wind);
Point2d pos = { x,y };
// set velocity directions
do{
v1 = rand() % 10 / 10.0f;
v2 = rand() % 10 / 10.0f;
} while (v1 == 0 || v2 == 0);
v1 *= (rand() % 2) ? -1 : 1;
v2 *= (rand() % 2) ? -1 : 1;
float vnorm = sqrt(v1*v1 + v2*v2);
Point2d veldir = { v1 / vnorm, v2 / vnorm };
// set velocity
float vel;
do {
vel = rand() % 2 / 10.0f;
} while (vel == 0);
#ifdef NO_MOTION
vel = 0.0f;
#endif
//set color
float R = rand()%100/100.0f;
float G = rand()%100/100.0f;
float B = rand()%100/100.0f;
Point3d color = { R,G,B };
// construct objects
if (i < rect_count)
{
float wx;
float wy;
do {
wx = rand() % quad_wind;
} while (wx < min_dim || wx>max_dim);
do {
wy = rand() % quad_wind;
} while (wy < min_dim || wy>max_dim);
Point2d size = { wx, wy };
Rect* pRect = new Rect(pos, size, veldir, vel, color);
g_shapeList[i] = pRect;
}
else
{
float rad;
do {
rad = rand() % quad_wind;
} while (rad < min_dim || rad>max_dim);
Circ* pCirc = new Circ(pos, rad, veldir, vel, color);
g_shapeList[i] = pCirc;
}
}
glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
}
//-------------------------------------
// This function handles the intersections of shapes.
// if the user is not interested in marking intersections
// s/he can set bMarkIntersections to false..in this case
// no intersection test is performed
void MarkObjects(bool bMarkIntersections)
{
if (bMarkIntersections == false)
{
for (int i = 0; i < g_numShapes; i++)
g_shapeList[i]->UnMarkShape();
}
else
{
// reset the states of all shapes as unmarked
for (int i = 0; i < g_numShapes; i++)
g_shapeList[i]->UnMarkShape();
for (int i = 0; i < g_numShapes; i++)
{
for (int j = i+1; j < g_numShapes; j++)
{
if (g_shapeList[i]->intersects(g_shapeList[j]))
{
g_shapeList[i]->MarkShape();
g_shapeList[j]->MarkShape();
}
}
}
}
}
//------------------------------------
void UpdateData()
{
// create viewport bounding rectangles to keep the shapes within the viewport
Point2d Winpos = { -1.0,0.0 };
Point2d Winsize = { 1.0 , g_windowHeight };
Point2d Winveldir = { 0,0 }; // dummy veldir
float Winvel = 0.0f; //not moving
Point3d Wincol = { 0,0,0 }; // dummy color
Rect WindowRectLeft(Winpos, Winsize, Winveldir, Winvel, Wincol);
Winpos.x = 0.0; Winpos.y = -1.0;
Winsize.x = g_windowWidth; Winsize.y = 1.0;
Rect WindowRectBottom(Winpos, Winsize, Winveldir, Winvel, Wincol);
Winpos.x = g_windowWidth; Winpos.y = 0.0;
Winsize.x = 1; Winsize.y = g_windowHeight;
Rect WindowRectRight(Winpos, Winsize, Winveldir, Winvel, Wincol);
Winpos.x = 0.0; Winpos.y = g_windowHeight;
Winsize.x = g_windowWidth; Winsize.y = 1.0f;
Rect WindowRectUp(Winpos, Winsize, Winveldir, Winvel, Wincol);
for (int i = 0; i < g_numShapes; i++)
{
// move the shape
g_shapeList[i]->move();
// if it bounces to the window walls, invert its veldir
if (g_shapeList[i]->intersects(&WindowRectLeft) ||
g_shapeList[i]->intersects(&WindowRectRight))
g_shapeList[i]->invert_xdir();
if (g_shapeList[i]->intersects(&WindowRectBottom) ||
g_shapeList[i]->intersects(&WindowRectUp))
g_shapeList[i]->invert_ydir();
}
}
//------------------------------------
void ChangeSize(GLsizei w, GLsizei h)
{
if(h == 0)
h = 1;
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
g_windowHeight = h;
g_windowWidth = w;
glOrtho(0, g_windowWidth, 0, g_windowHeight , 1.0f, -1.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
//------------------------------------
void processNormalKeys(unsigned char key, int x, int y)
{
if (key == 'q') // PRESS 'q' to terminate the application
exit(0);
if(key=='r') // PRESS 'r' ket to reset the shapes
Initialize();
if (key == 's') // toggle between showing the intersections or not
g_bShowIntersection = g_bShowIntersection ? false: true;
}
//------------------------------------
void processSpecialKeys(int key, int x, int y)
{
switch(key) {
case GLUT_KEY_LEFT :
break;
case GLUT_KEY_RIGHT :
break;
case GLUT_KEY_UP:
// PRESSING UP ARROW KEY INCREASES THE SHAPE VELOCITIES
for (int i = 0; i < g_numShapes; i++)
g_shapeList[i]->increase_vel();
break;
case GLUT_KEY_DOWN:
// PRESSING DOWN ARROW KEY DECREASES THE SHAPE VELOCITIES
for (int i = 0; i < g_numShapes; i++)
g_shapeList[i]->decrease_vel();
break;
}
}
//-------------------------------------
void display() {
glClear(GL_COLOR_BUFFER_BIT); // Clear the color buffer
glEnable(GL_BLEND); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
UpdateData();
MarkObjects(g_bShowIntersection);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
for (int i= 0; i<g_numShapes; i++)
g_shapeList[i]->draw();
glutSwapBuffers();
}
//------------------------------------
int main(int argc, char* argv[])
{
glutInit(&argc, argv); // Initialize GLUT
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB );
glutInitWindowPosition(100,100);
glutInitWindowSize(WINDOWX, WINDOWY);
glutCreateWindow("COM102B - PA4");
// Register callback handler for window re-paint
glutDisplayFunc(display);
glutReshapeFunc(ChangeSize);
glutIdleFunc(display);
glutKeyboardFunc(processNormalKeys);
glutSpecialFunc(processSpecialKeys);
Initialize();
glutMainLoop(); // Enter infinitely event-processing loop
return 0;
}
答案 0 :(得分：0)
你的问题在于以下几点：
Rect *p1 = dynamic_cast<Rect*>(pshape);
Circ *p2 = dynamic_cast<Circ*>(pshape);
除非你从Circ继承了Rect，反之亦然，这是导致程序崩溃的原因，如果它是一个Rect，你就不能将你的pShape转换为Circ，所以当你将一个Rect对象传递给你的函数时，它将会正确转换为Rect *但它将失败并且Circ *返回nullptr，所以当你尝试从p2访问方法时它会崩溃因为你正在访问无效内存（0x00000000）：
if(p1)
{
float circleDistance_x = abs(p2->getPos().x - p1->getPos().x);
float circleDistance_y = abs(p2->getPos().y - p1->getPos().y);
if(circleDistance_x > (p1->getSize().x/2 + p2->getRad()))
return false;
if(circleDistance_y > (p1->getSize().y/2 + p2->getRad()))
return false;
if(circleDistance_x <= (p1->getSize().x/2))
return true;
if(circleDistance_y <= (p1->getSize().y/2))
return true;
float cornerDistance_sq = (circleDistance_x - (p1->getSize().x/2)) + (circleDistance_y - (p1->getSize().y/2))*(circleDistance_y - (p1->getSize().y/2));
return (cornerDistance_sq <= p2->getRad()^2);
}
所以，你可以简单地抛出第一个p1指针，因为该方法来自圆圈，很明显它是从Circ对象调用的，所以不需要p2指针。
Rect *p1 = dynamic_cast<Rect*>(pshape);
if(p1)
{
float circleDistance_x = abs(getPos().x - p1->getPos().x);
float circleDistance_y = abs(getPos().y - p1->getPos().y);
if(circleDistance_x > (p1->getSize().x/2 + getRad()))
return false;
if(circleDistance_y > (p1->getSize().y/2 + getRad()))
return false;
if(circleDistance_x <= (p1->getSize().x/2))
return true;
if(circleDistance_y <= (p1->getSize().y/2))
return true;
float cornerDistance_sq = (circleDistance_x - (p1->getSize().x/2)) + (circleDistance_y - (p1->getSize().y/2))*(circleDistance_y - (p1->getSize().y/2));
return (cornerDistance_sq <= getRad()^2);
}
同样在线：
return (cornerDistance_sq <= getRad()^2)
我认为你正试图获得半径方形，但这不会做，它实际上在做什么
(cornerDistance_sq <= getRad()) ^ 2
becouse＆lt; =具有更高的^优先级，加上^不是方运算符，它是一个按位运算符。所以你真正想要的是：
return cornerDistance_sq <= getRad() * getRad();