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# Questions tagged [algorithm]

Questions about the rigorous usage of instructions used to solve a specific computer graphics problem.

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1 vote
82 views

### Search for special image difference metric

For regression tests of our note typesetting program, LilyPond, we currently use ImageGraphick's compare program with the MAE metric (mean absolute error, average ...
• 111
14 views

### Querying a point to find the tetrahedron it lies inside in 3D

I have a set of non-intersecting packed tetrahedrons in 3D space. What is the most optimized way to find the tetrahedron inside which a query point lies? Edit: I tried some data structures and ...
• 11
1 vote
35 views

### How to get the shortest segment AB between 2 SDF (Signed distance field) in 3D?

Is there a method to find the shortest segment between 2 Signed distance field? I know how to calculate this segment for a limited number of SDF like from sphere to sphere, from capsule to sphere, ...
• 11
1 vote
42 views

### Automating equirectangular horizon detection in 360 images

I would like to programatically identify pitch and roll numbers that will level the horizon on each frame in a series of equirectangular 360 panorama images. Here's why. I recently ended up with a ...
• 111
1 vote
30 views

### How to morph a enclosing mesh according to the enclosed mesh?

I am quite new to meshing and mesh manipulation. I am working on a problem consiting of meshes $A$, $B$, and $C$. The mesh $C$ completely encloses the meshes $A$ and $B$ as shown in the attached ...
• 11
1 vote
49 views

### L-System to generate the Penrose P3 tiling

I am trying to write an L-System to generate the Penrose P3 tiling (with thin and thick rhombi, I will call them Rhombus-A and Rhombus-B. For render, I am planning to use the following chars. '+' ...
• 111
1 vote
149 views

### Constructing half-edges table from triangle list without hash

Motivation I am trying to refine a mesh such that each triangle gets subdivided into 4 triangles, but I want the vertices to be shared. For that purpose I need a half-edge data structure so I can ...
• 2,226
31 views

### Normal blend mode math

I have one question. How to calculate source color after blending operation. For example. I have 1 - Background color (r-115, g-94, b-67, a-1) 2 - Foreground color above background color, which ...
115 views

### Extrapolating geometry across a triangle mesh?

Say you have 2 parametric cylinders represented as triangle meshes with very different geometries and you connect them together. Is there a method that allows you to join them together such that the ...
• 1,746
1 vote
64 views

### Piecewise smoothing of a mesh?

Kobbelt et al. published a paper some 20 years ago where they specified how solving Poisson equations on the positions of a mesh lead to removing noise. This can be used for reconstructing mesh ...
• 1,746
20 views

### How is re projection usually implemented in remeshing?

I was reading "Polygon Mesh Processing" and in chapter 5 the authors present this little algorithm: ...
• 1,746
58 views

### What is a smart way to fill in the 'next' pointer of a opposite half-edge of a boundary?

I was reading this question regarding half edges from 3 years ago and the selected answer seemed pretty smart to me. However, while actually implementing it I'm confused at the part where I have to ...
70 views

### What algorithms are typically used for finding 'PCB Trace'-like paths?

I am analyzing a large amount of Layers 0-4 Network Data. I am trying to render diagrams dynamically showing the Network Devices involved in the data (Desktop, Switch, Router, Server, etc.) and how ...
• 101
59 views

### Why capsule box intersection algorithms not widely used

I have searched through a lot of libraries and sources, that include very diverse intersection algorithms, for computer graphics. And I've never found a capsule-box intersection algorithm. Despite ...
• 516
219 views

### Relative coordinates -- cumulative sum

I have a vertex shader happily producing all the vertices I want for a 2D plot. Now I want to also render a plot of the same data, but each point relative to the previous one, like SVG Paths using <...
• 11
1 vote
45 views

### Are systems like double pendulum used for generating terrain?

Looking at the output of the angle of this double pendulum made me think this was a good candidate for generating realistic looking terrain profiles. I can't be the first to notice this so I was ...
• 83
908 views

### Can you explain to me the Bresenham's line algorithm in simple terms?

I've been trying to wrap my head around this algorithm, and I need it for my drawing function. But I can't seem to understand it. The Wikipedia page gives this piece of code right at the end: ...
• 41
355 views

### How to find the nearest palette color when dithering in RGB

I maintain an image dithering library and command line tool. When I was initially developing the library, I was trying to figure out how to match dithered RGB values (containing quantization error or ...
• 143
253 views

### Algorithms for rendering overlapping (floating) windows in 2D

I'm trying to figure out a solution to a problem that looked simple at first: how to render overlapping windows in a 2D windowing system. Originally I was thinking about implementing a text-based UI ...
1 vote
97 views

### Temporal reprojection of specular reflection - finding previous frame color

In specular reflection result depends on view vector from camera to point. Because of that, when doing temporal reprojection and reprojecting position of current fragment while camera is translating, ...
• 2,169
154 views

### Plot inverse of emulated double-precision floats

I need to accurately plot a line chart using WebGL. The numbers have a precision of around 33 bits - that's too many to fit into a single-precision float's mantissa. WebGL does not support the double-...
• 101
2k views

### How to calculate volume of any given 3D mesh

Given 3D mesh with a closed surface. (solid object without hole). I'm looking for an algorithm to calculate its volume. There are several ideas, Such as Voxelized and count voxels Point cloud and ...
• 143
1 vote
136 views

### Turning colorized comic-art into uncolorized monochrome (line-art-inks-only B&W), not just very-light-grayscale

I'm trying to figure out how to go about removing the "colorization" of comic/cartoon/manga/etc drawn-art inputs where the black-ink strokes ("the line-art") are to be retained ...
• 11
1 vote
47 views

### Algorithm for transforming PNG anti-aliasing to smooth paths

I read the pixels of PNG files via libpng and creates an array of alpha channels (showing visible pixels for a monochromatic image). int pixels[height][width]; <...
• 131
1 vote
140 views

### Extrusion Algorithm For Bezier Curves

I just posted this to SO but the question got closed, so I hope it's OK if I try it again here. They say "we don’t allow questions seeking recommendations for books, tools, software libraries&...
• 127
1 vote
186 views

### What does an algorithm which handles mesh-based image morphing look like?

In recent years, the technology of Live2D has become particularly popular and I have been attempting to find any papers or articles which explain what the mathematics for the mesh-based image morphing ...
523 views

### Having trouble implementing distance transform with jump flood

I'm attempting to use the jump flood algorithm to compute distance transforms of an arbitrary texture derived from a canvas2d context, roughly following the explanations detailed here/here. In the ...
• 23
1 vote
71 views

### How is the beam transmittance calculated in PBRT V3?

In pbrt v3, the book gives this description of beam transmittance, but I don't know how to solve the differential equation like it says to get Tr , can someone please tell me how to solve the ...
57 views

### Efficient method of mapping any RGB tuple onto a list of RGB indices, is using some kind of partition plane viable?

Suppose we want to convert an RGB image into a paletted image. As an example, we may have a 1024x1024 image, and we want to map it onto 512 unique colors. All the colors are RGB. This is a problem of ...
• 101
130 views

### How is raytracing performed in anisotropic media?

I wish to determine the path taken by a light ray between two points, $a$ and $b$, through an anisotropic medium. More specifically, this medium has an index of refraction which varies as an ...
• 123
1 vote
134 views

### wall clock using bresenhams circle drawing algo

I am new to CG and I need to draw a wall clock using bresenhams circle algo . I have drawn a circle using this algo but how do I add minute and hour needle in it basically how do i add lines inside a ...
• 11
61 views

### Fractal dimension of landscape generated with Fournier's midpoint algorithm (recursive subdivision) is 2.0 no matter what. Why?

I am using Fournier's midpoint algorithm (recursive subdivision) to construct a landscape of 1025 x 1025 gridpoints, then I am using an advanced version of box counting to find fractal dimension, D. ...
12k views

### How can I get a signed distance (SDF) from a mesh?

I am trying to use constructive solid geometry (CSG) and boolean operators to combine various shapes and get the outer (possibly concave) hull. This seems to work okay when using primitive shapes like ...
• 41
1 vote
170 views

### getting the outline of an arbitrary set of shape unions

I hope this is the right forum to ask this question. I want to experiment with procedurally generating some buildings, and as a first step I want to generate a 2D shape to use as a foundation for the ...
• 113
300 views

### results of Curved PN-Triangles algorithm has visible edges

I implemented the curved PN triangles algorithm described in this paper to smooth geometry in real time. After the implementation was finished (in glsl) I realized, that this algorithm smooth the ...
• 1,309
43 views

### Is this way of transforming QMC samples into barycentric tri coordinates agnostic to mesh-topology?

While I'll try my best to give all relevant info in all possible brevity below, please refer to the spoiler and link at the bottom of the post for the (more lengthy) original description if needed. ...
55 views

### Divide mesh according to level of detail

Background I need to remesh by OpenVDB, like what Blender remesh does: Voxel Uses an OpenVDB to generate a new manifold mesh from the current geometry while trying to preserve the mesh’s original ...
• 133
107 views

### Existing method to automatically fill in this sort of concavity in meshes?

I am working with a PWP3D-like algorithm that renders silhouettes of a mesh in order to segment a frame of video and update an object's pose. Because it is only the silhouettes of the mesh that matter,...
56 views

### Under what conditions does a mesh operation cause the mesh become non-manifold and how to avoid it?

I'm implementing some mesh operations (e.g. edge collapse, edge split, edge flip etc) and need to ensure applying such operations does not cause the mesh to become non-manifold. However, I'm not sure ...
• 241
43 views

### Differential or intersection of islands of 2D polygons in different layers

I have a 2D layer/section containing the 2D polygons colored in shades of green. I have another layer containing the 2D polygons colored in shades of blue. I intend to figure out how different are ...
• 133
367 views

### Rotate a Bitmap with Shearing

I am rotating a bitmap using the three shear algorithm documented in these articles [1][2]. From about 0-90°, the quality is acceptable, but beyond that it gets progressively more distorted until it's ...
1 vote
2k views

### Rotating a Bitmap

I would like to rotate an bitmap image using math. I have two issues with my current implementation: the pixel-by-pixel rotation of the copied bitmap is extremely slow and it is leaving gaps between ...
1 vote
78 views

### Subdivision scheme where the faces and edges have weights (not necessarily scalar weights)

Subdivision schemes work by considering the vertices and their connectivity information to calculate averaging weights. However, other than specifying which vertices are connected, and perhaps which ...
• 1,746
1 vote
103 views

### Is There an algorithm to remove intersections between two tetrahedrons?

I have a mesh made up of several tetrahedrons, I know for sure that there are intersections between some of them: how can I remove these intersections, without generating others? In other terms: if ...
• 11
119 views

### Rounding a 3D corner with Subdivisions

Following the instructions from this post on Stack Overflow, I have been able to find points A, B, and C from points V1, V2, and V3 and a radius value (code below). I would like to be able to find a ...
1k views

### How do I efficiently calculate the distance to the edge of a shape?

I'm trying to implement something like an "inner glow". That is, I have an image which defines the shape of an object, and then I want to create overlay that is a gradient that goes from the ...
• 131
1 vote
90 views

### How can I pull up the whole area of the square? [closed]

What algorithm can i use to pull entere area? i have this image: are there many algorithms, which algorithm can you recommended me to implement? Edit 1: my square was builded with lines (bresenham), ...
• 121
1 vote
80 views

### How can i stretch a line?

How can I remodel a line, i want to draw first a line then i want to remodel the line such as in paint software, which algorithm should I use? Are there several algorithms to achieve this? i am using ...
• 121
36 views

### How can i use bresemhan to any cases?

i have this bresenham's code, but actually this work only to some cases, how can i complete to any cases? ...
• 121