# Tag Info

24

World coordinates are at the bedrock of your game world. The 3D positions of all objects are ultimately specified in world space, either directly or through a node hierarchy. The ground, buildings, trees, and other stationary things will be fixed in world space. Gameplay calculations and physics will be done in world space (perhaps with some local ...

23

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 assumption that its faster is a bit flawed. Even if it would be faster, it would be less efficient in terms of development (like 1% speed increase for 10 times the ...

21

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 resulting surface. For an example, take a look at these two boxes: The left one is all quads; the right one has the same overall shape, but one corner is made ...

16

Smooth in this case just makes the surface normals at vertices point the same way, when interpolated it looks smooth. Meshsmooth would add vertices. 1) how is the smoothing possible without increasing the detailing of the mesh geometry? Human eyes cant actually see curvature except on the edges of objects. All they can do is approximate the smoothness and ...

15

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 all hardware, because the hardware wasn't doing much. A graphical accelerator allows the drawing of pixels considerably faster than a CPU can, by using ...

14

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 fragment shader. This was all done in software in the 90's when your video card wasn't much more than a blitter and a frame buffer, but it was slow as hell. Hence ...

13

Your image definitely does not look correct, and it appears that you are not correctly computing the internal path of light rays as they travel through your mesh. From the looks of it, I would say that you are computing the distance between the point where the view ray first enters the cube and where it first hits the interior wall, and using that as your ...

9

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, one rotation builds upon the next (or previous/whole stack if your inclined to model it that way). Image 1: Rotation is like a gimbal. Model using yxz rotation (z=blue, x= red and y=green) in ...

8

When talking about file formats, we are talking about persisting some data related to a 3D model/geometry. There is no universal standard on file formats for persisting 3D geometry. There are only a few formats more dominant than others. Just as it is with image file formats, the PNGs and JPEGs are the most common formats out there today, but there is no ...

8

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, generating a 2D matrix with the rows as each point and columns as the components $x$, $y$ and $z$. That way, you could handle the projection using a simple matrix ...

8

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 the box can cut off one corner of the polygon, replacing one vertex with two. So 3 vertices + 6 added vertices due to clipping = 9 total.

8

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 transformation. In contrast a perspective projection is not a parallel projection and originally parallel lines will no longer be parallel after this operation. Thus ...

8

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. Basically it says in what order you rotate the object. First you rotate the object around the x axis, then the y axis and lastly the z axis for example. This means ...

8

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 explain why that is the case. Which is useful information and explains why quads are preferred and how to use them. First, observe that a triangle does gets ...

8

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 order to avoid extra work, homogeneous coordinates and affine transformation was introduced. Now instead of doing $v' = Lv + t$ where L is a linear transform ...

7

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 looks like this: The spheres become circles with the center points $C_1$ and $C_2$, and the intersection circle is now only 2 points with only the closer one $P$ ...

7

Scratchapixel has a nice tutorial on writing a basic rasterizer here. Also, you could use the projection algorithm here to get the position of the vertices in screen space, then use Bresenham's algorithm or DDA to draw lines in between. If you want to fill them too you can use scanline (you can find it on Wikipedia). For ellipsoids, you can either just turn ...

6

Having the horizon fall off is simply dropping the ground in the distance down somewhat. A point $x$ km away if you follow the curve of the planet will be $r-r\cdot \cos \frac{x}{r}$ down and $r\cdot \sin \frac{x}{r}$ out horizontally where $r$ is the radius of the planet you are modeling (~6.3k km for earth). In the vertex shader you can account for that ...

6

In traditional stereo 3D, I don't believe that there is a way to make a fixed focal plane feel natural to the viewer. When looking at an out-of-focus object in stereo 3D, the object remains out-of-focus, causing conflicting cues. The lens in the eye tries to adjust to bring the object into focus, but of course it won't succeed, causing eye strain and ...

6

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 to see if the face was looking towards or away from the view point. My erroneous step was that I was doing this AFTER transforming from world-space to view-...

6

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 renderer but at least one is a standard. So you might be looking for something like: RIB, Renderman Bytestream although it comes with as a programming api as well. ...

6

A standard technique is to use a ray/sphere intersection test inside a pixel shader. One draws a billboard large enough cover the area the sphere could appear on the screen (or drawing a bounding cube) to reduce the number of wasted intersection tests (other geometric shapes could be used). The fragment is killed if the intersection test fails; if an ...

6

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 want to assemble them into a 3D model. That's a much easier problem, the kind you can solve from the comfort of your couch. Do know the cutting planes that ...

6

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 little too regular (I'm no modeler though). The skin's subsurface scattering falls a bit short. Perhaps it's not that but there is something slightly off about the ...

6

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 for obvious reasons any 6 variables that are independent of each other would do this. The problem with vectors is that they aren't the most efficient way to ...

6

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 whole world 30 degrees upwards. If you want your camera moved to the left, you move the whole world right. That's why you will notice the "-" sign in the ...

6

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 maps from different (known) camera positions. you can read more: https://cs.nyu.edu/courses/fall12/CSCI-GA.2945-001/dl/jiakai-slides.pdf file:///C:/Users/...

6

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 cos component defines an extruded cosine wave along the X-axis: So the final equation takes the cosine wave and multiplies its amplitude by the cone. It will have full amplitude at the origin, and decrease to 0 at the ...

5

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' by Yasutaka Furukawa and Carlos Hernández. So to paraphrase: We have a set of images that is larger than two, and use them in a pairwise manner by applying ...

5

Before we begin, let us differentiate between two things: The shape of a sphere, and the topology of a sphere. A NURBS surface can make the shape of a sphere. In a typical configuration, it will be 'open' at the poles. That is the mathematical function of the surface does not wrap over the pole in that it is not a true sphere (it has the shape of a sphere)....

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