Make a camera point at a target

Question

I'm trying to point a camera to a plane I have with a texture. I'm using gluPerspective and glLookAt and this only happens when a variable is set to 1. When the variable is set to 1 I change my view:

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    gluPerspective(90.0, GLdouble(600)/GLdouble(600), 1.0, 200.0);
    gluLookAt(100.0, 50.0 + 0, 0+0, 150, 50, 0, 0.0, 1.0, 0.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

The Plane is positioned in x=500.0 , y=50.0, z=0.0

Answer 1

gluLookAt is the call you would use to do what you're asking. Before we get to that answer, however, there's are another problem to sort out first.

You initially put OpenGL into GL_PROJECTION mode, and correctly multiply a perspective matrix not the stack with your call to gluPerspective. Next you apply the matrix generated from gluLookAt also to the projection matrix stack. You don't want to do that, generally speaking. Since gluLookAt generates a viewing matrix, it really should go on the model-view matrix stack. Here's a more correct sequence of code:

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(90.0, GLdouble(600)/GLdouble(600), 1.0, 200.0);

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(100.0, 50.0 + 0, 0+0, 150, 50, 0, 0.0, 1.0, 0.0);

Now, to your question:

I'm trying to point a camera to a plane I have with a texture.

gluLookAt take three "sets" of parameters:

• the first three parameters are the position of your camera (often called eye position)
• the next three parameters are the coordinates of a point you want to look at
• the last three parameters represent a vector pointing up in your world

So, you need to choose the point on your plane that you want camera pointed toward, which you say is at (500, 50, 0), and so you'd pass those as the middle three parameters to gluLookAt. The larger question may be where you want to position the camera. If you wanted something like a "wingman view", where you're simulating flying next to the plane, you'd choose a suitable offset, say something like 20 units off the port side of the plane, and 10 units behind, flying in the same plane (geometric plane, and not airplane). You'd then set you camera position to be (500 - 20, 50 + 10, 0 + 0), and pass those three values as the first three parameters. Finally, you set the y-axis to point up, and pass those as the last parameters, as you originally did. gluLookAt will take care of generating the matrix, and applying it to the model-view matrix stack.