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Darius
10-15-2012, 01:38 PM
Hi,

I am new to OpenGL. I am trying to make a motorcycle with primitive shapes. For some reason, the shapes that I have made are see-through and I can't figure out why. I am not specifying any alpha anywhere; here is my code:


#include <GL/glut.h>
#include <math.h>

GLUquadricObj *quadratic;
static int isWire = 0; // Is wireframe?
static int distance = 10;
static float angleH = 0;
static float angleV = 0;

static float R = 2.0; // Radius of hemisphere.
static int p = 4; // Number of longitudinal slices.
static int q = 6; // Number of latitudinal slices.

#define PI 3.14159265358979324

static unsigned int pipe, seat, cover, wheel, wheelCenter, cycles; // parts of the motorcycle to make as display lists.
GLUquadricObj *cylinder;

void drawCoordinates();
void drawMotorcycle();
void drawTrailer();
void drawHemisphere();
void drawCylinder(float x, float y, float z);
void drawHandle(float x, float y, float z);
void drawLight();
void drawBase();
void setup();

void display () {

/* clear window */
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

gluLookAt(distance*cos(angleH), distance*cos(angleV), distance*sin(angleH), 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

/* future matrix manipulations should affect the modelview matrix */
glMatrixMode(GL_MODELVIEW);

if (isWire) glPolygonMode(GL_FRONT_AND_BACK, GL_LINE); else glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);

glPushMatrix();

drawCoordinates();

glPushMatrix();
glTranslatef(0.0, 0.0, 0.0); // Move the motorcycle around the world space
drawMotorcycle();
drawTrailer();
glPopMatrix();

glPopMatrix();

/* flush drawing routines to the window */
glFlush();
}

void drawCoordinates()
{
/***************** DRAW AXIS *****************/
glPushMatrix();
GLUquadricObj *xAxis;
xAxis=gluNewQuadric();
glColor3f(1,0,0);
glRotatef(-90, 0, 1, 0);
gluCylinder(xAxis,0.05,0.05,1,5,5);
glPopMatrix();

glPushMatrix();
GLUquadricObj *yAxis;
yAxis=gluNewQuadric();
glColor3f(0,1,0);
glRotatef(-90, 1, 0, 0);
gluCylinder(yAxis,0.05,0.05,1,5,5);
glPopMatrix();

glPushMatrix();
GLUquadricObj *zAxis;
zAxis=gluNewQuadric();
glColor3f(0,0,1);
gluCylinder(zAxis,0.05,0.05,1,5,5);
glPopMatrix();
/***************** END OF DRAW AXIS *****************/
}

void drawMotorcycle()
{
//DRAW ENGINE
glPushMatrix();
//drawCoordinates();
glColor3f(.6, 0, 0);
glScalef(1.4, 0.8, 1.0);
glutSolidSphere(1,8,8);
glPushMatrix();
//drawCoordinates();
glPopMatrix();
glPopMatrix();

//DRAW PIPES UNDER ENGINE
glPushMatrix();
glRotatef(-90, 1, 0, 0);
glRotatef(80, 0, 1, 0);
glTranslatef(0.5, 1.0, -1.5);
glCallList(pipe);
glTranslatef(0.0, -2.0, 0.0);
glCallList(pipe);
glPopMatrix();

//DRAW SEAT
glPushMatrix();
glPushMatrix();
glRotatef(15, 0, 0, 1);
glTranslatef(-2.0, -0.4, 0.0);
glScalef(2.0, 0.2, 1.2);
glCallList(seat);
glPopMatrix();

//DRAW BACK SEAT
glRotatef(-40, 0, 0, 1);
glTranslatef(-2.3, -2.8, 0.0);
glScalef(2.0, 0.2, 1.2);
glCallList(seat);
glPopMatrix();

//DRAW FRONT PLATE
glPushMatrix();
glRotatef(120, 0, 0, 1);
glTranslatef(0.8, -1.3, 0.0);
glScalef(2.0, 0.2, 1.35);
glColor3f(0.5,0.0,0.0);
glutSolidCube(1);
glPushMatrix();
//drawCoordinates();
glPopMatrix();
glPopMatrix();

//DRAW FRONT PIPES
glPushMatrix();
glRotatef(-90, 1, 0, 0);
glRotatef(-30, 0, 1, 0);
glTranslatef(1.3, -0.9, -5.7);
glScalef(1.0, 1.0, 2.5);
glCallList(pipe);
glTranslatef(0.0, 1.7, 0.0);
glCallList(pipe);
glPopMatrix();

//DRAW WHEEL COVERS
glPushMatrix();
glTranslatef(3.5, -3.0, 0.0);
glScalef(1.0, 0.5, 1.0);
glRotatef(45, 0, 0, 1);
glCallList(cover);
glTranslatef(-5.5, 0.0, 0.0);
glRotatef(-100, 0, 0, 1);
glTranslatef(-8.5, 0.2, 0.0);
glCallList(cover);
glPopMatrix();

//DRAW WHEELS
glPushMatrix();
glTranslatef(3.9, -4.1, 0.0);
glCallList(wheel);
glTranslatef(-9.2, 2.0, 0.0);
glCallList(wheel);
glPopMatrix();

//DRAW WHEEL CENTER PIECES
glPushMatrix();
glTranslatef(3.9, -4.1, 0.0);
glCallList(wheelCenter);
glTranslatef(-9.2, 2.0, 0.0);
glCallList(wheelCenter);
glPopMatrix();

//DRAW CYCLES AROUND WHEELS
glPushMatrix();
glTranslatef(3.9, -4.1, 0.0);
glRotatef(-90, 1, 0, 0);

for(int i=0; i<8; i++)
{
glRotatef(45, 0, 1, 0);
glPushMatrix();
glCallList(cycles);
glPopMatrix();
}

glTranslatef(-9.2, 0.0, 2.0);

for(int i=0; i<8; i++)
{
glRotatef(45, 0, 1, 0);
glPushMatrix();
glCallList(cycles);
glPopMatrix();
}
glPopMatrix();

//DRAW HANDLE BARS
glPushMatrix();
glTranslatef(0.2, 2.0, 0.0);
glRotatef(-45, 1, 0, 0);
glScalef(0.7, 0.7, 0.7);
glCallList(pipe);
glRotatef(-90, 1, 0, 0);
glCallList(pipe);
glPopMatrix();

//DRAW LIGHT
glPushMatrix();
glTranslatef(1.0, 1.0, 0.0);
glColor3f(0.5, 0.5, 0.0);
//glScalef(1.0, 0.5, 1.0);
glutSolidSphere(0.5, 5, 5);
glPushMatrix();
//drawCoordinates();
glPopMatrix();
glPopMatrix();

//DRAW BASE
glPushMatrix();
glRotatef(10.0, 0.0, 0.0, 1.0);
glScalef(3.5, 1.5, 1.0);
glTranslatef(-0.4, -1.0, 0.0);
glColor3f(0.3, 0.3, 0.3);
glutSolidCube(1);
glPopMatrix();

//GAS TANK
glPushMatrix();
glScalef(2.5, 1.0, 0.8);
glTranslatef(-0.8, -1.7, -1.4);
glCallList(pipe);
glPopMatrix();
}

void drawTrailer()
{
//DRAW BODY
glPushMatrix();
glColor3f(0.0, 0.0, 0.3);
glScalef(2.0, 2.5, 1.5);
glTranslatef(-4.5, -0.5, 0.0);
glutSolidCube(1);
glPopMatrix();

//DRAW WHEELS
glPushMatrix();
glPushMatrix();
glScalef(0.8, 0.8, 0.8);
glTranslatef(-12.0, -1.5, 2.0);
glCallList(wheel);
glCallList(wheelCenter);

glRotatef(90, 1, 0, 0);
for(int i=0; i<8; i++)
{
glRotatef(45, 0, 1, 0);
glPushMatrix();
glCallList(cycles);
glPopMatrix();
}
glPopMatrix();

glPushMatrix();
glScalef(0.8, 0.8, 0.8);
glTranslatef(-12.0, -1.5, -2.0);
glCallList(wheel);
glCallList(wheelCenter);

glRotatef(90, 1, 0, 0);
for(int i=0; i<8; i++)
{
glRotatef(45, 0, 1, 0);
glPushMatrix();
glCallList(cycles);
glPopMatrix();
}
glPopMatrix();
glPopMatrix();

//DRAW CONNECTION TO MOTORCYCLE
glPushMatrix();
glRotatef(90, 0, 1, 0);
glTranslatef(0.0, -1.0, -8.0);
glCallList(pipe);
glPopMatrix();
}

void drawHemisphere()
{
for(int j = 0; j < q; j++)
{
// One latitudinal triangle strip.
glBegin(GL_TRIANGLE_STRIP);
for(int i = 0; i <= p; i++)
{
glVertex3f( R * cos( (float)(j+1)/q * PI/2.0 ) * cos( 2.0 * (float)i/p * PI ),
R * sin( (float)(j+1)/q * PI/2.0 ),
R * cos( (float)(j+1)/q * PI/2.0 ) * sin( 2.0 * (float)i/p * PI ) );
glVertex3f( R * cos( (float)j/q * PI/2.0 ) * cos( 2.0 * (float)i/p * PI ),
R * sin( (float)j/q * PI/2.0 ),
R * cos( (float)j/q * PI/2.0 ) * sin( 2.0 * (float)i/p * PI ) );
}
glEnd();
}
}

void reshape (int w, int h)
{

// (Window of width = zero is not possible).
if(h == 0)
h = 1;

float ratio = 1.0* w / h;

// Reset the coordinate system before modifying
glMatrixMode(GL_PROJECTION);
glLoadIdentity();

// Set the viewport to be the entire window
glViewport(0, 0, w, h);

// Set the correct perspective.
gluPerspective(90,ratio,-1,1);
}


// Keyboard input processing routine.
void keyInput(unsigned char key, int x, int y)
{
switch(key)
{
case 'c' : distance = 10; angleH=0; angleV=0.0; break;
case 'C' : distance = 10; angleH=0; angleV=0.0; break;
case 'f': distance = (distance == 4)? 4:distance-1; break;
case 'F': distance = (distance == 4)? 4:distance-1; break;
case 'b': distance = (distance == 20)? 20:distance+1; break;
case 'B': distance = (distance == 20)? 20:distance+1; break;
case 'w': if (isWire == 0) isWire = 1; else isWire = 0; break;
case 'W': if (isWire == 0) isWire = 1; else isWire = 0; break;
//case 27: exit(0); break;
default: break;
}
}

void specialKeyboard(int key, int x, int y) {
switch (key)
{
case GLUT_KEY_RIGHT:
angleH -= .2;
break;
case GLUT_KEY_LEFT:
angleH += .2;
break;
case GLUT_KEY_UP:
angleV += .2;
break;

case GLUT_KEY_DOWN:
angleV -= .2;
break;
}

}

void update(void){
glutPostRedisplay();
}

void setup()
{
// PARTS
pipe = glGenLists(1);
seat = glGenLists(1);
cover = glGenLists(1);
wheel = glGenLists(1);
wheelCenter = glGenLists(1);
cycles = glGenLists(1);

glNewList(pipe, GL_COMPILE); // Any cylinder on the motorcycle
GLUquadricObj *cylinder;
cylinder=gluNewQuadric();
glPushMatrix();
glColor3f(.5,.5,.5);
gluCylinder(cylinder,0.2,0.2,3,5,5);
glPushMatrix();
//drawCoordinates();
glPopMatrix();
glPopMatrix();
glEndList();

glNewList(seat, GL_COMPILE);
glPushMatrix();
glColor3f(0.5, 0.35, 0.05);
glutSolidCube(1);
glPushMatrix();
//drawCoordinates();
glPopMatrix();
glPopMatrix();
glEndList();

glNewList(cover, GL_COMPILE);
glPushMatrix();
glColor3f(0.5, 0.0, 0.0);
drawHemisphere();
glPushMatrix();
//drawCoordinates();
glPopMatrix();
glPopMatrix();
glEndList();

glNewList(wheel, GL_COMPILE);
glPushMatrix();
glColor3f(0.1, 0.1, 0.1);
glutSolidTorus(0.2, 1.2, 20, 20);
glPushMatrix();
//drawCoordinates();
glPopMatrix();
glPopMatrix();
glEndList();

glNewList(wheelCenter, GL_COMPILE);
glPushMatrix();
glColor3f(0.4, 0.5, 0.5);
glScalef(1.0, 0.5, 1.0);
glutSolidSphere(0.8, 5, 5);
glPushMatrix();
//drawCoordinates();
glPopMatrix();
glPopMatrix();
glEndList();

glNewList(cycles, GL_COMPILE);
glColor3f(0.5, 0.5, 0.5);
glScalef(0.25, 0.25, 0.25);
cylinder=gluNewQuadric();
gluCylinder(cylinder,0.5,0.5,5,15,5);
glEndList();
}


int main (int argc, char** argv) {

/* initialize GLUT, using any commandline parameters passed to the
program */
glutInit(&argc,argv);

/* setup the size, position, and display mode for new windows */
glutInitWindowSize(500,500);
glutInitWindowPosition(0,0);
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );

/* create and set up a window */
glutCreateWindow("Motorcycle");
setup(); // Build all the display lists, ready to use

glutIdleFunc(update);
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutKeyboardFunc(keyInput);
glutSpecialFunc(specialKeyboard);

/* set up depth-buffering */
glEnable(GL_DEPTH_TEST);

/* background color */
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

/* tell GLUT to wait for events */
glutMainLoop();
return 0;
}

You can rotate the camera with the arrow keys to see that the objects are see through. How can I fix this? I would also appreciate any advice to improve my code in any way, I want to learn as much as I can about OpenGL. Any advice would be appreciated.

tonyo_au
10-16-2012, 04:11 PM
Hi,

You can rotate the camera with the arrow keys to see that the objects are see through.

I you mean they disappear as you rotate it might be from culling back faces; try disabling culling with glDisable(GL_CULL_FACE)

Darius
10-22-2012, 02:47 PM
It was actually because my gluPerspective(90,ratio,-1,1) statement was wrong. I changed it to gluPerspective(90,ratio, 1, 100) and it's fine now. Thanks.