smallpt | smallpt Monte Carlo Path Tracer

by wedusk101 C++ Version: Current License: Non-SPDX

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kandi X-RAY | smallpt Summary

smallpt is a C++ library. smallpt has no bugs, it has no vulnerabilities and it has low support. However smallpt has a Non-SPDX License. You can download it from GitHub.

smallpt: global illumination in 99 lines of c++. author: kevin beason (kevin.beason [at] gmail.com) date: 10/11/2008. smallpt is a small monte carlo path tracer, and generates a single image of a modified cornell box rendered with full global illumination (gi). it does this by solving the rendering equation, including ideal lambertian, specular, and dielectric reflection, area lights, anti-aliasing, importance sampling, and multi-threading. it is only 99 lines of c++, but illustrates photo realistic rendering in a correct, and concise manner. the source code for a small program that path traces a simple cornell box and produces accurate results in a terse implementation is given, which provides an educational example to new graphics students (and seasoned alike), and yields a ground truth image, all in an easy to read package. never before has a correct, complete, and

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smallpt has a low active ecosystem.

It has 1 star(s) with 0 fork(s). There are 1 watchers for this library.

It had no major release in the last 6 months.

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smallpt has a Non-SPDX License.

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Community Discussions

Trending Discussions on smallpt

OpenCL ray tracer works fine on CPU but not (always) on GPU

Raytracer light reflection bug

QUESTION

OpenCL ray tracer works fine on CPU but not (always) on GPU

Asked 2020-Oct-15 at 15:29

[Please look at the edit below, the solution to the question could simply be there]

I'm trying to learn OpenCL through the study of a small ray tracer (see the code below, from this link).

I don't have a "real" GPU, I'm currently on a macosx laptop with Intel(R) Iris(TM) Graphics 6100 graphic cards.

The code works well on the CPU but its behavior is strange on the GPU. It works (or not) depending on the number of samples per pixel (the number of rays that are shot through the pixel to get its color after propagating the rays in the scene). If I take a small number of sample (64) I can have a 1280x720 picture but if I take 128 samples I'm only able to get a smaller picture. As I understand things, the number of samples should not change anything (except for the quality of the picture of course). Is there something purely related to OpenCL/GPU that I miss ?

Moreover, it seems to be the extraction of the results from the memory of the GPU that crashes :

...

ANSWER

Answered 2020-Oct-15 at 15:29

Since your program is working correctly on CPU but not on the GPU it could mean that you are exceeding the GPU TDR (Timeout Detection and Recovery) timer.

A cause for the Abort trap:6 error when doing computations on the GPU is locking the GPU into computation mode for too much time (a common value seems to be 5 seconds but I found contradicting resources on this number). When this occurs the watchdog will forcefully stop and restart the graphic driver to prevent the screen being stuck.

There are a couple possible solutions to this problem:

Work on a headless machine

Most (if not all) OS won't enforce the TDR if no screen is attached to them

Switch GPU mode

If you are working on an Nvidia Tesla GPU you can check if it's possible to switch it to Tesla Compute Cluster mode. In this mode the TDR limit is not enforced. There may be a similar mode for AMD GPUs but I'm not sure.

Change the TDR value

This can be done under Windows by editing the TdrDelay and TdrDdiDelay registry keys under HKEY_LOCAL_MACHINE -> SYSTEM -> CurrentControlSet -> Control -> GraphicsDrivers with a higher value. Beware to not put a number too high or you won't be able to know if the driver has really crashed.

Also take note that graphic drivers or Windows updates may reset these values to default.

Under Linux the TDR should already be disable by default (I know it is under Ubuntu 18 and Centos 8 but I haven't tested on other versions/distros), if you have problems anyway you can add Option Interactive "0" in your Xorg config like stated in this SO question

Unfortunately I don't know (and couldn't find) a way to do this on MacOS, however I do know that this limit is not enforced on a secondary GPU if you have it installed in your MacOS system.

Split your work in smaller chunks

If you can manage to split your computation into smaller chunks you may be able to not surpass the TDR timer (E.G. 2 computations that take 4s each instead of a single 8s one), the feasibility of this depends on what your problem is and may or may not be an easy task though.

Source https://stackoverflow.com/questions/64258611

QUESTION

Raytracer light reflection bug

Asked 2020-Feb-24 at 13:08

I'm trying to port the smallpt: Global Illumination in 99 lines of C++ to C# and I'm getting this weird bug when the light reflects of a diffuse surface. Does anyone have an idea where the problem might be coming from?

This what I'm getting with 40 samples

This is what it's supposed to look like

This my code for diffuse surfaces:

...

ANSWER

Answered 2020-Feb-23 at 16:41

The effect you are getting reminds me a bit of shadow acne. Usually this is a more circular pattern, which is why I'm not sure. Shadow acne happens due to float inaccuracies. When you scatter or reflect, you make a new ray from a certain origin on a surface in a direction. The origin will sometimes shift under/above the surface depending on the float inaccuracy. That's why you often offset the ray with a small number EPSILON in the direction of the normal. So your new origin becomes: intersection + intersection.normal * EPSILON. You should test different values for epsilon, but usually it's around 0.01 to 0.02 or something around that. In your code you are still using intersectionpoint, which I assume does not have the offset. I'm not sure if that will work, since your result looks a bit different from the shadow acne I'm used to, but it's worth a try right?

Source https://stackoverflow.com/questions/60363199

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