More Bi-Directional Path Tracing

It’s still not perfect, far from it in fact, but it’s progress none the less. I’ve been reading a lot lately about Metropolis Light Transport, Manifold Exploration, Multiple Importance Sampling (they do love their M names) and it’s high time I started implementing some of them myself.

So it’s with great sadness that I am retiring my PRT project which began over a year ago, all the way back at the start of my dissertation. PRT is written in Java, for simplicity, and was designed in such a way that as I read new papers about more and more complex rendering techniques I could easily drop in a new class, add a call to the render loop, or even replace the main renderer all together with an alternative algorithm which still called upon the original framework.

I added many features over time from Ray Tracing, Photon Mapping, Phong and Blinn-Phong shading, DOF, Refraction, Glossy Surfaces, Texture Mapping, Spacial Trees, Meshes, Ambient-Occlusion, Area Lighting, Anti-Aliasing, Jitter Sampling, Adaptive Super-Sampling, Parallelization via both multi-threading and using the gpu with OpenCL, Path Tracing, all the way up top Bi-Directional Path Tracing.

But the time has taken it’s toll and too much has been added on top of what began as a very simple ray tracer. It’s time to start anew.

My plans for the new renderer is to build it entirely in C++ with the ability to easily add plugins over time like the original. Working in C++ gives a nice benefit that as time goes by I can choose to dedicate some parts of the code to the GPU via CUDA or OpenCL without too much overhead or hassle. For now though the plan is to rebuild the optimized maths library and get a generic framework for a render in place. Functioning renderers will then be built on top of the framework each implementing different feature sets and algorithms.

Tags Bi-Directional Path Tracing, Concurrency, CUDA, Depth of Field, Global Illumination, GPGPU, Monte Carlo Integration, OpenCL, Path Tracing, Photon Mapping, Ray Tracing

A better Bi-Directional Path Tracer

So I’m back to working on this again.. It’s a lot better than before but it’s not perfect. I’m still using unweighted samples during path generation and I am still generating a fresh path (highly randomized in path traced -> light traced construction) for every sample. Because of this the noise that still persists in the image above will never feasibly go away. Today I plan to look at “Multiple Importance Sampling” a lot more in depth.

Tags Bi-Directional Path Tracing, Path Tracing

Bi-Directional Path Tracing

After a minor crisis that I am horribly unprepared to start my PhD in October I thought I’d try to delve back into the world of graphics with something simple (ha). I decided to try and extend my Java Path Tracer to support a rendering mode for Bi-Directional Path Tracing. Something which I now realize is easier said than done. Ideally if I had had the time I would have introduced Bi-Directional Path Tracing (BDPT) to my dissertation project last year; however, I simply never had the time to wrap my head around all the mathematics so I left it out.

The image above was rendered at 640 x 480 but I have downsampled the image here to 320 x 240 to make up for the fact I was only able to render 100 samples before my computer BSOD’d. That’s right, because if you can make a Java program cause a BSOD then you know something is terribly amiss. My theory is that it’s simply too much recursion for the JVM. Even though I am running the 64bit version with an increased memory quota the stack for function calls is still (annoyingly) a memory limited 32bit stack. And seeing as this is just a toy project I am working on whenever I start to panic about next year it doesn’t seem worth spending the time to convert the whole thing to an iterative renderer from a recursive one.

Tags Bi-Directional Path Tracing, Path Tracing

Dissertation is done!

Rejoice! For after one hell of a long year finally the dissertation is done dusted and thankfully handed in!

This was the final result, a real-time path tracer written in C using OpenCL to compute frames and OpenGl to render them. Here is a simple cornell box style scene that was left to converge for a couple of minutes.

My project fair demo. My graders seemed to like it (I bagged 92% for the Viva!) and so did the PhD students and my coursemates… Not so much praise from the school kids, the phrase “Realistic? Looks nothing like Call of Duty” was used…. First time I’ve ever wanted to smack a child jokes but what can you do. The tech industry people didn’t seem to care for it either which was rather miserable because I had to stand there for 5 hours in a boiling hot room while no one wanted to know about my work.

But I can’t really complain about not getting any job offers because… I got offered a summer research position unconditional fully funded PhD Studentship at the uni! So this summer I’ll be staying in Swansea to effectively continue this project with the goal of getting Path Tracing working much much faster and on mobile devices (tablets most likely).

Here’s an album showing the progress from start to finish throughout the year.

Tags Global Illumination, OpenCL, OpenGL, Path Tracing, Ray Tracing

Dissertation Update: Path Tracing in action

Thought I’d post an update of my dissertation project seeing as I haven’t posted anything in a while and my interim document is now submitted. As part of my progress towards GPU Accelerated Path Tracing I’ve modified the Java Ray Tracer shown previously to render using the Path Tracing algorithm. It’s a bit slow and clunky but for the most part it gets the job done.

The only problem has been that Java just isn’t cut out for this type of work. I don’t want to flare up the whole “Java is not week, it’s not 1995 any more…” debate but path tracing is just too much work for Java to handle. Even when running with additional memory and with the work split across an 8 core i7 processor StackOverflow’s are all to common a sight, and when they occur they ruin the image being rendered.

Below are some comparison images showing Ray Tracing (left), Photon Mapped Ray Tracing (middle), and Path Tracing (right).

And finally, here are some images showing the results of an experiment I ran looking into the possibility of performing constant time filtering techniques to under-sampled images in order to make them an acceptable quality for moving scenes. With a lot of trial and error I found that a good technique was perform a relatively cheap 3×3 Box Blur filter to smooth out any of the large dark noise areas and then to apply a 3×3 or 5×5 Median Filter to help retain edge definition while still smoothing the remaining noise.

Tags Global Illumination, Path Tracing, Ray Tracing