I don't have much OpenGL experience. I am trying to draw a teapot and move a camera around the teapot. To this end I am using the gluLookAt function. The problem is that when I call gluLookAt the screen is blank and I can't see my teapot.
#include "openGLer.h"
void openGLer::simulate(grid* toSim, int* argc, char** argv)
{
myGrid = toSim;
glutInit(argc, argv);
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowSize(400, 400); //Set the window size
glutCreateWindow("");
glutDisplayFunc(display);
glutIdleFunc(display);
glutKeyboardFunc(handleKeypress);
glEnable(GL_DEPTH_TEST);
glutMainLoop();
}
void openGLer::handleKeypress(unsigned char key, //The key that was pressed
int x, int y)
{
switch (key)
{
case 27: exit(0);
}
}
void openGLer::camera()
{
gluLookAt(3, 3, 0,
0, 0, 0,
0, 1, 0
);
}
void openGLer::draw()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
camera();
glutWireTeapot(0.5);
glutSwapBuffers();
}
void openGLer::display()
{
draw();
}
Why does gluLookAt() make the screen blank and how do I fix this? When camera() is not called code performs as expected; with a teapot being displayed.
Have you set up your projection matrix correctly? Otherwise, your call to gluLookAt will cause the teapot to be too far away and therefore be clipped by the far plane.
Try adding this to your initialization code (and also your resize handler to fix the aspect ratio when the window is resized). I've set the far plane at 100, which should be plenty for your teapot.
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective (60.0, width/(float)height, 0.1, 100.0);
glMatrixMode(GL_MODELVIEW);
Related
I follow the code tutorial from the OpenGL programming book, but it doesn't work. It is showing white rectangle at the top left of my window. Could you please tell me what could be wrong with it?
#include<windows.h>
#include <GL/glut.h>
float yRot=0.0;
void Render()
{
//clear color and depth buffer
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();//load identity matrix
glTranslatef(0.0f,0.0f,-4.0f);//move forward 4 units
//rotate along the y-axis
glRotatef(yRot,0.0f,1.0f,0.0f);
glColor3f(0.0f,0.0f,1.0f); //blue color
glBegin(GL_POLYGON);//begin drawing of polygon
glVertex3f(-0.5f,0.5f,0.0f);//first vertex
glVertex3f(0.5f,0.5f,0.0f);//second vertex
glVertex3f(1.0f,0.0f,0.0f);//third vertex
glVertex3f(0.5f,-0.5f,0.0f);//fourth vertex
glVertex3f(-0.5f,-0.5f,0.0f);//fifth vertex
glVertex3f(-1.0f,0.0f,0.0f);//sixth vertex
glEnd();//end drawing of polygon
yRot+=0.1f;//increment the yRot variable
}
//method the reshape the entire figure.
void reshape(int x, int h){
glViewport(0,0,x,h);
}
void init()
{
glClearColor(0.0,0.0,0.2,0.8);
}
int main(int argc, char** argv)
{
glutCreateWindow("simple triangles");
glutDisplayFunc(Render);
glutReshapeFunc(reshape);
init();
glutMainLoop();
}
First of all, you're not calling glutInit(&argc, argv) in main() before all the other GLUT related calls. Second of all, you're not calling glutSwapBuffers() in Render().
Besides that you aren't changing the projection matrix, and thus don't have the same resize function as the one presented in the beginning of the tutorial.
void Resize(int width, int height)
{
glViewport(0, 0, (GLsizei)width, (GLsizei)height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f, (GLfloat)width / (GLfloat)height, 1.0f, 1000.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
Changing those things and your code should work.
I want to make a space invader game in opengl. So I thought of creating the enemies using triangles. Before making the game, I want to try out my hand in animation. I have triangle. i want to translate it left upto some point with animation(i.e, triangle is translated after some interval of time. It should look as if it is moving).After reaching some point in the left, I want to translate it back to the same position or some distances right. The process should go on till the screen is open. I used sleep function. But it is not working. No animation is shown. Only the translated triangle is drawn at different translated position. Help me.
Here is my code-
#include "windows.h"
#include <gl/glut.h>
#include<stdio.h>
void init( void )
{
printf( "OpenGL version: %s\n", (char*)glGetString(GL_VERSION));
printf( "OpenGL renderer: %s\n", (char*)glGetString(GL_RENDERER));
//Configure basic OpenGL settings
glClearColor(1.0, 1.0, 0.0, 0.0);
glMatrixMode(GL_PROJECTION);
gluOrtho2D(0.0,640.0,0.0,480.0);
glColor3f(1.0,0.0,0.0);
glPointSize(3);
}
void house(int x, int y,int z)
{
glPushMatrix();
glTranslatef(x, y,z);
glBegin (GL_LINES);
glVertex2i (0,30);
glVertex2i (15,60);
glVertex2i (15,60);
glVertex2i (30,30);
glVertex2i (30,30);
glVertex2i (0,30);
glEnd();
//Sleep(200);
glPopMatrix();
//glutSwapBuffers();
}
// Main drawing routine. Called repeatedly by GLUT's main loop
void display( void )
{
//Clear the screen and set our initial view matrix
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
int i;
for(i = 10; i < 350; i = i + 50)
{
house(i,20,0);
Sleep(200);
}
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glFlush();
}
// Entry point - GLUT setup and initialization
int main( int argc, char** argv )
{
glutInit( &argc, argv );
glutInitDisplayMode (GLUT_DEPTH | GLUT_SINGLE| GLUT_RGB);
glutInitWindowSize (800, 600);
glutInitWindowPosition (100, 100);
glutCreateWindow( "OpenGL Test" );
glutDisplayFunc( display );
init();
glutMainLoop();
return 0;
}
In main() you have declared your display() as display callback function. GLUT will call this function either when it determines that the window need to be redrawn or when it is told to redraw it for example by the function glutPostRedisplay().
The display function is expected to call redraw the windows at a specific point in time. The glFlush() will force the execution of the GL commands.
The problem is that your animation loop is inside the redraw function and glFlush() is called at the end, showing the result at once. And you don't tell GLUT to redraw the windows. This is why you don't seee the animation.
For the purpose of the tutorial, I propose you to define a global variable for the initial position of the house drawing. Of course, you'll have to improve this as soon as you understood how all this works.
static int pos = 10; // temporary work around, just for the demo
Then define a timer function, that gets called after a time interval. This will be the core of your animation, organizing the moving, and the redrawing of the window by calling glutPostRedisplay() :
void timerfunc(int value) // handle animation
{
pos += 50; // update the postion
if (pos<350) // as in your originial loop
glutTimerFunc(200, timerfunc, 0); // plan next occurence
glutPostRedisplay(); // redraw the window
}
Activate your timer function, in main() just before launching glutMainLoop():
glutTimerFunc(200, timerfunc, 0); // call a timer function
glutMainLoop(); // this call is already in your code
Your display function can then be changed into:
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
house(pos, 20, 0); // draw the house at its last calculated position
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glFlush();
}
Then it works in animated modus !
Main function:
int _tmain(int argc, char* argv[])
{
glutInit(&argc, argv);
glutInitWindowSize (500, 500);
glutInitDisplayMode (GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH );
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LESS);
glutInitWindowPosition (700, 100);
glutCreateWindow("Result");
glutDisplayFunc(display2);
glutReshapeFunc(reshape2);
glutMouseFunc(main_mouse);
glutKeyboardFunc(keyboard);
glutMainLoop();
return 0;
}
Display2 function:
void display2()
{
glClearColor(1.0,1.0,1.0,1.0);
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
//Green square
glColor3f(0.0,1.0,0.0);
glBegin(GL_POLYGON);
glVertex3f(0.5,0.5,-1.0);
glVertex3f(0.5,1.5,-1.0);
glVertex3f(1.5,1.5,-1.0);
glVertex3f(1.5,0.5,-1.0);
glEnd();
//Red square
glColor3f(1.0,0.0,0.0);
glBegin(GL_POLYGON);
glVertex3f(0.0,0.0,-2.0);
glVertex3f(0.0,1.0,-2.0);
glVertex3f(1.0,1.0,-2.0);
glVertex3f(1.0,0.0,-2.0);
glEnd();
glutSwapBuffers();
}
reshape2 function
void reshape2(int width, int height)
{
glViewport(0,0,width,height);
glMatrixMode(GL_PROJECTION);
glOrtho(-3.0,3.0,-3.0,3.0,0.01,3.0);
}
I have problem with depth buffer in openGL. I try to draw 2 square red and green. The red one is located behind the green one.
Red square have z value -2 while green square have z value -1. But the red square displayed at front of green square. I have enabled the depth test but still not work. What is wrong with my program?
Don't call any gl* function before you call glutCreateWindow, so move glEnable and glDepthFunc after it.
Every gl functions make calls to the context which is only created with the GLUT window. No OpenGL functions is effective before that.
I'm trying to load 3D models from .obj format and it draws the object on the scren without any problem but when I resize the screen everything disappear. Here's the code:
Obj* object = new Obj();
GLuint texture[1];
void handleResize(int w, int h) {
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0,(double)w / (double)h,1.0,200.0);
}
void initRendering() {
object->GetObj("cube.obj");
glShadeModel(GL_LINEAR);
glClearColor(0.0f, 0.0f, 0.0f, 0.5f);
glEnable(GL_DEPTH_TEST);
}
void handleKeypress(unsigned char key, int x, int y) {
switch (key) {
case 27:
{
exit(0);
break;
}
}
}
void drawScene()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPushMatrix();
glRotatef(45.0,0.0,1.0,0.0);
object->DrawObj();
glPopMatrix();
glutSwapBuffers();
glFlush();
}
int _tmain(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(400, 400);
glutCreateWindow("3D");
initRendering();
glutReshapeFunc(handleResize);
glutDisplayFunc(drawScene);
glutKeyboardFunc(handleKeypress);
glutMainLoop();
return 0;
}
And here's the code for Obj.DrawObj():
glBegin(GL_TRIANGLES);
for(int i = 0;i < faces.capacity()-1;i++)
{
glVertex3f(vertices[faces[i].vertex1].cordinate1,vertices[faces[i].vertex1].cordinate2,vertices[faces[i].vertex1].cordinate3);
glVertex3f(vertices[faces[i].vertex2].cordinate1,vertices[faces[i].vertex2].cordinate2,vertices[faces[i].vertex2].cordinate3);
glVertex3f(vertices[faces[i].vertex3].cordinate1,vertices[faces[i].vertex3].cordinate2,vertices[faces[i].vertex3].cordinate3);
}
glEnd;
In your drawing code you set the projection matrix, which is good. However you set it to identity. In the resize handler you're setting the projection matrix as well, but you shouldn't do it there; yes I know the tutorials have it all there, but this is very bad style. You should move all the code currently in the reshape handler into the drawing handler, replacing the current setting of the projection matrix.
I can see that you're still confused by reading your PasteBin. Let me try to explain:
The reason why you can see your object the first time you draw it is because you have not set a projection matrix. So your object is drawn directly in normalized device coordinates (-1 to 1 range).
When you resize, you're setting the projection matrix for the first time, and this changes what viewing region is drawn to your screen. Your object as it is initially drawn is outside of the viewing region defined by your projection matrix (it is on top of the camera and I guess in front of the near plane. You have to move the object back away from the camera so that it is inside the view frustum. This is what datenwolf was suggesting.
However at the same time you introduced other errors into your code, particularly that you stopped resetting the projection matrix in handleResize. You have to always clear the projection matrix before you call gluPerspective, or else you will get a bogus result.
If you take the exact code from your pastebin, and add a glLoadIdentity to handleResize, I think that should work then:
void handleResize(int w, int h) {
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION); //<--- add
glLoadIdentity(); //<--- add
gluPerspective(45.0,(double)w / (double)h,1.0,200.0);
}
Also, you're still clearing the projection matrix during the drawScene function. When you clear the matrix, you're throwing away the perspective setting that you just set in handleResize, you don't want to do that.
So basically:
Set the Projection matrix in handleResize and on initialization
Don't touch the projection matrix in drawScene
Translate the object so that it fits into the viewing frustum.
I have written a simple OpenGL program in C++ that displays a line joining the center of the window to the current position of the mouse pointer.
My code is :
#ifdef __APPLE__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif
#include<iostream>
using namespace std;
void passive(int,int);
void reshape(int,int);
void init(void);
void display(void);
void camera(void);
int x=3,y=3;
int main (int argc,char **argv) {
glutInit (&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_DEPTH | GLUT_RGBA);
glutInitWindowSize(1364,689);
glutInitWindowPosition(0,0);
glutCreateWindow("Sample");
init();
glutDisplayFunc(display);
glutIdleFunc(display);
glutPassiveMotionFunc(passive);
glutReshapeFunc(reshape);
glutMainLoop();
return 0;
}
void display(void) {
glClearColor (0.0,0.0,0.0,1.0);
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
camera();
glBegin(GL_LINES);
glVertex3f(0,0,0);
glVertex3f(x,y,0);
glEnd();
glutSwapBuffers();
}
void camera(void) {
glRotatef(0.0,1.0,0.0,0.0);
glRotatef(0.0,0.0,1.0,0.0);
glTranslated(0,0,-20);
}
void init(void) {
glEnable (GL_DEPTH_TEST);
glEnable (GL_BLEND);
glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_COLOR_MATERIAL);
}
void reshape(int w, int h) {
glViewport(0,0,(GLsizei)w,(GLsizei)h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60,(GLfloat)w/(GLfloat)h,1.0,100.0);
glMatrixMode(GL_MODELVIEW);
}
void passive(int x1,int y1) {
x=x1; y=y1;
}
The problem I am facing is that the x and y values set in the passive() function is not correctly mapped into the screen which uses perspective projection. So the line drawn is joining the center to some other coordinate outside the screen. Any modifications to the code to get it working properly?
An easy way would be to create an orthographic projection matrix and then render all of your "2D" elements (including this line, using the screen coordinates provided by glutPassiveMotionFunc).
Something like this:
void display() {
// clear
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective( ... ) // create 3D perspective projection matrix
glMatrixMode(GL_MODELVIEW);
// Render 3D content here
// Render 2D content
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, width, height, 0); // create 2D orthographic projection matrix with coordinate system roughly equivalent to window position
glMatrixMode(GL_MODELVIEW);
glBegin(GL_LINES);
glVertex2f( width / 2, height / 2 ); // now we can use "pixel coordinates"
glVertex2f( cursorX, cursorY );
glEnd();
...
}
Compare this to your modification of the perspective projection in your reshape method.
Obviously you'll also want to disable states that don't make sense for a "2D" rendering (like depth buffer checking, etc) but it should be pretty obvious. Take a look at this GDSE post for a discussion of how other people do this same task.