OpenGL de プログラミング

平面 x + y + z = 5 と 2点(0,0,0),(5,3,5)をむすんだ線分の交点pを求めよ。

参考
http://www.hiramine.com/programming/graphics/index...

#include <cstdio>
#include <GL/glut.h>
#include <GL/glu.h>
#include <GL/gl.h>

struct point3d
{
double x;
double y;
double z;
};
typedef struct point3d POINT_3D;



void display();
void reshape(int w, int h);

inline void DRAW_XYZ();
inline void DRAW_PLANE();
inline void CALC_CROSS_POINT3D();
inline void DRAW_CROSS_POINT3D();
inline void DRAW_LINES();

using namespace std;


inline void GLUT_INIT()
{
glutInitDisplayMode(GLUT_RGBA| GLUT_DOUBLE | GLUT_DEPTH);
}

inline void GLUT_CALL_FUNC()
{
glutDisplayFunc(display);
glutReshapeFunc(reshape);
}

inline void MY_INIT()
{
glClearColor(1.0, 1.0, 1.0, 1.0);
glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
}


int main(int argc, char **argv)
{
glutInit(&argc,argv);
GLUT_INIT();
glutCreateWindow("window name");
GLUT_CALL_FUNC();
MY_INIT();
CALC_CROSS_POINT3D();

glutMainLoop();

return 0;
}

/********[ここからコールバック]****************************************/

POINT_3D a={0,0,0},b={5,3,5};
POINT_3D p;

void display()
{

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glLoadIdentity();
gluLookAt(10.0, 15.0, 15.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);


DRAW_XYZ();


glDisable(GL_DEPTH_TEST);
glEnable(GL_BLEND);


glColor4d(0,0,1,0.5);
DRAW_PLANE();

glColor3d(0,1,0);
DRAW_LINES();

glColor3d(1,0,0);
DRAW_CROSS_POINT3D();


glEnable(GL_DEPTH_TEST);

glutSwapBuffers();

}


void reshape(int w, int h)
{
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(30.0, (double)w / (double)h, 1.0, 100.0);
glMatrixMode(GL_MODELVIEW);

}

/************** ここから各種関数 ******************/
inline void DRAW_XYZ()
{
glBegin(GL_LINES);

glColor3d(0,1,0);//x
glVertex2d(-100,0);
glVertex2d(100, 0);

glColor3d(1,0,0);//y
glVertex2d(0,0);
glVertex2d(0,100);

glColor3d(0,0,1);//z
glVertex3d(0,0,-100);
glVertex3d(0,0, 100);
glEnd();

}


inline void DRAW_PLANE()
{
glBegin(GL_TRIANGLES);
glVertex3d(5,0,0);
glVertex3d(0,5,0);
glVertex3d(0,0,5);
glEnd();
}


inline void CALC_CROSS_POINT3D()
{
POINT_3D e;
double t;

e.x = b.x - a.x;
e.y = b.y - a.y;
e.z = b.z - a.z;

t = (5-(a.x + a.y + a.z)) / (e.x + e.y + e.z);

p.x = a.x + t*e.x;
p.y = a.y + t*e.y;
p.z = a.z + t*e.z;

printf("%f,%f,%f\n",p.x,p.y,p.z);

}

inline void DRAW_CROSS_POINT3D()
{
glPointSize(2);
glBegin(GL_POINTS);
glVertex3d(p.x,p.y,p.z);
glEnd();
}

inline void DRAW_LINES()
{
glBegin(GL_LINES);
glVertex3d(a.x,a.y,a.z);
glVertex3d(b.x,b.y,b.z);
glEnd();
}