I’ve noticed the term ‘physically-based shading’, or variants thereof, used with increasing frequency these days. I’m happy about this, since it represents a movement away from hacking around with magic numbers and formulae in shaders, towards focusing on the underlying material and lighting models. It offers consistency, predictability and constraints where previously these had been somewhat lacking. There was a great course at Siggraph this year purely about physically based shading. The trouble is, I’m still not really sure exactly what it means… Energy Conservation When looking at material response,…

# Category: Graphics

## Derivative Maps

I recently came across an interesting paper, Bump Mapping Unparametrized Surfaces on the GPU by Morten Mikkelsen of Naughty Dog. This paper describes an alternative method to normal mapping, closely related to bump mapping. The alluring prospect of this technique is that it doesn’t require that a tangent space be defined. Mikkelsen is apparently well-versed in academic obfuscation (tsk!), so the paper itself can be a little hard to read. If you’re interested in reading it, then I would recommend first reading Jim Blinn’s original bump mapping paper to understand…

## UI Anti-Aliasing

I’ve been working on making a really simple IMGUI implementation for my engine at home. I like to do a little bit of research when I’m approaching something new to me like this, so I went hunting around for publicly available implementations. While doing this, I came across Mikko Mononen’s implementation in Recast. I was impressed when I ran the demo with how smooth his UI looked. It turns out that he’s using a little trick (which I’d never seen before, but I’m sure is old to many) to smooth…

## What’s wrong with this picture?

Well, you could point out a number of things to answer that question. There’s some pretty obvious aliasing, a random pixel on the ground which should be in shadow but isn’t, it’s noisy, boring etc. But that’s not my point. The point is: It’s too dark! I know it’s too dark because I know how I rendered it, and I rendered it wrong. It still kind of looks acceptable (well to me at least) though. I’m not sure that I would say that it’s implausibly dark if I didn’t know…

## Direct3D 11 Multithreading

I’ve been putting it off for a while, but with my recent trip to GDC and the arrival of the Direct3D 11 beta, I thought it was about time I switched my renderer to be multithreaded. One of the things I learned at a Direct3D 11 talk at GDC is that it works on ‘down-level hardware’, which means DirectX 9 & 10 cards. Of course, you don’t get the snazzy new hardware features, but you do get some of the benefits of the new API, like multithreading and limited compute…

## Energy Conservation In Games

Recently at work I was chatting with a colleague, and the topic of energy conservation for specular reflections came up. This reminded me that I’ve been sitting on a blog post for a while about just this subject, so I thought it was time to finish it. First of all, I’d like to start by looking at the standard diffuse reflection model. In games, the typical formula for calculating diffuse reflection from a particular light is: Where Cd is the diffuse material color, Li is the light color, N is…

## Irradiance Caching: Part 2

In my previous post, I wrote very briefly about an important improvement to the irradiance caching algorithm – irradiance gradients – and I’m going to expand on rotational gradients this time. Gradients The gradient of a function represents both the direction and rate of change of that function as the inputs vary. For a one dimensional function this is simply the derivative of the function. As you move into higher dimensions, you need to consider which coordinate system the inputs for the function are specified in, as this will change…

## Irradiance Caching: Part 1

Solving the rendering equation with even just one bounce of indirect lighting can take a long time. The majority of time spent rendering a frame is in estimating the lighting integral. For example, rendering a single bounce of indirect lighting at 720p resolution with 256 sample rays for a Monte Carlo estimator requires about 237 million rays to be cast. This doesn’t even include the rays needed for sampling the lights for direct lighting, so in practice, the total will be even higher. One interesting observation made by Greg Ward…

## Better Sampling

A couple of days ago, I compared the images my ambient occlusion integrator produced with those of Modo using similar settings. I noticed immediately how much ‘cleaner’ the render from Modo was. Clearly there was an issue with the way I was picking my samples, so I set about improving things. My approach for generating the ambient occlusion rays was to generate uniform random samples over the hemisphere about the normal. Based on two random numbers in the range [0,1), I calculate the normalized sample direction using the following function:…

## The Holidays: Time for fun work!

For the first time in about three years, I’ve had two weeks off work. I’ve spent a lot of time just relaxing and taking a break from things, but I’ve also been able to get back to doing some graphics work. Ever since Vivendi bought Activision, the project that I was leading has been “put on hold”, so I’ve been back on the game team. It’s not as fun for me, that’s for sure, but luckily, I have my code at home to play with, so all is not lost!…