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# Aspect ratio with rotation issues

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7 replies to this topic

### #1XNobodyX  Members

Posted 02 February 2014 - 12:09 PM

I have been playing around with directX and I ran into a problem with squares not being squares if the window wasn't a square. I eventually realized this was because I was not implementing an aspect ratio. I thought I had fixed this problem until I added rotation.

When I rotate my squares they become distorted, the angles are no longer 90 degrees

This seems like it is yet another issue with aspect ration that I do not know how to fix. Any help would be greatly appreciated.

No rotation:

Rotation:

Starting at top left going to bottom right, 10 degrees, 90 degrees, 30 degrees

Rotation with square window:

Starting at top left going to bottom right, 10 degrees, 90 degrees, 30 degrees

### #2Buckeye  GDNet+

Posted 02 February 2014 - 12:55 PM

Couple things:

Do you reset the aspect ratio every frame you render (for instance, after a window resize)?

Is the eye position the same in each picture you posted? What is the position and direction of the view?

Is the projection perspective or orthographic?

What axis are you rotating the square around? A square will, indeed, appear as a rhomboid, depending on the direction from which it's viewed.

To complement question on the rotation axes for the squares, how are your world axes arranged in the pictures you posted?

Edited by Buckeye, 02 February 2014 - 01:00 PM.

Please don't PM me with questions. Post them in the forums for everyone's benefit, and I can embarrass myself publicly.

You don't forget how to play when you grow old; you grow old when you forget how to play.

### #3XNobodyX  Members

Posted 02 February 2014 - 01:46 PM

Do you reset the aspect ratio every frame you render (for instance, after a window resize)?

Only once so far. When I show the different sizes above I just change the window size and re-run

Is the eye position the same in each picture you posted? What is the position and direction of the view?

Yes, It is in the same place

Is the projection perspective or orthographic?

Ortho

What axis are you rotating the square around? A square will, indeed, appear as a rhomboid, depending on the direction from which it's viewed.

Rotating around the center of the squares

To complement question on the rotation axes for the squares, how are your world axes arranged in the pictures you posted?

X left and right, Y Up and down, Z front back

### #4Buckeye  GDNet+

Posted 02 February 2014 - 09:07 PM

Just noticed you're working with Dx11 (with which I'm not familiar) but that may not matter. However, give us some help here. Try to describe what you're doing in a bit more technical detail. I'm assuming you're in some sort of 3D app (not 2D), correct?

Sorry I didn't think of it before but ... have you tried rendering a sphere? It should appear to be round whatever it's rotation. That will tell you whether the problem is with the aspect ratio or not.

Consider that the problem may or may not be the way you set the aspect ratio. E.g., the problem may be how you rotate and move the squares. Do you apply the rotation with the center of the square at the origin and then move it to position for rendering?

Please don't PM me with questions. Post them in the forums for everyone's benefit, and I can embarrass myself publicly.

You don't forget how to play when you grow old; you grow old when you forget how to play.

### #5Hodgman  Moderators

Posted 02 February 2014 - 10:46 PM

Post the code for setting the aspect ratio.

### #6haegarr  Members

Posted 03 February 2014 - 02:29 AM

There are 3 possible reasons I can think of if the aspect ration is actually the problem:

1.) The projection is not set up correctly, so that the aspect ratio of the view frustum is not equal to the aspect ratio of the window.

2.) The mapping from the normalized co-ordinates to pixels is not correct (in OpenGL the "viewport"; don't know how it is called in D3D).

3.) The rotation matrix is not computed correctly (de-normalized rotations yield in shearing). However, this possibility is less probable because I assume that you use D3D's API routines.

Notice that the aspect ratio of the center rect (the one rotated by 90°) is approx. 2:1, what does not correspondent to the aspect ratio of the window but is even significantly wider. This may hint at your attempt to correct the aspect ratio uses the inverse of the desired ratio.

As others have stated correctly, without a look in the relevant sections of your source code we can just guess what the problem actually is.

### #7XNobodyX  Members

Posted 05 February 2014 - 06:00 PM

Just noticed you're working with Dx11 (with which I'm not familiar) but that may not matter. However, give us some help here. Try to describe what you're doing in a bit more technical detail. I'm assuming you're in some sort of 3D app (not 2D), correct?

Sorry I didn't think of it before but ... have you tried rendering a sphere? It should appear to be round whatever it's rotation. That will tell you whether the problem is with the aspect ratio or not.

Consider that the problem may or may not be the way you set the aspect ratio. E.g., the problem may be how you rotate and move the squares. Do you apply the rotation with the center of the square at the origin and then move it to position for rendering?

Post the code for setting the aspect ratio.

^^

I just take each object's width and divide by the aspect ratio.

tEntity.setWidth(tEntity.getWidth() / (screenWidth / screenHeight));


### #8Hodgman  Moderators

Posted 05 February 2014 - 09:02 PM

I just take each object's width and divide by the aspect ratio.

tEntity.setWidth(tEntity.getWidth() / (screenWidth / screenHeight));

Are those variables floats or ints?

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