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# Questions tagged [matrix]

A 2D array of numbers, symbols or expressions, arranged in rows and columns. Each row must have the same number of columns. The numbers, symbols or expressions themselves are called elements or entries.

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### Tetris: 2D Rotation Matrix?

I'm creating a Tetris clone right now. I've got the tiles of tetromino stored as an std::array<tile, 4>. Each ...
1k views

### Matrix transform from one coordinate system to another

I have been beating my head against the wall for weeks on this and it is time I just break down and ask for help. I need to move a 3D camera from an in house system into Unreal 4. The two use ...
124 views

### Is it normal in skeletal animation to NOT consider the translation component in bone transform matrices?

I'm using assimp to load a model, and DirectX11 and DirectX ToolKit to render it. In the document of DirectXTK's IEffectSkinning, it says: As an optimization, SkinnedEffect and DGSLEffect assume ...
187 views

### Rotating a 4D matrix about the Y axis with an X-Z vector

I should mention that I'm pretty new to Matrices and will probably need a layman's answer to my question. I have a 4D matrix which represents the rotation of an object in 3D space. I have a ...
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### How much to roll Z to make horizon level

I've got a flying camera with some arbitrary rotation. (It also has a translation, but that's not important.) It's flying along its local Z axis, traveling in some direction over the ground with some ...
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### How to transform a matrix's local space position into another's local space

When looking at an example to learn how to do per pixel collision, I came across this: ...
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### Why would this scaling matrix have no effect?

To draw a simple model using the DirectXTk, I'm doing the following. It all works perfectly, draws correct, and so on. Except changing the scaling factor makes NO difference, and I can't figure out ...
470 views

### Using glm to rotate the modelview matrix based on the cursor position

I am rendering a 3D model of an object, and I want the user to be able to rotate around that object by dragging the mouse. To do this, I want to use the cursor position to continually update the ...
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my function: ...
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### XNA 2D rotation Matrix offset/origin

I'm currently struggling with finding the offset for my original camera translation after I have applied a rotation for it. ...
440 views

### opengl matrix multiplication

Can someone provide some type of example of multiplying a 4x4 matrix without using loops? typedef struct matrix4 { data[16]; } m4; can someone provide a ...
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### Camera (pole cam) implementation problem

In my project I have simple scene graph to render whole scene and Bullet physics SDK to provide physics simulation. Each rendered object is represented as scene node. Camera always has target and ...
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### Does converting quaternion to matrix cause a lot of overhead?

This is related to rendering creating a model, view, projection matrix for opengl. While matrix are fairly standard there's a lot of talk about using quaternions for rotations but why would u go from ...
534 views

### How to calculate if a point is contained in rectangular camera viewport with rotation?

I am working with my camera, and am trying to improve it so that I can calculate if a world point is on screen, taking rotation into account. Currently, my camera rectangle is calculated as so: ...
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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. When ...
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### How to understand kind of matrix/world from implemented math operations?

i'm a newbie in 3d programming, and i approach for the first time this argument. I try to make some changes to an existing 3d object viewer, to better suite my needs. This object viewer is jsc3d. I ...
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### 16-byte aligned matrix in DirectX9 and D3DX with Havok Physics 2012

I want to ask a question about D3DXMATRIX and D3DXMATRIXA16, and how to use them with Havok Physics. I'm using Visual Studio ...
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### How can I keep the clicked point under the mouse when rotating? (GLM)

I have a spherical mesh of radius 1, centered at (0,0,0) in world coordinates. I want to rotate the sphere so that the clicked point remains under the mouse at all times. However, I cannot find an ...
96 views

### Rotate an objects velocity

I have a collision system (in 3D but for the purpose of the question assume 2D) where I want to calculate the new velocity (stored as a vector) after a collision. What I have is the velocity of the ...
122 views

### Problems Animating Texture in OpenGL

I'm trying to animate a texture to scroll a static screen for a television, however I'm having some issues. Just translating within the texture matrix animates all textures in the scene which is ...
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### How can I calculate the orthographic projection needed to encompass an object with arbitrary rotation?

So I need to set up the dimensions of a orthographic projection that will encompass the entirety of a bounding box when viewed from any arbitrary position. That's an eye (programmer art); and the ...
299 views

### how to stop camera at the end of world map when zoomed in

Im building a tile-based game, and Im trying to implement zooming in on the center of the screen. My problem is, when I get to the edge of the map and im zoomed in, Im noticing that my camera doesn't ...
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### OpenGL: Is it efficient ok to glPushMatrix, plMultMatrix, plPopMatrix for every object in my scene?

I'm very new to opengl, and I might not fully understand the openGL matrix projection stack thing. So, I have about 300 'objects' in my scene, each with their own position/rotation, and I want to ...
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### Problems with Rotation Matrices on Certain Axes

Here is what my rotation matrix looks like: ...
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### Confused About My Code Suggesting The Normal Matrix Is Equivalent To The ModelView Matrix

I'm learning environment mapping in OpenGL by following this page. In his vertex shader, the author calculates the vertex normal in eye space with the following code: ...
742 views

### Java OpenGL Perspective matrix not working

I'm trying to render a simple triangle with OpenGL in Java using LWJGL3. Everything is working great, but the projection matrix (perspective) is not working. In C++ I just used to apply the ...
895 views

### change position/orientation of a bone using assimp

I have been using assimp to import rigged models and animations. I followed this tutorial for skeletal animation and I have got it done properly. The part that I am trying to do now is to orient a ...
51 views

### Matrix Rotation Only Works On one Axis At A Time

I have this function in my vertex shader. It makes a transformation matix out of a transformation matrix, a rotation and an intensity. It works just fine when setting the rotation of one of the axis (...
254 views

### Pre-calculating skeletal animation data

I'm working on skeletal animation and so far I've got the skeleton drawn with interpolated animation working (just on the cpu still). I was thinking about changing my file format for my skeleton and ...
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### Rotate object around fixed axis

I am trying to let the user of my app rotate a 3D object drawn in the center of the screen by dragging their finger on screen. A horizontal movement on screen means rotation around a fixed Y axis, and ...
563 views

### Pre- or post-multiplication for rotation between coordinate frames

I have three 3D coordinate frames: O, A and B, as shown below. I want to know the rotation matrix RAB between A and B, that is the rotation that is required, with respect to the frame A, to move from ...
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### Inline-Building a World (SRT) Matrix

Currently, to construct a world matrix, I have the following code: return FromScale(scale) * rotation.RotMatrix * FromTranslation(translation); However, this is ...
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### Why do we refer to a “model view” matrix and not a “viewprojection” matrix?

Why there is a model-view matrix, but not a view-projection matrix? A view-projection matrix would make much more sense to me, since every entity in the scene has his own position and therefore its ...
136 views

### Rotate heading relative to agent's local space

I'm having a little trouble translating a point in my game's world space to an object's local space. I have a cannon in my game with a normalized heading vector that's always supposed to point in the ...
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### Project rotated matrix to isometric coordinate

I have a group of soldiers, and each has a vector describing their position in the squad. When the group rotates, I do this math to calculate the desired position of each soldier. ...
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### libgdx - Box2d debug draw not correct

I have a problem where the bodies in my debug draw does not draw correctly, take a look: As you can see, there is some space between the dynamic body and the ground. I have checked the contact ...
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### Binding an Instance Matrix with an InputLayout

If I want to bind an instance matrix to a vertex shader, how do I go about it? For example, here is a super-simple VS input: ...
258 views

### How to position a Weapons model in a first person shooter with XNA

I am building a first person shooter and positioning the weapons is hard. I am trying to get the bat to look like you are holding it but I keep trying things and they don't appear in the positions I ...
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### Scaling world - projection, view or separate matrix?

I am currently writing a simple 3D space visualisation program. Things get loaded into it from a simple XML file, which contains positions and sizes of objects in space, so you can put basically any ...
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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 ...
382 views

### What is FOVx in this diagram?

a beginner game developer here. I have recently taken upon learning about 3D game development and I am stuck on a simple matrix problem. The image is found from this article: http://www.codinglabs....
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### Connecting a model's joint to the joint of another model

I am trying to figure out the math behind orientating and translating a model so that a specified point on the model will connect with a specified point on another model. For example, given the ...
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### OpenGL light appears to move with camera and changes with object rotation

I have a working open gl es 2.0 3d engine (my own) that I've used in several iOS apps. I recently noticed that on a mutli-symmetrical object the lighting didn't look the same at each rotation. For ...
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### How can I reverse the effect of a transformation matrix?

I have recently been working on a game with using OpenGL and C++ through GLFW. In the game I have an airship with a turret mounted on it. The airship moves around in world space coordinates and the ...
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### Transformations and basis vectors

I've been reading this very nice tutorial on OpenGL, and I encountered a statement which I can't wrap my head around. In Chapter 6, it states: Transformation from one space to another ultimately ...
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### Problematic cameraposition (Eye = (0,0,0), at=(0,-2,0) and up = (0,1,0))?

I am taking a course in computergraphics and we talk a lot about OpenGL and the math you need to do everything OpenGL does "by hand". A Question which was asked in an old exam (I am preparing at the ...
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### 2D HLSL World position

I'm trying to get world position from my vertex shader to my pixel shader so that I can disable the shader once a preset X coordinate has been passed (no shading once I'm over X). Getting the screen ...
376 views

### Directional lights (not) rotating with camera (opposite problem)

I am trying to implement a shader for directional lights correctly, but I am bit confused as to why it works when it shouldn't and vice versa. People usually encounter problem with lights changing ...