# Tag Info

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### Why are quads used in filmmaking and triangle in gaming?

For 3D modeling, the usual reason to prefer quads is that subdivision surface algorithms work better with themâ€”if your mesh is getting subdivided, triangles can cause problems in the curvature of the ...
• 2,222

### How to achieve gimbal lock with Euler angles?

A gimbal is a pivoted support that allows you to rotate around one axis. Now it so happens that Euler rotations* work like a set of 3 gimbals attached to each other,...
• 8,437
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### What's the difference between orthographic and perspective projection?

Orthographic projections are parallel projections. Each line that is originally parallel will be parallel after this transformation. The orthographic projection can be represented by a affine ...
• 8,437
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### How to achieve gimbal lock with Euler angles?

Rotations in 3D are normally done with matrices. The xyz Euler angles can be converted to matrices so that it can be used in the rotation. That is where something called rotation order comes in. ...
• 1,605

### Why are quads used in filmmaking and triangle in gaming?

As @Noah Witherspoon correctly, says triangle subdivision does not work as well as quad subdivision. Although, in the beginning triangles could not be subdivided at all. However, he does not really ...
• 8,437
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### Why do I need to inverse the orientation matrix of a camera to be able to translate it in the direction it is facing?

People always forget that there is no "camera" in OpenGL. In order to simulate a camera you have to move the whole world inversely. So if you want ur camera looking 30 degrees downward, you move the ...
• 2,468
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### Is my perspective math correct?

Identifying your axes in both figures and adding the camera position to your first figure would help you understand what's going on. You could also have a single variables for all your points, ...
• 371

### What is the use of homogenous divide?

First of all we need to understand why do we need 4x4 matrices in the first place. With 3x3, we couldn't represent translation as it wasn't a linear transformation (it displaces the origin). So in ...
• 2,468
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### What's the difference between Clipping and Culling?

When it comes to graphics, the term "culling" by itself doesn't really have a single definition or location within the pipeline. The term is sometimes applied to primitives and it is sometimes applied ...
• 9,842

### How to build a 3d model from 2d pictures

This is a bit different from a conventional photogrammetry problem. You're not trying to estimate a 3D world from 2D projections. You have actual 3D information - you have the imaging slices - and you ...

### What is missing in this image that stops it from looking like a photograph?

The hair seems to have sampling noise or aliasing in it. This might be poor jpeg compression but it does not look like it. I've never seen hair part that way (could just be me). The neck looks a ...
• 1,585
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### Minimum requirements to uniquely represent a 3D object in space

A rigid body has 6 degrees of freedom, in 3D- space. So that means you need 6 values to represent the object. The common way to do this is to store a position vector for position and 3 rotations. But ...
• 8,437

### Was Evans & Sutherland CT5 really created in 1981?

The CT5 was designed before 1981. I started working at E&S in May 1981. The CT5 was fully designed by then and 3 had been built. All 3 were still at E&S and hadn't shipped yet when I started. ...
• 61
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### How do graphic engine developers debug their 3D graphics code?

I'm programming mostly in OpenGL. In this case, the very first thing I do is setting up KHR_debug extension. It provides a way to subscribe to messages generated by GL drivers - from errors to ...
• 237

### Generate mesh from pointcloud data

one popular Real time surface reconstruction method is TSDF (Truncated Signed Distance Function) used by Microsoft for the Kinect. It is based on the VRIP method but it is faster. It is based on depth ...
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### Could some give an explanation or hint about this kind of equation? $\left(- \sqrt{X^{2} + Y^{2}} + 1\right) \cos{\left (2 \pi X + \phi \right )}$

The R part generates a cone where the point is at (0, 0, 1) and it spreads out below that. It meets the x-y plane at the unit circle: The ...
• 3,421
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### How to decide which way to triangulate a quad?

A simple heuristic that many 3D content creation apps use is to split along the shorter of the two diagonals of the quad. This generally seems to work pretty well. It minimizes the appearance of long, ...
• 25.1k

### Improved Laplacian smoothing of noisy surface meshes

This is a quite common property of smoothing in 3D. When you have some data and you smooth it out you get some kind of average of the local variation. And this works fine, and stably, in one ...
• 8,437
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### What if we don't mention Modelview and projection matrix?

Your screen isn't 3D, so how do you display 3D objects on it? You need to map 3D coordinates into 2D space. This also explains why your OpenGL code is not behaving how you're expecting it to. Sorry if ...
• 1,353
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### Background behind 3D model

Normally if you paint a background image you simply draw a textured full-screen square while depth testing and writing is disabled before drawing the actual scene (where you re-enable depth) In the ...
• 5,950
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### 3D rotation matrix around vector

There is a direct formula for the rotation matrix for an arbitrary axis and angle. Given a unit vector $a = (a_x, a_y, a_z)$ and angle $\theta$, the matrix can be constructed as follows (derivation ...
• 25.1k
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### How does a rigged model work?

The magic is that the mesh is attached to the skeleton. In it's simplest form, this is done by assigning each vertex to a bone. When a vertex is assigned to a bone, that means that it will always ...
• 7,801

### How to use multithreading in 3D software renderer to speed up fetching texture values

It could be that you have to overcome a different bottleneck first. Have you ever read Jim Blinn's "The Truth About Texture Mapping"? (I had a quick search to see if I could find a non-paywalled ...
• 4,306

### why is translating in 3D space the same as shearing in 4D space?

In a linear transformation system, your origin is always a fixed point, since 0*anything = 0. So imagine you have a cinema screen, and the origin is at the centre of the screen. Using linear ...
• 2,402
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### How did the hard, accurate shadows, work in early 3d (2000 - 2004) games?

Having not worked on these games, I can only speculate... but from your description, it sounds like a crude shadow map with orthogonal projection and no depth information. It probably has (or had) a ...
• 1,585
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### Vulkan: efficient way to update VBO mesh vertices?

With OpenGL I would have to reload whole vertex VBO's. No you wouldn't. You can use glBufferSubData I suppose with Vulkan there could be a way to directly ...
• 521
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### What are the i,j,k components of a 3d mesh on plot.ly (online)?

Most mesh drawing tools use triangles to draw meshes, for technical reasons. You could simply specify the coordinates of the three vertices of each triangle, but that is a bit wasteful in terms of ...
• 216