# All Questions

2,285 questions
5 views

### 3D object to slices like in medical scan

I am novice lacking professional terminology. I want to create from 3D object (let's say from polygon mesh) a slice through to PNG file in order to create something like reverse medical MRI scan. ...
5 views

### Applying perspective divide on x and y only?

In the derivation of perspective matrix, z-value is shifted to w-value so that when perspective divide is applied to the result of matrix-multiplication with position values, the value of z can be ...
11 views

### How to use boolean operations (eg. subtraction) on 3D triangulated objects, originally stored as a .obj file, using openGL or other libraries?

What I would like to do is to create a crater on a field. To do so, I thought that creating a universal crater object (something cone-shaped) and then subtracting it from the field on a specified ...
13 views

### Arrange common items to spell out words

This seems like a pretty easy thing to do, but I've never done anything like it and I would rather not reinvent the wheel - so I'm looking for example code in pretty much any language or an algorithm ...
16 views

### Why did most or all vector graphic devices not support some type of curve input parameters?

In the case of classic plotters, it seems the hardware would have been able to handle (something like bezier) curves with the correct software, but instead curves were drawn very slowly using a large ...
22 views

### How to scale primitive shapes [in Blender] so that they are within a [unit] sphere?

I wonder how is it possible to scale all shapes so that they are within boundaries of a [unit] sphere? I know how to do this for a cube: if radius of the sphere is S...
10 views

I was following this guide for drawing circles using shadertoy. Now I am trying to mimic the examples behaviour in WebGL. Here is a working shadertoy example I try to mimic. The code is not mine, see ...
24 views

### how many watts are in the SPD of the color white?

Please help. I'm trying to implement a ray tracer, going by the PBRT book and got stuck on an issue that I fail to find the answer to. My scenes are made from objects and light sources. From that, I ...
18 views

### Why need a $h$ parameter in the Geometry Function of a BRDF

Geometry Function in the specular BRDF term is defined as $G(l, v, h)$. Why need a $h$ since $h=\frac{l+v}2$. $f_{spec}(l,v) = \frac{F(h,v)G_2(l,v,h)D(h)}{4|n\cdot l||n\cdot v|}$ from "Real Time ...
67 views

### Unfold a 3D mesh to a 2D plane

I'm trying to unfold a 3D mesh onto a 2D plane. My general idea to do this, would be to cycle through all the faces of the meshes and perform a hierarchical transformation. So I would start at the ...
19 views

### GL_DEPTH_CLAMP has no effect (reverse z)

In an effort to improve cascaded shadow maps, I have looked into using GL_DEPTH_CLAMP and moving the near and far plane just around the actual view frustum instead of the global bounding box. But the ...
22 views

### HalfEdge data structure in openmesh, create_face function explanation

Does anyone have experience with open-mesh or computational geometry and can kindly explain what exactly happens in the function below? ...
64 views

### How can I transform an ellipse into a circle?

I have an ellipse which has -45 degree axis. How can I transform the ellipse into a circle? Can I use shear transformation along the x/y axis?
52 views

### 3D coordinates of intersection point in clipping for a rasterizer

When doing clipping in homogeneous coordinates, we need to find the coordinates of the intersection of the viewing frustum with the line to be clipped. This can be done easily if we want those ...
59 views

### Learning light transport using Q-Learning

I am trying to reproduce the results obtained by Dahm et al. in the paper Learning Light Transport the Reinforced Way. This method takes advantage of the similarity between the Bellman equation (Q-...
26 views

### Rendering 3-D point clouds obtained from depth maps as a 2.5D video

Suppose I have code to generate a bunch of frames, each of which is a depth map(I have access to the matrices which represent depth) which in turn is used to generate a point cloud. One frame would ...
90 views

### Why the ray tracing result looks weird?

I followed the book Ray Tracing in One Weekend and implemented a simple ray tracing procedure. There are 100 random samples every pixel for antialiasing, but the render result looks weird: There is a ...
76 views

### Floating Point Operations in Line Drawing Algorithms

When it comes to line drawing, DDA is the simplest and most intuitive algorithm, the core idea being: compute the slope of the line for every increment in x, increment y by the slope However, DDA is ...
82 views

### Unsolved Problems in CQ to this day?

What problems haven't been solved yet when it comes for instance in rendering,deferred rendering, Volumetric lighting, ambient occlusion or in any other interesting area. When i say unsolved problems, ...
48 views

### Why is cos(𝜃) in the denominator in the reflectance equation and in the numerator in the shading equation?

Background: I'm reading https://learnopengl.com/PBR to learn about PBR. In the theory slide (https://learnopengl.com/PBR/Theory), the author has the reflectant equation as The theta (the angle ...
29 views

### NURBS Weights De Boor's Algorithm

I am having trouble implementing an algorithm for 3rd degree NURBS. I have been able to program 2nd degree ones from the equations described here but I am not able to derive an equation for Rational B-...
108 views

### Do straight lines always remain straight when projected with a perspective camera?

If I have a straight line in 3D space and I use a camera matrix to do a perspective projection into a 2D plane/screen will the resulting line always be straight too? If I project the start point and ...
45 views

### Sphere Texture Mapping Algorithm

I am trying to generate UV coordinates automatically to map a texture on a sphere. The problem is with seams when going from 0.8 to 0.2 there is a discontinuity and interpolation in fragment shader ...
67 views

### Why is it easier to inverse transform every object in a scene than to transform a camera?

My lecturer for a computer graphics (raytracing) paper has stated that 'It is easier to apply the inverse transform to the world than it is to apply the transform to the camera.' The example given was ...
48 views

### How to implement physically based unit in pbr renderer

According to this note, Frostbite use photometry unit in their calculation. I am trying to mimic this feature, but I am not sure what transformation need to be done. I will try to explain what I have ...
32 views

### Difficulty including GLM into Visual Studio with OpenGL

I have been trying to implement GLM (math library) into Visual Studio with OpenGL. I have followed and watched many online resources that point me to include only the GLM folder inside the ...
46 views

### Very efficient/fast marching cube implementation

I was wondering if there's any known technique/algorithm that would compute a mesh generated by the marching cubes but hierarchically (like a divide and conquer strategy), in the implementation I know ...
23 views

### Identify plane of symmetry in 3D mesh

Is there an efficient way to identify the plane of symmetry in a 3D mesh? Preferably with existing code / software but if anyone knows how to implement it that would also be helpful. Example of the ...
16 views

### Open source tools for extracting hi-res images from video

I found recently an article in which they describe a technique to extract high resolution images from a standard quality videos. The technique exploits the fact that in a typical video the camera ...
60 views

### How to draw depth-based volume in real-time

Normally when we talk about realistic transparent volumes, we care about refraction (and total internal reflection), and we care about scattering. But there's a much simpler case of volume ...
51 views

### Organic 2d tree generation

I'm looking for a code to generate organic 2d trees like thiskind of shapes Gerard Ferrandez has an example to generate some tree but not organic like the picture shape https://codepen.io/ge1doot/pen/...
37 views

### How to translate the center of an equirectangular projection?

I'm trying to perfectly align two or more equirectangular photos of the same place taken from slightly different positions. Using an example provided by openMVG I managed to get the relative position ...
72 views

### smallpt: ray scattering and Importance Sampling

Introduction For those familiar with smallpt by Kevin Beason: In path tracing, when rays hit a surface, they are scattered and the theta angle (the angle between the normal to the surface and the ...
42 views

### What are the parameters measure the performance of a rendering? [closed]

Let's say I designed a housing model and rendered it using a rendering engine. how can I measure the performance of my rendering?
56 views

### Should I expect differences with explicit light sampling other that the noise?

I am trying to understand why my explicit light sampling implemetation does not produce the same results as my naive path tracer. Here are my results : Naive Version : Explicit light sampling ...
31 views

Hi I'm trying to get a better understanding of the BRDF modeling. I only implemented naive diffuse(lambert), specular and microfacet BRDF before, but I don't have much experience in mixed BRDFs and ...
81 views

### smallpt: when to stop diffuse ray scattering

For those familiar with smallpt, the ray tracer in 99 lines: I am checking the code, and there is something that is not clear to me in the DIFFUSE ray scattering. After the rays are shot, they keep ...
120 views

### Why does opengl use 4d matrices for everything?

What I managed to figure out is that the first 3*3 is used for rotation and scale and the 1*3 at the end is used for position, but what is the bottom row used for? is it only for clipping related ...
19 views

### Help with efficient quadtree vertices indexing to avoid redundancy

I am creating a quad tree from ground zero, because I am going to collapse it from bottom up I am refining it with a certain LoD level. I am using glm for mathematics and opengl for rendering. ...
93 views

### SSAO - artifacts appearing

I am trying to implement SSAO using DirectX11 but instead I got white screen with few black dots on model. My suspect is that kernel generation or usage might be wrong. I've tried changing order of ...
47 views

### Clarifying vulkan glsl std140

So I have a uniform block that looks something lile this { mat4; mat4[128]; uint[16] } The block should total up to 8320 bytes. After aligning by 256 bytes for nvidia, that brings the total ...
52 views

### 2D Line of Sight + Visibility Calculations

I am currently working on an algorithm to calculate visibility in a 2D top-down level. The level contains actors, with position and "sight" information walls, ...
44 views

### How to hide a part of a geometry dynamically using a shader in three.js

I have a very big geometry in three.js and I want to hide a section of that geometry along an axis (for example every vertex with a Z>N must be hidden). My idea is to create a custom shader in GLSL ...
111 views

### Where do “fireflies” come from?

I'm using a renderer developed by other people, and I found there are fireflies. It is strange that in a completely diffuse scene, there are still fireflies presented. To my understanding, I think it ...
101 views

### How to account for self intersection with large ray tracing scenes?

I'm working on a hybrid real time ray tracing project and trying to tackle the problem of self-intersection with larger scenes due to loss of float accuracy. The logic I'm trying to use is based on ...
38 views

### Compute shader textures compared 2D float4 arrays

I am wondering is there a difference in performance between using floating point textures as my 2D float4 array vs just passing in 2D float4 arrays? 2D float arrays eliminate the need to do texture ...
36 views

### Weight space in libigl

I'm trying to use the function of libigl uniformly_sample_two_manifold, but it does not work as described and there is no documentation whatsoever to help me understand why. I have a 3D mesh ...
38 views

### Anti aliasing thin features in textures

Assume I have a texture with a repeating line pattern. The lines are exactly 2 texels wide (really thin). Ans very spaced out (50 texels in between each line). I am now struggling with the ...