Stylized Environmental Rendering Michael Lester

Background Rendering of natural environments is very difficult for photorealistic real-time graphics It is very expensive and the results are often unsatisfactory. Apply Non-photorealistic rendering (NPR) techniques to render a natural environment. This is traditionally a very difficult area of real-time graphics. That's where Non-photorealistic rendering comes in Or stylized rendering, I'll use the two interchangeably

Stylized Rendering Generate images that appear don't adhere to real-world rules Convey information without being precise and complete Stylized Rendering solves this problem in two ways The generated images (can) take less time to compute because they are not as complex, yet they still convey the same information And they can often look ''better” The human brain can easily pick out errors in a photorealistic image (since we see them every day) But stylized images don't have this problem For example, in the screenshot on the left, you can clearly recognize an ocean, even though most of the water is a simple, flat blue On the right, you can tell that the torches are burning, but the flames are much more simple than realistic fire

The Goal Apply artistic techniques to interactive graphics Traditionally animated film NPR research papers Solve rendering problems by using an NPR style Use the GPU as much as possible Applicable to Games The goal of my research is (very broadly) to study the techniques that artists use in illustrating outdoor environments, and apply them to real-time computer graphics More specifically I'm interested in grass or fields and how characters interact with them This leads to two paths of research: I'll need to study traditionally animated film to pick out their techniques And then apply them by building on Research in the area of Non- Photorealistic Rendering Another of my goals for this project is to use the GPU as much as possible Much of the research that is applicable to this project does not take full advantage of modern hardware. The NPR field blossomed before programmable shaders became available, So many techniques are CPU heavy or rely on the fixed-function pipeline, which means they are quite slow I'd like my system to take full advantage of the GPU This means using the programmable shaders to do most of the work And behind it all is the idea that I'd like my work to be applicable to games Fast, easy to implement, and inexpensive

How do artists solve the problem? They have it easy Fixed viewpoint allows for image- based effects Use several “tricks” that can be adapted to interactive graphics So how do Artists handle grassy environments? Well, they've got it easy Film and images have a single, fixed viewpoint. This means that they can get away with a lot, Such as using a single static texture for grass. Games, however, have arbitrary viewpoints. This is the main challenge in adapting animation techniques to games. For example, When games use a single, static texture for grass, it is very obvious because of the lack of parallax when the viewpoint changes. However, many of their tricks are applicable to interactive graphics It just might take some work

“Deep” Grass Grass is simply a plane Artists create the illusion of depth Only the silhouette is significant One technique that I think is quite applicable to games, and that I am focusing on, is deep grass In this image, the artist creates the illusion of depth by using the silhouette only The grass is just a simple plane, but the jagged overlapping of the grass on the character's edges make him appear to be sinking into the field This is very applicable to games because characters often interact with grass by walking through it. Many stylized games simply use a static grass texture But this technique could be implemented very efficiently and would be a significant improvement

Applying to Graphics Graftals Based on a paper by Markosian and Kowalski A small texture element attached to an object Represented with by a small geometric “fin” Affected by viewing angle, distance, geometric collision, etc. Abstracts the scene complexity away from the geometry So how do we implement this for Real-Time Graphics? We can use a concept known as Graftals Originally proposed in two papers by Kowalski and Markosian They are basically small, specifically textured geometric fins that are placed all around an object They differ from normal geometry because they are decoupled from the modeled scene geometry They are not always drawn And they're not always drawn the same way For example, graftals are commonly drawn only near the edges of objects Or where to objects intersect, such as a character moving through a field This has the affect that the Rendering engine now controls scene complexity, instead of the geometric models. This gives the engine a lot of power It can keep the level of detail consistant across the scene Procedural animation is much easier Which is great for wind effects Control the rendering cost easily It can be reduced if the system is heavily taxed

The System Preprocessing – calculating intial graftal positions Level of Detail (LOD) – Scaling, Styling, Abstracting based on viewing distance Rendering – Drawing the graftals and silhouette edges The system that I intend to develop can be split in to 3 basic stages Preprocessing Graftals need a place to live! The original Graftal papers used manually placed graftals I'd like to extend that by generating the initial positions using surface- constrained particle systems Level of Detail, also known as LOD When the viewer gets farther away, the object should become more abstract, else we risk having an extremely noisy image There are many ways to handle this The straightforward approach is to reduce the number of graftals on the object, but other effects are possible LOD can also be affected by variables like viewing angle or Time of Day Rendering Drawing the actual graftals and their silhouette edges Previous systems haven't taken advantage of new hardware advancements such as programmable Geometry Shaders Their is much room for improvement here

Progress Pure research for now Code framework running Development begins next week Eurographics 2011 Intend to submit a Short Paper Follow progress at realtimemike.wordpress.com Currently in the research stage I have a rendering framework (basically a graphics only game engine) up I'm beginning coding the system next week The Eurographics conference has put out a call for Short Papers Due in December I'll be submitting a short paper on this work (and praying it gets in!) If you're interested at all you can follow my work at this website. Thanks!

Thank You!