# All Questions

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### 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 ...
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### 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 ...
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### 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 ...
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### 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. ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 : ...
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### How to match Blenders polynomial lens distortion model with GLSL?

I'm trying to re-implement Blenders (libmv) polynomial lens distortion model using shadertoy, in order to apply the lens distortion in another application ideally by generating a STMap for that. I ...
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### 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 ...
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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 $N = ... • 179 7 votes 0 answers 707 views ### Perspective-Correct Texture Mapping I am working on a small rendering engine for a personal project and I am having issues with the texture mapping part of it. It seems to work for some cases, but not for others. For example, when one ... • 71 7 votes 0 answers 279 views ### Cannot use more than a couple of MB in a shader storage buffer I am implementing a simple ray tracer with OpenGL. I have a shader storage buffer with all the triangles so I can test them for intersections in a compute shader. It works fine up to a certain buffer ... • 171 7 votes 0 answers 142 views ### Injecting Virtual point lights into 3D Grid I am currently trying to implement light propagation volumes in DirectX 11 and I have already done the RSM part which contains position, normal, depth and flux map generation. But for Injecting ... • 253 6 votes 0 answers 217 views ### Noise shaping for dithering with gamma? The context of this question is correct dithering of color with gamma correction. In dithering we add (shaped) noise$n$to a signal$s \in [0, 1]$based on a random variable$r \in [0, 1]$s' = s +... • 186 6 votes 0 answers 713 views ### How to account for self intersection with large ray tracing scenes? I'm working on a hybrid real time ray tracing project and trying to tackle the problem of self-intersection with larger scenes due to loss of float accuracy. The logic I'm trying to use is based on ... 6 votes 0 answers 589 views ### Avoiding Mach band effect when using multiple lights I wrote a simple Phong shader with two directional lights for a project, and noticed an unpleasant artifact in the lighting. Where both lights are illuminating the same region, dark bands appear at ... • 2,372 6 votes 0 answers 571 views ### How does path tracing handle specular surfaces(Dirac BSDFs) such as water? I'm trying to render water using path tracing. However, since in path tracing, the light sampling is skipped while the intersection point is perfect specular and thus no direct light would be taken ... • 293 6 votes 0 answers 236 views ### How is Ambient Occlusion calculated in "Deep Screen Space"? The paper (http://resources.mpi-inf.mpg.de/DeepScreenSpace/) just says that "The ambient occlusion contribution of a surfel to a pixel [..] as well as the influence radius [..] are computed ... • 143 6 votes 0 answers 458 views ### In Metal, what performance advantages are there, if any, to using vertex descriptors and the [[stage_in]] qualifier? Metal seems to provide two very different ways to access vertex data in your vertex shader. You can: Create an MTLVertexDescriptor object, which describes vertex ... • 413 6 votes 0 answers 1k views ### OpenGL texelFetch causes black stripes THE SHORT VERSION In my fragment shader I'm reading (using texelFetch) multiple times the same texel from a texture (created by another fragment shader) and write it to the output render buffer. ... • 313 6 votes 0 answers 124 views ### Form Factors confusion in Radiosity papers I feel a bit confused about the use of$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 ... • 161 6 votes 0 answers 912 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 ... • 231 6 votes 0 answers 342 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 ... • 1,229 6 votes 0 answers 128 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 ... • 901 5 votes 0 answers 57 views ### Facetted look when using SampleBias I am writing a simple material system for a game. Each material can have a specular value (phong) that is translated into "smoothness" via environment map. Similar to PBR, I compute a ... • 171 5 votes 0 answers 777 views ### How to implement PCSS correctly? I'm trying to implement PCSS in OpenGL/GLSL, but I have problems understanding the details especially the conversions between the coordinate spaces. The existing implementations are so different from ... • 151 5 votes 0 answers 502 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 ... • 61 5 votes 0 answers 286 views ### Why is Forward Rendering/Shading named this way? Forward rendering is the 'classic' approach to the rendering pipeline. Nowadays it is mostly replaced by a more flexible, deferred rendering approach. I did some research and had trouble finding ... • 151 5 votes 0 answers 213 views ### How to use Photometric Units with Rendering Equation? So I was just reading up on how to create more Physically Based Lights and wandered into the realm of photometry. I read the paper "Moving FrostBite to PBR" and in it the author claims he decided to ... • 2,393 5 votes 0 answers 381 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 0 answers 140 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(...
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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-...
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### 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 ...
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### 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 ...
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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......
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### 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 ...
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### How to draw an orthogonal graph from its edges and vertices data?

I am writing a software and I need to represent an graph in a orthogonal manner from topological data (vector of edges,vertices and their connectivity data) Graphs consist of a set of vertices and a ...
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### Polygon Filling rule - even odd OR orientation of the normal

I am going through some ideas that slice a 3D model and fill the area of the resulting polygon contour . Currently they are using the following concepts as follows: Every resulting line of the ...
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### Which interpolation algorithm does MS Paint on Windows 7 use for image rescaling?

I was about to scale this image down to 64x64 pixels: The result I got on MS Paint on Windows 7 was surprisingly good (i.e. crisp edges): , whereas scaling it with GIMP resulted in for cubic and ...
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### OpenSCAD Hull/Minkowski function by hand?

I am trying to model an organic object using OpenSCAD. However this will need to be ported over to older software. This restricts the primitives I can use (only cone, cylinder, torus, sphere and cubes)...
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### 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 ...
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### 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 ...
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### Indexing gl_TessLevelOuter[] with gl_InvocationID on a tessellation control shader

I'm using hardware tessellation to render a terrain mesh with variable LOD. I have this snippet on my tessellation control shader: ...
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### Incorrect instanced rendering

Previously, to render a bunch of quads, I was simply using a few uniforms (one for a model matrix and another for the texture layer ID). However, I'd rather not have to loop through each quad and set ...
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### CUDA cuMemcpuHtoD vs cuMemcpy2D

Asking it here and not on SO as it seems to be appropriate question for CG. I am learning NVIDIA NVENC API.The SDK supplies a sampled called "NvEncoderCudaInterop" .There is a chunk of code which ...
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### Manually fetching 8 neighboring texels from 3D texture greatly decreases performance

I'm implementing manual interpolation between texels in a 3D texture to be able to discard some of them when needed. Compared to hardware interpolation, this process takes a lot of time. If I simply ...
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### Watertight Mesh Representation

A watertight mesh is one which does not have holes, and for which each face has a designated inside and outside. Such a mesh can be "tetrahedralized", has a defined volume, and can be an ...
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