Using gluLookAt() correctly? - c

Question

I am trying to set the angle of View with gluLookAt()
Here I have my code where I tried to set the camera without results
Here the function displaycone():
void displayCone(void)
{
glMatrixMode(GL_MODELVIEW);
// clear the drawing buffer.
glClear(GL_COLOR_BUFFER_BIT);
// clear the identity matrix.
glLoadIdentity();
// traslate the draw by z = -4.0
// Note this when you decrease z like -8.0 the drawing will looks far , or smaller.
glTranslatef(0.0,0.0,-4.5);
// Red color used to draw.
glColor3f(0.8, 0.2, 0.1);
// changing in transformation matrix.
// rotation about X axis
glRotatef(xRotated,1.0,0.0,0.0);
// rotation about Y axis
glRotatef(yRotated,0.0,1.0,0.0);
// rotation about Z axis
glRotatef(zRotated,0.0,0.0,1.0);
// scaling transfomation
glScalef(1.0,1.0,1.0);
// built-in (glut library) function , draw you a Cone.
// move the peak of the cone to the origin
glTranslatef(0.0, 0.0, -height);
glutSolidCone(base,height,slices,stacks);
// Flush buffers to screen
gluLookAt(3,3,3,0,0,-4.5,0,1,0);
glFlush();
// sawp buffers called because we are using double buffering
// glutSwapBuffers();
}
With my main:
int main (int argc, char **argv)
{
glutInit(&argc, argv);
//double buffering used to avoid flickering problem in animation
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
// window size
glutInitWindowSize(400,350);
// create the window
glutCreateWindow("Cone Rotating Animation");
glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);
glClearColor(0.0,0.0,0.0,0.0);
//Assign the function used in events
glutDisplayFunc(displayCone);
glutReshapeFunc(reshapeCone);
glutIdleFunc(idleCone);
//Let start glut loop
glutMainLoop();
return 0;
}
The function idlecone instead changes the values of xRotated, yRotated... and displays the cone. Any ideas?
I am pretty sure I didn't understand the right moment where to use gluLookAt()...

Answer 1

gluLookAt changes the current matrix, similar to glTranslatef or glRotatef.
The operation defines a transformation matrix and multiplies the current matrix by the new transformation matrix.
gluLookAt has to be called before glutSolidCone, e.g.:
void displayCone(void)
{
// set matrix mode
glMatrixMode(GL_MODELVIEW);
// clear model view matrix
glLoadIdentity();
// multiply view matrix to current matrix
gluLookAt(3,3,3,0,0,-4.5,0,1,0); // <----------------------- add
// clear the drawing buffer.
glClear(GL_COLOR_BUFFER_BIT);
// traslate the draw by z = -4.0
// Note this when you decrease z like -8.0 the drawing will looks far , or smaller.
glTranslatef(0.0,0.0,-4.5);
// Red color used to draw.
glColor3f(0.8, 0.2, 0.1);
// changing in transformation matrix.
// rotation about X axis
glRotatef(xRotated,1.0,0.0,0.0);
// rotation about Y axis
glRotatef(yRotated,0.0,1.0,0.0);
// rotation about Z axis
glRotatef(zRotated,0.0,0.0,1.0);
// scaling transfomation
glScalef(1.0,1.0,1.0);
// built-in (glut library) function , draw you a Cone.
// move the peak of the cone to the origin
glTranslatef(0.0, 0.0, -height);
glutSolidCone(base,height,slices,stacks);
// Flush buffers to screen
// gluLookAt(3,3,3,0,0,-4.5,0,1,0); <----------------------- delete
glFlush();
// sawp buffers called because we are using double buffering
// glutSwapBuffers();
}