All Questions

14
votes
0answers
472 views

What exact algorithm and parameters reproduce L-system plant growth figure in Algorithmic Beauty of Plants

I am interested in duplicating a figure (shown below, ch 1 fig 1.21) in the book Algorithmic Beauty of Plants. The book is available here http://algorithmicbotany.org/papers/#abop This image appears ...
11
votes
0answers
237 views

Why does increasing simplex noise dimension wash it out?

I just tried using this approach to create a tiling 2d simplex noise function with Gustavson's java implementation. The result tiled, but the texture seemed muddy / washed out. I decided to compare ...
10
votes
0answers
193 views

Choosing width of data for signed distance field texture

A signed distance field texture is a technique where you store the distance from a pixel to the surface of a shape within the color information for that pixel, allowing almost vector graphics quality ...
10
votes
0answers
373 views

Problem with definition of BSDF and radiance

When I was reading theory behind physical based rendering I noticed that definition of BSDF and radiance has some problems. For example BSDF of purely specular surfaces is zero almost everywhere and ...
9
votes
0answers
295 views

Using Monte carlo on Rayleigh scattering

Update I am editing and posting this question in a different way; this time from the point of view of Nishita paper. Sunlight gets scattered at P and attenuated before reaching Pv. Therefore ...
9
votes
0answers
121 views

Help with start up bias in Metropolis Light Transport

I'm trying to implement metropolis light transport based on this paper, and I have the basic thing working. I run the algorithm multiple times with different starting points, add the results for each ...
9
votes
0answers
253 views

WebGL packing/unpacking functions that can roundtrip all typical 32-bit floats

I have a WebGL circuit simulator. One of the problems it has is that, due to using quite a lot of intermediate float textures as it simulates, it doesn't work on various mobile devices. They only ...
9
votes
0answers
401 views

How correct is rendering in XYZ / linear RGB space?

I have a spectral power distribution (SPD, 5 nm steps) for all light sources in the scene and SPDs for the reflectance of all surfaces under any light / viewer angle in question. I'm going to ...
9
votes
0answers
120 views

How to describe the bi-directional links for the Weiler-Atherton algorithm?

My postscript interpreter currently implements the Hodgeman-Sutherland clipping algorithm but this is limited to simpler shapes and doesn't have a provision for utilizing various winding-number rules. ...
8
votes
0answers
590 views

More accurate Fresnel approximation for a RGB-based Path Tracer

I'm writing a path tracer and, for the moment, spectra related data (spectral power distributions and spectral reflectance curves) are stored as RGB tuples. In the Cook-Torrance specular BRDF I am ...
8
votes
0answers
346 views

3D mesh segmentation simple algorithm

I am developing the algorithm reported in this article: Least square conformal mapping. Here is presented an algorithm to flat a 3d mesh on the parametric space, but i don't understand the ...
7
votes
0answers
169 views

Supersampling HDR

I'm encountering some issues supersampling in HDR for an SDR result and was curious what the usual method for doing this is. Notice how pixelated the edge of the white sphere is. Here's how I render ...
7
votes
0answers
924 views

Diffuse BRDF component of the Disney BRDF

In the SIGGRAPH course: BURLEY B.: Physically Based Shading at Disney, SIGGRAPH 2012 Course: Practical Physically Based Shading in Film and Game Production, 2012. it is mentioned that some BRDF ...
7
votes
0answers
876 views

Bump mapping a ray-traced sphere

I'm attempting to apply a height map to a ray-traced sphere. The height map is stored as a texture. I have the intersection point on the sphere $p$, and I compute the normal vector at that point $N = ...
7
votes
0answers
506 views

OpenGL texelFetch causes black stripes

THE SHORT VERSION In my fragment shader I'm reading (using texelFetch) multiple times the same texel from a texture (created by another fragment shader) and write it to the output render buffer. ...
7
votes
0answers
71 views

Form Factors confusion in Radiosity papers

I feel a bit confused about the use of $F_{ij}$ and $F_{ji}$ in Radiosity papers. $F_{ij}$ should be the fraction of energy leaving patch $i$ that arrives at patch $j$. If you take the original ...
7
votes
0answers
153 views

Cannot use more than a couple of MB in a shader storage buffer

I am implementing a simple ray tracer with OpenGL. I have a shader storage buffer with all the triangles so I can test them for intersections in a compute shader. It works fine up to a certain buffer ...
7
votes
0answers
123 views

Injecting Virtual point lights into 3D Grid

I am currently trying to implement light propagation volumes in DirectX 11 and I have already done the RSM part which contains position, normal, depth and flux map generation. But for Injecting ...
7
votes
0answers
282 views

Code runs differently on different hardware

I wrote a 2D fluid-solver in OpenGL (code here) some time back. While it runs flawlessly on my onboard Intel GPU, the simulation very quickly "blows-up" when same code is run using nvidia card : ...
6
votes
0answers
62 views

Drawing “after” Present to achieve better performance

I had an application that was originally single threaded and worked as follows: gather the items to be drawn (occlusion / frustrum culling / sorting into batches) draw items using an immediate ...
6
votes
0answers
153 views

Avoiding Mach band effect when using multiple lights

I wrote a simple Phong shader with two directional lights for a project, and noticed an unpleasant artifact in the lighting. Where both lights are illuminating the same region, dark bands appear at ...
6
votes
0answers
211 views

How is Ambient Occlusion calculated in “Deep Screen Space”?

The paper (http://resources.mpi-inf.mpg.de/DeepScreenSpace/) just says that "The ambient occlusion contribution of a surfel to a pixel [..] as well as the influence radius [..] are computed ...
6
votes
0answers
315 views

Cascaded shadow maps. Seams between cascades

I implemented cascaded shadow maps, where shadow maps for each cascade is rendered to one canvas: The light projections for each cascade are calculated from the bounding spheres of camera sub-...
6
votes
0answers
152 views

Dual paraboloid shadow texture edge seams

I implemented dual paraboloid shadows for point lights. The goal was to reduce the number of shadow passes. Also the target is GLES3.0 so no layered rendering is available. The shadows work, and ...
6
votes
0answers
106 views

Is there any open-source implementation of n*log(n) visibility graph construction algorithm?

Is there any open-source implementation of n*log(n) visibility graph construction algorithm? I'm trying to understand S. K. GHOSH and D. M. MOUNT sweep line algorithm, but it's known for having very ...
6
votes
0answers
756 views

What prevents older GPUs from supporting Vulkan?

More out of curiosity than for any practical purpose, I'm wondering what is lacking from older GPUs that causes them to be unable to support Vulkan. I know that some argue that some hardware, such as ...
6
votes
0answers
437 views

Percentage-closer Soft Shadows implementation

I am trying to implement the Percentage-closer Soft Shadows (PCSS) from NVidia inside Unity but I am facing some issue and I don't know where they come from and then, I do not know how to solve them......
6
votes
0answers
57 views

Early exit strategy for SSAO

I'm working on an SSAO implementation. I've had an idea to speed it up by having AO fragment shader finish faster for fragments that are not occluded (depending on the scene, this can be a significant ...
6
votes
0answers
276 views

Perspective-Correct Texture Mapping

I am working on a small rendering engine for a personal project and I am having issues with the texture mapping part of it. It seems to work for some cases, but not for others. For example, when one ...
6
votes
0answers
552 views

Drawing to framebuffer texture - texture then split in half

I am doing exercises from the OpenGL SuperBible 6th Ed. I have managed to set up rendering into a framebuffer texture and then rendering from that texture to a cube. But for some reason, when the ...
6
votes
0answers
170 views

scan line conversion

I am going throug the topic scan line conversion where the scan line parallel to the x-axis is put through the intersection test with all the edges of the polygon. Would there be any large ...
5
votes
0answers
40 views

Ask for help on understanding a formula related to change of variable

Although I have tried for a long time, I cannot understand Eq.(11) of paper "Microfacet Models for Refraction through Rough Surfaces" written by Bruce Walter, Stephen Marschner, Hongsong Li and ...
5
votes
0answers
144 views

Ray tracing implicit surfaces using Sturm's theorem

I am trying to render implicit surfaces given by a polynomial equation $F(x,y,z) = 0$ using Sturm's theorem. Plugging the parametric ray equation $r(t) = o + td$, where $o\in\mathbb{R}^3$ is the ray ...
5
votes
0answers
196 views

How does path tracing handle specular surfaces(Dirac BSDFs) such as water?

I'm trying to render water using path tracing. However, since in path tracing, the light sampling is skipped while the intersection point is perfect specular and thus no direct light would be taken ...
5
votes
0answers
81 views

How to properly color particles in N body sim?

In my n-body simulation I would like to color the particles in way which corresponds to the magnitude of the net force acting on them. This is so that I can confirm visually that the particles ...
5
votes
0answers
203 views

In Metal, what performance advantages are there, if any, to using vertex descriptors and the [[stage_in]] qualifier?

Metal seems to provide two very different ways to access vertex data in your vertex shader. You can: Create an MTLVertexDescriptor object, which describes vertex ...
5
votes
0answers
108 views

Computation of conservative AABB for clipped triangle

I'm currently trying to implement a fast algorithm for KD-Tree construction using SAH, as described in this paper: On building fast KD-trees for ray tracing, and on doing that in O(N log N) I found ...
5
votes
0answers
127 views

CrazyBump Shape Recognition

I've recently been using CrazyBump, and I think I'm starting to understand how it works. But I'm confused about what it calls Shape Recognition. According to this website, that feature attempts to add ...
5
votes
0answers
120 views

What is the potential equation in PBR?

I'am studying PBR and the book introduce the potential equation. They said the potential equation can describe shooting algorithms better, and $W(x, \theta)$ describes the fraction of the radiance $L(...
5
votes
0answers
112 views

How is glint rendering done in Ray Tracing?

How is glint rendering done with ray tracing in the photo below? Is it just a simple normal map? I found a paper online that describes the exact same method used in the photo above but I have no ...
5
votes
0answers
52 views

Is it possible to create a forced focus with a dual layer of images in order to Avoid eye strain with Virtual and Augmented Reality?

Would eye tracking allow for the alignment of a dual layered image (a google glass like device and a screen or projection) to provide a way to force the focus of the eyes into to a real life ...
5
votes
0answers
95 views

Should I use nonsymmetric BSDF for refraction in BPT?

I'm implementing bidirectional path tracing. I want to simulate perfect refraction. I read in the Veach thesis that a perfect refraction BSDF is non-symmetric. Does it mean that I need to use ...
5
votes
0answers
361 views

OpenGL ES vertex/fragment shaders - Blinn phong

I'm developing a simple educational project to study OpenGL ES. I'm try to render some simple OBJ models using Blinn-Phong. The first version of the of my implementation calculate all the lighting ...
5
votes
0answers
517 views

How to disable Perspective Correction in Texture Coordinates Interpolation in OpenGL(without using shaders)?

I need to do planar reflection mapping in OpenGL. By using a virtual camera (with a reversed camera ray) at the back of reflective plane (a mirror), I rendered the scene to texture, which is then ...
5
votes
0answers
257 views

How to make double working in OpenGL 4.1 on OS X ( Intel HD Graphics 5000 )?

I've recently rebuild shaders for my program and it stopped "working" ( black screen ) on OS X ( El Capitan ), but it's ok on Linux on GTX 660. I've tested it on another Apple hardware and it worked ...
5
votes
0answers
118 views

How much processing power does stenciling actually save?

For example, let's assume I'm rendering cascaded shadow mapping, but for whatever reason, instead of one of the typical approach, I do the following: Render the lowest resolution shadowmap Copy part ...
4
votes
0answers
65 views

Anisotropic GGX BRDF implementation. How is it related to isotropic GGX BRDF?

Introduction I am implementing anisotropic GGX BRDF and have encountered strange behaviour of my implementation. I thought that if I compare the microfacet distribution function I have with the one ...
4
votes
0answers
36 views

Does MRG32k3a compare well with PCG and Xorshift256*?

I've been using standard 32-bit Xorshift in my GPU path-tracer for a while, following Nathan Reed's approach with hashed seeds and decorrelated state. I (finally) discovered today that Xorshift is ...
4
votes
0answers
100 views

Direct3D Global Atomic Issue

Recently I ran into an odd issue with some of my DirectX11 DirectCompute code when trying it on an AMD GPU for the first time where as on a NVIDIA one it had worked fine all through development. The ...
4
votes
0answers
74 views

Predicting reflectance functions from complex surfaces

There are three principal ways to obtain a BRDF. We can Derive an analytic formula using physical principles Use simulation given an assumed or measured model of the surface microgeometry Measure ...

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