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28 votes
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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 them—if your mesh is getting subdivided, triangles can cause problems in the curvature of the ...
Noah Witherspoon's user avatar
23 votes
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Why do we have graphics frameworks like OpenGL and DirectX, when games could just draw pixels directly?

Speed is the most common reason why this is not done. In fact you can do what you propose, if you make your own operating system, its just going to be very slow for architectural reasons. So the ...
joojaa's user avatar
  • 8,407
14 votes

Why do we have graphics frameworks like OpenGL and DirectX, when games could just draw pixels directly?

work on any 32-bit color GPU (even old ones)? Bit of history here: this is how games were done on PC up until graphical accelerators started to become available in the mid-90s. It did indeed work on ...
pjc50's user avatar
  • 241
14 votes

Why do we have graphics frameworks like OpenGL and DirectX, when games could just draw pixels directly?

Just to add to joojaa's answer, things are still being drawn pixel by pixel. You're just generating the pixels using a vertex shader/assembler/rasterizer, then texturing and lighting them using a ...
russ's user avatar
  • 2,382
13 votes

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,...
joojaa's user avatar
  • 8,407
11 votes
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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 ...
joojaa's user avatar
  • 8,407
11 votes
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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. ...
bram0101's user avatar
  • 1,595
9 votes
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Maximum number of vertices after clipping a triangle against an AABB

Funnily enough, I asked this exact question on Math.SE a couple years ago: Maximum number of vertices in intersection of triangle with box. The answer is 9 vertices, because each of the 6 planes of ...
Nathan Reed's user avatar
9 votes

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 ...
joojaa's user avatar
  • 8,407
7 votes
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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, ...
Soravux's user avatar
  • 371
7 votes
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Sphere intersection occlusion (for hybrid raytracing)

Given that I didn't miss anything, you can probably cut this down to a problem in the 2D space. Viewing onto the plane defined by the center points of the spheres and your camera origin, the scene ...
Nero's user avatar
  • 1,320
7 votes
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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 ...
gallickgunner's user avatar
7 votes

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 ...
gallickgunner's user avatar
6 votes
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Graphics Pipeline: Viewspace & Back face culling incorrectly

I (believe) I've solved this (even if it has taken 2 days). My problem was essentially I wanted to take the dot product of the face normal, and line-of-sight vector like below And determine the angle ...
davidhood2's user avatar
6 votes

Human Readable/Writable 3D Representation Formats/Languages?

There are a number of formats that might fit the bill. Depends on what you want to achieve. Most likely your looking for a scene description language for renderers. Many of them are for that one ...
joojaa's user avatar
  • 8,407
6 votes

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 ...
Jacob Panikulam's user avatar
6 votes

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 ...
Olivier's user avatar
  • 1,585
6 votes
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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 ...
joojaa's user avatar
  • 8,407
6 votes

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. ...
John's user avatar
  • 61
6 votes
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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 ...
joe_chip's user avatar
  • 237
6 votes

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 ...
ChaimDryzun's user avatar
6 votes
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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 ...
Nicol Bolas's user avatar
  • 9,752
6 votes
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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 ...
user1118321's user avatar
  • 3,401
6 votes
Accepted

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, ...
Nathan Reed's user avatar
5 votes
Accepted

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 ...
Nathan Reed's user avatar
5 votes
Accepted

What is stereo about multi-view stereo?

Multi-view stereo (MVS) is the general term given to a group of techniques that use stereo correspondence as their main cue and use more than two images. A quote from 'Multi-View Stereo: A Tutorial' ...
Dragonseel's user avatar
  • 1,810
5 votes
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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 ...
ratchet freak's user avatar
5 votes
Accepted

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 ...
aces's user avatar
  • 1,353
5 votes

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 ...
joojaa's user avatar
  • 8,407

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