OpenGL true coordinates and glutTimerFunc() problem C++ - c++

Question

HI I am starting to learn openGl for C++.but at stating point I stucked.
I have 2 question that is the coordinates for drawing some objects? I mean where is X, Y and Z?
Second one I am making tutorial from some sites. and I am trying to animate my triangle.In tutorial it works but on my computer not.I Also downloaded source codes but It doesnt move. And there is no compiler error.
Edit:I solved problem. With restarting computer.I think it is poblem about my computer.
Here sample codes. I thougt that problem is glutTimerFunc().
#include <iostream>
#include <stdlib.h>
#ifdef __APPLE__
#include<OpenGL/OpenGL.h>
#include <GLUT/glut.h>
#else
#include <gl/glut.h>
#endif
using namespace std;
//Called when a key is pressed
void handleKeypress(unsigned char key, int x, int y) {
switch (key) {
case 27: //Escape key
exit(0);
}
}
//Initializes 3D rendering
void initRendering() {
glEnable(GL_DEPTH_TEST);
}
//Called when the window is resized
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);
}
float _angle = 30.0f;
float _cameraAngle = 0.0f;
//Draws the 3D scene
void drawScene() {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW); //Switch to the drawing perspective
glLoadIdentity(); //Reset the drawing perspective
glRotatef(-_cameraAngle, 0.0f, 1.0f, 0.0f); //Rotate the camera
glTranslatef(0.0f, 0.0f, -5.0f); //Move forward 5 units
glPushMatrix(); //Save the transformations performed thus far
glTranslatef(0.0f, -1.0f, 0.0f); //Move to the center of the trapezoid
glRotatef(_angle, 0.0f, 0.0f, 1.0f); //Rotate about the z-axis
glBegin(GL_QUADS);
//Trapezoid
glVertex3f(-0.7f, -0.5f, 0.0f);
glVertex3f(0.7f, -0.5f, 0.0f);
glVertex3f(0.4f, 0.5f, 0.0f);
glVertex3f(-0.4f, 0.5f, 0.0f);
glEnd();
glPopMatrix(); //Undo the move to the center of the trapezoid
glPushMatrix(); //Save the current state of transformations
glTranslatef(1.0f, 1.0f, 0.0f); //Move to the center of the pentagon
glRotatef(_angle, 0.0f, 1.0f, 0.0f); //Rotate about the y-axis
glScalef(0.7f, 0.7f, 0.7f); //Scale by 0.7 in the x, y, and z directions
glBegin(GL_TRIANGLES);
//Pentagon
glVertex3f(-0.5f, -0.5f, 0.0f);
glVertex3f(0.5f, -0.5f, 0.0f);
glVertex3f(-0.5f, 0.0f, 0.0f);
glVertex3f(-0.5f, 0.0f, 0.0f);
glVertex3f(0.5f, -0.5f, 0.0f);
glVertex3f(0.5f, 0.0f, 0.0f);
glVertex3f(-0.5f, 0.0f, 0.0f);
glVertex3f(0.5f, 0.0f, 0.0f);
glVertex3f(0.0f, 0.5f, 0.0f);
glEnd();
glPopMatrix(); //Undo the move to the center of the pentagon
glPushMatrix(); //Save the current state of transformations
glTranslatef(-1.0f, 1.0f, 0.0f); //Move to the center of the triangle
glRotatef(_angle, 1.0f, 2.0f, 3.0f); //Rotate about the the vector (1, 2, 3)
glBegin(GL_TRIANGLES);
//Triangle
glVertex3f(0.5f, -0.5f, 0.0f);
glVertex3f(0.0f, 0.5f, 0.0f);
glVertex3f(-0.5f, -0.5f, 0.0f);
glEnd();
glPopMatrix(); //Undo the move to the center of the triangle
glutSwapBuffers();
}
void update(int value) {
_angle += 2.0f;
if (_angle > 360) {
_angle -= 260;
}
glutPostRedisplay(); //Tell GLUT that the display has changed
//Tell GLUT to call update again in 25 milliseconds
glutTimerFunc(25, update, 0);
}
int main(int argc, char** argv) {
//Initialize GLUT
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(400, 400);
//Create the window
glutCreateWindow("Transformations and Timers - videotutorialsrock.com");
initRendering();
//Set handler functions
glutDisplayFunc(drawScene);
glutKeyboardFunc(handleKeypress);
glutReshapeFunc(handleResize);
glutTimerFunc(24, update, 0); //Add a timer
glutMainLoop();
return 0;
}

Answer 1

Regarding your first question, you can use gluProject() to apply your transform matrices (via GL_MODELVIEW_MATRIX and GL_PROJECTION_MATRIX) to arbitrary vertexes.