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# Graphics matrices give odd render results

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It doesn't look like a square when it isn't rotated. Have you got the numerator and denominator the right way around when you calculate the aspect ratio?

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Camera c(1, 100, .25*TAU, WINDOW_WIDTH / WINDOW_HEIGHT);

where WINDOW_WIDTH / WINDOW_HEIGHT is the aspect ratio.

with:

const static float WINDOW_WIDTH = 1024;
const static float WINDOW_HEIGHT = 768;


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Have you tried switching them round? Because a square should look square and it doesn't unless the screenshots you posted are stretched.

EDIT: The eyes look round though!

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Well this is strange, if I switch them around and disable the rotation, the image before looks exactly like after.

Earlier (AR = WIDTH/HEIGHT) - no rotation:

Now (AR = HEIGHT/WIDTH) - no rotation:

Edited by assainator

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Are you actually calling Camera::computePerspective? EDIT: You set the perspective matrix to the identity in the construtor and I couldn't see where you call it. Try this

Camera(float near, float far, float fov, float ar) : near(near), far(far), fov(fov), ar(ar), view(Matrix4f::identity()), perspective(Matrix4f::identity()), x(0), y(0), z(0)

{
setLookat(Vector3f(0, 0, 1), Vector3f(0, 1, 0));
computePerspective();
}

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Put a break point at the point where the matrices are finally calculated, and when they are finally used, and see what the values of the actual matrices. If none of the changes affect anything, then the matrices are ultimately not used. The coordinates you use and the location of the quad ultimately is consistent with an identity matrix.

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Are you actually calling Camera::computePerspective?

That fixed it. WHY did I miss that?

EDIT: Do you have any tips for finding these small problems?

EDIT 2: My palm is inseparable from my face...

Edited by assainator

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Brother Bob gave some good tips.

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My advice kind of assume that you know the projection matrix is wrong to begin with. If you don't know that, you don't really know what to look for in the first place.

But, my advice still stands in a more general form; you need to take advantage of the debugger. You are experiencing problems with the viewing, so use the debugger to inspect everything that has anything to do with getting something onto the screen. Break into the debugger when the values are calculated, and ensure that they are exactly as you expect, or even just reasonable. This requires knowledge of linear algebra and experience to actually know what a "reasonable" value is though, and comes with time.

And what if you finally find out that the projection matrix is not as expected? Go back and figure out where the projection matrix is calculated. This would have been a dead give-away; the debugger would not have reached the computePerspective function if it wasn't called.

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Another tip to do with aspect ratios is changing them when you write and test the function so you can verify the code works. You don't want the width and height to be const anyway, assuming the window can be resized.

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