Projection of a Barn


Projecting a 3D barn in 2D view plan.

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#include 
#include
#include
#include

int WinWidth = 500, WinHeight = 500;

typedef struct{float x;float y;}Point2D;
typedef struct{float x;float y;float z;}Point3D;

Point3D COP = {0,0,-200}; // Centre Of Projection is at (0,0,-200)

Point3D A,B,C,D,E,F,G,H; // Vertices of the cube

Point2D Projected_A,Projected_B,Projected_C,Projected_D,Projected_E,Projected_F,Projected_G,Projected_H;

void InitCube(){
A.x = 0; A.y = 0; A.z = 0; // A(0,0,0)
B.x = 200; B.y = 0; B.z = 0; // B(200,0,0)
C.x = 200; C.y = 200; C.z = 0; // C(200,200,0)
D.x = 0; D.y = 200; D.z = 0; // D(0,200,0)

E.x = 0; E.y = 200; E.z = 200; // E(0,200,200)
F.x = 0; F.y = 0; F.z = 200; // F(0,0,200)
G.x = 200; G.y = 0; G.z = 200; // G(200,0,200)
H.x = 200; H.y = 200; H.z = 200; // H(200,200,200)
}

void DrawCube(Point2D A, Point2D B, Point2D C, Point2D D, Point2D E, Point2D F, Point2D G, Point2D H){
glPointSize(1.0);

glBegin(GL_LINE_LOOP);
//DRAWING FRONT FACE
glVertex2i(A.x, A.y); glVertex2i(B.x, B.y); glVertex2i(C.x, C.y); glVertex2i(D.x, D.y);
glEnd();

glBegin(GL_LINE_LOOP);
//DRAWING BACK FACE
glVertex2i(E.x, E.y); glVertex2i(F.x, F.y); glVertex2i(G.x, G.y); glVertex2i(H.x, H.y);
glEnd();

glBegin(GL_LINES);
//DRAWING OTHER LINES
glVertex2i(A.x, A.y); glVertex2i(F.x, F.y);

glVertex2i(B.x, B.y); glVertex2i(G.x, G.y);

glVertex2i(C.x, C.y); glVertex2i(H.x, H.y);

glVertex2i(D.x, D.y); glVertex2i(E.x, E.y);
glEnd();

glFlush();
}

Point2D Project_Perspective(Point3D p, Point3D CoP){
Point2D p2;
float d = abs(CoP.z); // The distance between the COP and orign

p2.x = d*(p.x)/(p.z+d);
p2.y = d*(p.y)/(p.z+d);

//.....wite necessary equations here for perspective transformation

return p2;
}

Point2D translate2D(Point2D p, float tx, float ty){
Point2D tp2;
tp2.x = p.x + tx;
tp2.y = p.y + ty;

return tp2;
}

Point3D translate3D(Point3D p, float tx, float ty, float tz){
Point3D tp3;
//.....wite the equations for 3D translation
tp3.x = p.x + tx;
tp3.y = p.y + ty;
tp3.z = p.z + tz;
return tp3;
}

void Draw3DTranslation(){
glClearColor(1.0f, 1.0f, 1.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(0.0f, 0.0f, 0.0f);

Point3D COP ={100,100,-200};
A = translate3D(A,-100,-100,200);
B = translate3D(B,-100,-100,200);
C = translate3D(C,-100,-100,200);
D = translate3D(D,-100,-100,200);
E = translate3D(E,-100,-100,200);
F = translate3D(F,-100,-100,200);
G = translate3D(G,-100,-100,200);
H = translate3D(H,-100,-100,200);

Projected_A = Project_Perspective(A,COP);
Projected_B = Project_Perspective(B,COP);
Projected_C = Project_Perspective(C,COP);
Projected_D = Project_Perspective(D,COP);
Projected_E = Project_Perspective(E,COP);
Projected_F = Project_Perspective(F,COP);
Projected_G = Project_Perspective(G,COP);
Projected_H = Project_Perspective(H,COP);

//2D Translation to Move Projected to Center Screen
Projected_A = translate2D(Projected_A,WinWidth/2,WinHeight/2);
Projected_B = translate2D(Projected_B,WinWidth/2,WinHeight/2);
Projected_C = translate2D(Projected_C,WinWidth/2,WinHeight/2);
Projected_D = translate2D(Projected_D,WinWidth/2,WinHeight/2);
Projected_E = translate2D(Projected_E,WinWidth/2,WinHeight/2);
Projected_F = translate2D(Projected_F,WinWidth/2,WinHeight/2);
Projected_G = translate2D(Projected_G,WinWidth/2,WinHeight/2);
Projected_H = translate2D(Projected_H,WinWidth/2,WinHeight/2);

DrawCube(Projected_A,Projected_B,Projected_C,Projected_D,Projected_E,Projected_F,Projected_G,Projected_H);
}

void keyboard(unsigned char key, int x, int y)
{
if (key == 'q' || key == 'Q')
exit(EXIT_SUCCESS);
}

void myMouse(int button, int state, int x, int y) {
if(state == GLUT_DOWN)
{
if(button == GLUT_LEFT_BUTTON)
{

}
else if (button == GLUT_RIGHT_BUTTON)
{
Draw3DTranslation();
}
}
}

void myDisplay()
{
glClearColor(1.0f, 1.0f, 1.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(0.0f, 0.0f, 0.0f);

Projected_A = Project_Perspective(A,COP);
Projected_B = Project_Perspective(B,COP);
Projected_C = Project_Perspective(C,COP);
Projected_D = Project_Perspective(D,COP);
Projected_E = Project_Perspective(E,COP);
Projected_F = Project_Perspective(F,COP);
Projected_G = Project_Perspective(G,COP);
Projected_H = Project_Perspective(H,COP);

//TRANSLATE TO MID POINT OF THE SCREEN
Projected_A = translate2D(Projected_A,WinWidth/2,WinHeight/2);
Projected_B = translate2D(Projected_B,WinWidth/2,WinHeight/2);
Projected_C = translate2D(Projected_C,WinWidth/2,WinHeight/2);
Projected_D = translate2D(Projected_D,WinWidth/2,WinHeight/2);
Projected_E = translate2D(Projected_E,WinWidth/2,WinHeight/2);
Projected_F = translate2D(Projected_F,WinWidth/2,WinHeight/2);
Projected_G = translate2D(Projected_G,WinWidth/2,WinHeight/2);
Projected_H = translate2D(Projected_H,WinWidth/2,WinHeight/2);

DrawCube(
// Calculate the following values
Projected_A,
Projected_B,
Projected_C,
Projected_D,
Projected_E,
Projected_F,
Projected_G,
Projected_H
);


}


int main( int argc, char ** argv ) {
glutInit( &argc, argv );
glutInitWindowPosition( 0, 0 );
glutInitWindowSize( WinWidth, WinHeight );
glutCreateWindow( "Projection of a Cube" );

glMatrixMode( GL_PROJECTION );
glLoadIdentity();
gluOrtho2D( 0, WinWidth, 0, WinHeight );
glViewport(0, 0, WinWidth, WinHeight);

InitCube();

glutKeyboardFunc(keyboard);
glutMouseFunc( myMouse );
glutDisplayFunc( myDisplay );
glutMainLoop();

return( 0 );
}
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