# gluLookAt causes blank screen [closed]

I'm doing a C++ exercise for university. Basically it's supposed to be a golfball going into a hole. I've tried to implement the gluLookAt function but it produces a blank screen and I have no idea what I'm doing wrong. I'm guessing I'm not using it properly with Projection mode. Any help would be very much appreciated. Thanks.

code here: http://pastebin.com/RqTxNf9U

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## closed as too localized by bummzack, Nicol Bolas, Josh Petrie, Byte56, Jonathan HobbsNov 15 '12 at 1:13

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You're telling gluLookAt to look up into the sky. Check the documentation.

Your screen will be slightly less blank if you look at the ball. Or alternately, almost anywhere that isn't ten meters up in the air, precisely away from where the interesting stuff in the scene might be.

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 He is not looking into the sky. eye is at {0, 2, -3} looking at {0, 0, 10} with an up vector {0, 1, 0}. The up vector is pointing into the sky, not the look at direction. However, looking at the ball is a good advice anyway :) – Maik Semder Nov 13 '12 at 10:59 @MaikSemder Apparently you don't know that there are people who (with good reasons) prefer to use Z as the vertical axis. – snake5 Nov 13 '12 at 11:16 @MaikSemder Whoops, you're right. I hate these functions which just take a list of floats for the different components of unrelated vectors; I always wind up grouping them incorrectly. Regardless, if you change the 10.0 to a 0.0, you can see the ball moving. (I did actually test the fix, before posting my answer) So not looking up into the sky; just off to one side. – Trevor Powell Nov 13 '12 at 11:34 Hehe @Trevor .. yeah endless parameter-lists are painful :) – Maik Semder Nov 13 '12 at 16:19

You are not pointing the camera at the ball. You are looking at `{0, 0, 10}` but the ball's initial position is at `{0, 0.4, 0.8}`. Change the lookat point (param 4-6) to something like `{0, 0, 0}`, so you are looking near the ball, i.e:

``````gluLookAt(
// eye position:
0.0, 2.0, -3.0,
// look at point (this was wrong)
0.0, 0.0, 0.0,
// up-vector
0.0, 1.0, 0.0);
``````

or even better, use the ball's position directly for the lookat point, this will move the camera each frame to point to the ball:

``````gluLookAt(
// eye position:
0.0, 2.0, -3.0,
// look at point, look at the ball each frame
golfball.getpx(), golfball.getpy(), golfball.getpz(),
// up-vector
0.0, 1.0, 0.0);
``````

But for this to work, you have to fix the rendering of the ball's position, remove `startdispz`otherwise you are not redering the ball on the correct position, change it to:

``````    glTranslatef(golfball.getpx(),golfball.getpy(), golfball.getpz());
glutSolidSphere(golfball.getballsize(),20,20);
``````
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