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# Camera Zooming In and Out

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### #1Medo3337  Members   -  Reputation: 891

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Posted 05 January 2013 - 12:36 PM

I thought zooming in can be accomplished by moving the camera forward but unfortunately it doesn't work like that.

Lets say I want to zoom in for a sniper sight, moving the camera forward will cause a problem if there is something close, for example: A close wall.

How do I create a method like: Camera::Zoom(float amount); ?

### #2phantom  Members   -  Reputation: 10562

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Posted 05 January 2013 - 12:44 PM

To get a zoom effect you can adjust the field of view used in your projection matrix calculation.

### #3Medo3337  Members   -  Reputation: 891

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Posted 05 January 2013 - 02:51 PM

I have the field of view set to "D3DX_PI / 4" by default, how do I change it to add zoom in/out amount so when I call the method Zoom(float amount); I can change the field of view accordingly?

I tried:

camera->fov = (D3DX_PI / 4) + amount;

Not sure if the above is correct, however it cause a problem when amount reach certain number, the camera get up side down.

### #4NewDisplayName  Members   -  Reputation: 359

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Posted 05 January 2013 - 03:16 PM

Your FOV is exceeding pi radians and that's why you see inverted images after some amount. It's based on the principles of focal point in optical physics.

Edited by NewDisplayName, 05 January 2013 - 03:18 PM.

### #5Paradigm Shifter  Crossbones+   -  Reputation: 5832

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Posted 05 January 2013 - 03:22 PM

You want to multiply the field of view by a float between 0 and 1 to zoom in. Use 1 for normal zoom, experiment for the zoomed in value. You can interpolate the zoom amount to zoom in smoothly. Try 0.5 to start with (should make everything twice the size) and tweak from there.

camera->fov = (D3DX_PI / 4) * amount; // amount = 1.0f -> no zoom
"Most people think, great God will come from the sky, take away everything, and make everybody feel high" - Bob Marley

### #6Medo3337  Members   -  Reputation: 891

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Posted 07 January 2013 - 12:00 AM

@Paradigm Shifter: What If I want to zoom in more?

Also, I notice two problems when I zoom in till the maximum value:

1. The textures get weird effect

2. The camera can see what is the behind the mesh (like it's penetrating the mesh) which is not realistic.

### #7Hodgman  Moderators   -  Reputation: 48915

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Posted 07 January 2013 - 12:22 AM

Don't treat "D3DX_PI / 4" as some kind of magic number -- Pi/4 radians == 45 degrees.

You can work in degrees to make things more obvious if you want to, e.g.

float regularFov = 45.0f;
float sniperFov = 5.0f;
camera->fov = DegreesToRadians( isSniping ? sniperFov : regularFov );

### #8Medo3337  Members   -  Reputation: 891

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Posted 07 January 2013 - 12:55 AM

@Hodgman: When zooming, the value shouldn't change suddenly, instead, the zoom should be changing smoothly.

I have the same problems that I mentioned when earlier when I zoom in to the maximum value, I also want to zoom MORE than the maximum value.

### #9Hodgman  Moderators   -  Reputation: 48915

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Posted 07 January 2013 - 01:15 AM

It was just an example of using intuitive values in degrees, you can animate them however you like, e.g.

inline float lerp( float a, float b, float f ) { return b*f + a*(1-f); }
float fovDegrees = lerp( regularFov, sniperFov, zoomFraction )

What is your maximum zoom value -- what fov value are you using as the 'maximum'? If you use an fov of 0, then you'd end up with an infinitely thin frustum with no area... but any value greater than 0 should work (and smaller than 180º...)

Can you post a picture of your "weird" textures?

Edited by Hodgman, 07 January 2013 - 01:16 AM.

### #10NewDisplayName  Members   -  Reputation: 359

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Posted 07 January 2013 - 02:14 AM

when I zoom in to the maximum value, I also want to zoom MORE than the maximum value

Only way you can achieve this is to set your "maximum" value as some value, which is slightly short of the absolute maximum value (pi radian).

### #11Evil Steve  Members   -  Reputation: 2012

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Posted 08 January 2013 - 12:52 PM

Don't you want to decrease the FOV to zoom in, rather than increase it?

Steve Macpherson
Senior Systems Programmer

Rockstar North

### #12Burnt_Fyr  Members   -  Reputation: 1621

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Posted 08 January 2013 - 01:05 PM

As Steve curiously asked, a small FOV should result in more zoom(And by asking, I'm sure it was more a question you should ask yourself). As Hodgman noted, a FOV of 0 results in just that. 0 field of view, your frustum essentially becomes a 2d slice(whose angle would depend on the aspect ratio), rather than a volume. A FOV = epsilon is the maximum zoom you could possibly get.

Sidenote: Hodgman, you asked if we could see the "weird textures" I'm guessing here, but are you expecting a moiré pattern?

Edited by Burnt_Fyr, 08 January 2013 - 01:10 PM.

### #13Medo3337  Members   -  Reputation: 891

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Posted 08 January 2013 - 04:15 PM

@Burnt_Fyr: Exactly, when I zoom in sometimes I see a slight moiré pattern which make the texture looks weird.

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