1. Shadowing SET09115 Intro Graphics Programming

2. Breakdown • Basics • Occluders and receivers • Types of shadows • General Techniques • Blob shadows • Multiple point lights • Other Techniques • Using textures • Volumetric shadowing

3. Recommended Reading • Real-Time Rendering • Chapter 9 is about global illumination • Section 9.1 about shadowing • Section 9.2 about ambient occlusion • Not covering in lecture

4. Basics

5. Why do we mean by Shadowing? • Shadowing is when we add to a rendered scene darkened areas to imply the occlusion of light • Something in the scene is blocking the current lighting model from fully illuminating a particular area • Shadowing is essentially the removal of light from a scene • Actually, shadowing in rendering is the adding of dark area to a normally rendered lit scene

6. Example

7. Why do we want Shadowing? • Shadowing adds realism to a rendered scene • Up until now, we have used lighting and texturing to add realism • Any 3D scene without shadowing looks wrong, artificial • Goal of any 3D rendering is to look correct, real even if cheating • Shadowing can also be a gameplay feature

8. Example • Splinter Cell • http://www.youtube.com/watch?v=gaRN5Dr_jBI • Thief • http://www.youtube.com/watch?v=AP8EyFmWg44

9. Occluders and Receivers • A shadow is created when a light source is occluded on a surface • There are three parts to consider • The light source • The occluder • The receiver

10. Types of Shadows • There are two types of shadows that can form part of a scene • Hard Shadows • Soft Shadows • Our task is to add the correct type of shadowing, and in a realistic manner • This can be complicated

11. Hard Shadows • Hard shadows are those caused by point lights • Have definite outlines • Have a single uniform colour • Quite easy to work out in relation to soft shadows

12. Soft Shadows • Soft shadows are caused by other lighting mechanisms • Area lights • Light volumes • Soft shadows have a blurring effect at the edges • Difficult to get right • And expensive

13. Umbra and Penumbra • A soft shadow is made of two parts • Umbra • Penumbra • The hard shadow is not the umbra • Light changes based on size of light

14. Questions?

15. General Techniques

16. Shadow Blobs • The simplest technique for shadowing is to project a blob onto the ground plane • Size of blob changes based on distance • Eye is quite forgiving, and will accept this as a reasonable shadow

17. Example • Super Mario 64 • http://www.youtube.com/watch?v=DTzs9bcNgMQ

18. Planar Shadows • A better technique is to do a two stage render • Shadow pass renders a projection onto a plane • Shadow is rendered onto the ground plane

19. Example • Oblivion • http://www.youtube.com/watch?v=OBbW86Hl7wI

20. Light Viewer • Another technique is to perform a render pass using the light’s position as the render position • Generate the depth map from this render pass • Use this depth map to determine what parts of the scene are to be shadowed • This provides a similar approach to standard projection lighting

21. Multiple Point Lights • Another common technique • Soft shadows can be created by using multiple point lights in a scene • Each point light creates a shadow • Shadows are accumulated and then used in the final render

22. Questions?

23. Other Techniques

24. Using Textures • We can do some pre-processing and work out light maps for a scene • Pre-process as in before running the application • Much faster than using real-time, dynamic shadows

25. Using Textures • When performing a render, we can generate the shadow map during the shadowing stage • For fixed scenes, these shadow maps can be reused • Pre-process

26. Stencil Buffer • Buffer commonly used for shadowing techniques • Stencil buffer is another per-pixel buffer, similar to the depth buffer • The information contained in the stencil buffer can be set for various uses • Number of failed pixel writes due to occlusion • Simplest use of the stencil buffer is to determine which areas cannot be rendered to during a render pass • For example shadowed regions

27. Volumetric Shadows • Volumetric shadows are one of the techniques used by the stencil buffer • The stencil buffer can be incremented based on depth information when renders are performed

28. Example

29. Good Shadowing • http://www.youtube.com/watch?v=PjqsYzBrP-M

30. Questions?

31. To do this week… • I’m not going to produce a practical for this week or next • Concentrate on the coursework • I will put the practicals together and post on WebCT over the next few weeks • So you can see what to do • I’ve added some new geometry code to WebCT • Drawing spheres and torus’ for lighting and texturing

32. Summary • Shadowing is another technique for adding realism • And another technique where we cheat to gain realism • We have only really scratched the surface with techniques here • Read Real-Time Rendering if you are interested • Maths is in there as well • We aren’t looking at shadowing as part of the assessment • We will be impressed if you add it though