# Tagged Questions

Transformation in game development is usually refers to linear algebra operations on points, vectors and matrices.

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### Why do we move the world instead of the camera?

I heard that in an OpenGL game what we do to let the player move is not to move the camera but to move the whole world around. For example here is an extract of this tutorial: OpenGL View matrix ...
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### Rotate object to always face camera

I'm trying to make a TextMesh appear when ever an enemy prefab is hit. I currently have this functionality working. However, the text doesn't face the direction the players camera is looking. At the ...
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### Inverting matrix then decomposing gives different quaternion than decomposing then inverting the quat

I'm getting different signs when I convert a matrix to quaternion and invert that, versus when I invert a matrix and then get the quaternion from it: Quaternion a = Quaternion.Invert(getRotation(m)); ...
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### getting bone base and tip positions from a transform matrix?

I need this for a Blender3d script, but you don't really need to know Blender to answer this. I need to get bone head and tip positions from a transform matrix read from a file. The position of base ...
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### Keep Mini map static after rotating / zooming with camera

Hi I am making a 2D game, where the Camera is able to rotate / zoom in or out on the camera focus (the player usually). However my game also contains a mini-map, and so far whenever I have to rotate ...
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### Why do we need a fourth coordinate to divide by z?

I read the response here: What does the graphics card do with the fourth element of a vector as the final position? "The fourth component is a trick to keep track of perspective projection. ...
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### How can I attach a model to the bone of another model?

I am trying to attach one animated model to one of the bones of another animated model in an XNA game. I've found a few questions/forum posts/articles online which explain how to attach a weapon ...
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### importing animations in Blender, weird rotations/locations

This is for the Blender 2.6 API. There are two problems: 1. When I import a single animation frame from my animation file to Blender, all bones look fine. But when I import multiple (all of the ...
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### Translate along local axis

I have an object with a position matrix and a rotation matrix (derived from a quaternion, but I digress). I'm able to translate this object along world-relative vectors, but I'm trying to figure out ...
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### Transformation matrix that maps a window

I'm currently learning OpenGL at uni, and they give us questions to help us learn (these are not worth anything), however I'm stuck on this one question and would have to travel over an hour and a ...
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### Transform 3d viewport vector to 2d vector

I am playing around with 3d transformations and came along an issue. I have a 3d vector already within the viewport and need to transform it to a 2d vector. (let's say my screen is 10x10) Does that ...
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### Do matrix manipulations for 3D graphics ever produce singular matrices?

A singular matrix is a matrix that cannot be inverted. The vecmath library, for example, throws a SingularMatrixException if you try to invert a singular matrix. I think I understand what singular ...
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### what is the very last element of a 4x4 transformation matrix for? [duplicate]

while its a similar value to its neighbour - Z translation (and I wont say if thats above or to the left for fear of sparking a religious war!) and it only seems to change when the Z translation value ...
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### Bullet Physic: Transform body after adding

I would like to transform a rigidbody after adding it to the btDiscreteDynamicsWorld. When I use the CF_KINEMATIC_OBJECT flag I am able to transform it but it's static (no collision response/gravity). ...
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### How to compute a transformation matrix that describes each position and rotation on a sphere?

I am having an issue constructing my transformation matrices, for this sphere problem. I know the 3d coordinate of the center, and the radius of, the sphere. Since I know the radius and center ...
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### Translating local to global coordinates in ARToolkit / OpenGL

Ok, so I've tried reading over the other questions and something's just not clicking for me. I am working on an augmented reality application using ARToolkit, however it should just be straight ...