1. Game Programming 09 OGRE3D Lighting/shadow in Action
2010년 2학기
디지털콘텐츠전공

2. Rendering in Video Games
Depth-Buffered Triangle Rasterization
Virtual Scene
Virtual Camera
Various Light Sources
Visual Properties
Solving the Rendering Equation (Shading Equation)

3. Rendering in OGRE3D Depth-Buffered Triangle Rasterization
Virtual Scene  createScene()
Virtual Camera  createCamera()/ createViewport()
Various Light Sources  createScene()
Visual Properties  material
Solving the Rendering Equation (OGRE3D engine)

4. What does make a scene look real?
Material
Lighting (shade + shadow)

5. OGRE3D Lighting Three types of lighting in OGRE3D
Point (Ogre::Light::LT_POINT)
Point light sources emit light from them in every direction.
Spotlight (Ogre::Light::LT_SPOTLIGHT)
A spotlight works exactly like a flashlight does.
Directional (Ogre::Light::LT_DIRECTIONAL)
Directional light simulates far-away light that hits everything in the scene from a direction.

6. Creating a Light Creating a Light Setting a type Setting a position
SceneManager::createLight(“name”)
Setting a type
Ogre::Light::setType( … )
LT_POINT, LT_DIRECTIONAL, LT_SPOTLIGHT
Setting a position
Ogre::Light::setPosition( Ogre::Vector3(x,y,z) )
Ogre::Light* pointLight = mSceneMgr->createLight("pointLight");
pointLight->setType(Ogre::Light::LT_POINT);
pointLight->setPosition(Ogre::Vector3(0, 150, 250));

7. Setting a Light Setting the color Setting the direction
Ogre::Light::setDiffuseColour (Ogre::ColourValue(r,g,b))
Ogre::Light::setSpecularColour (Ogre::ColourValue(r,g,b))
Setting the direction
Ogre::Light::setDirection( Ogre::Vector3(x,y,z))
Setting the spot light property
Ogre::Light::setSpotlightRange (inner_angle, outer_angle)
angle: Ogre::Degree(angle)
Ogre::Light* directionalLight = mSceneMgr->createLight("directionalLight");
directionalLight->setType(Ogre::Light::LT_DIRECTIONAL);
directionalLight->setDiffuseColour(Ogre::ColourValue(.25, .25, 0));
directionalLight->setSpecularColour(Ogre::ColourValue(.25, .25, 0));
directionalLight->setDirection(Ogre::Vector3( 0, -1, 1 ));

8. Shadow Shadows are: There are many techniques to render shadows.
one of the most challenging aspects of 3D rendering
still very much an active area of research.
There are many techniques to render shadows.
None is perfect and they all come with advantages and disadvantages

9. How to draw a shadow? Off-line algorithm Real-time algorithm
Ray tracing shadow
Real-time algorithm
Projected planar shadows
Shadow mapping (texture-based shadow)
Stencil Shadow Volume

10. Ray Tracing Shadow

11. Projected Planar Shadows
The simplest technique to create shadows from an object.
Two-pass algorithm
Draw the object
Draw the shadow
Problem:
Only on a planar surface

12. Shadow Mapping
Testing whether a pixel is visible from the light source by comparing it to a depth image of the light source's view
Depth image is stored as a texture  Texture-based shadow
Visualization of the
depth map projected
onto the scene
Scene rendered from the light view
Scene from the light
view, depth map.
Depth map test failures
Scene with shadow mapping

13. Shadow Mapping A problem of the shadow mapping:
Aliasing
How to solve the problem:
Increasing the resolution of the texture
Projective shadow map
single shadow map pixel

14. Stencil Shadow Volume
Stencil + Shadow Volume

15. Stencil buffer
Stencil buffer is like a mask.

16. Typical use of a stencil buffer
Drawing a reflection effect
Drawing a planar shadow
참고자료:

17. Shadow volume concept Shadow volume is constructed from occluders
Although we can create volumes for every triangle in the occluders, we only need the silhouette.
Different types of volume for different types of lights

18. Shadow Volume concept
All the objects positioned within a shadow volume are hidden from the light source and are thus in either full or partial shadow.
A silhouette edge can more generally be considered as an outline or edge separating a front- and back-facing surface.

19. Shadow Volume concept
A point light source and the shadow Volume

20. Stencil Shadow Volume
Render the Scene without lights and keep the z-buffer.
Fragments with non-zero stencil values are considered to be in shadow. The generation of the values in the stencil buffer :
Render front face of shadow volume. If depth test passes, increment stencil value
Render back face of shadow volume. If depth test passes, decrement stencil value
Render the lit area where the stencil buffer value is 0

21. Stencil Shadow Volume Stencil Shadow Volume in Action Shadow volume
in wireframe
Rendered with the shadow
Shadow volume

22. Stencil Shadow Pros Very accurate and robust Nearly artifact-free
Faceting near the silhouette edges is the only problem
Work for point lights and directional lights equally well
Low memory usage

23. Stencil Shadow Cons Too accurate — hard edges Very fill-intensive
Need a way to soften
Very fill-intensive
Scissor and depth bounds test help
Significant CPU work required
Silhouette determination
Building shadow volumes
Hard shadow
Soft shadow

24. Shadow in OGRE3D Multiple implementations about shadow
How to know where shadows are:
Stencil Shadow
Texture-based shadow
How to draw the shadows
Modulative shadows : darkening
Additive Light Masking : brightening

25. Enabling shadows Disabled by default Enabling a shadow technique
This should be the first thing of the scene setup.
Type can be stencil shadow or texture-based shadow
Create Lights. By default, they will cast shadows
To turn off the shadow:
Create Objects. By default, they will cast shadows
mSceneMgr->setShadowTechnique(ShadowType)
Calling Light::setCastsShadows(false)
Calling Entity::setCastsShadows(false)

26. Stencil Shadow Shadow Type either: Good thing: Bad thing:
Modulative Shadow SHADOWTYPE_STENCIL_MODULATIVE
Additive Light Masking SHADOWTYPE_STENCIL_ADDITIVE
Good thing:
Self-Shadow on low-end hardware
Bad thing:
Hard-shadow only
Slow because of a higher polygon count
mSceneMgr->setShadowTechnique(SHADOWTYPE_STENCIL_MODULATIVE)

27. Stencil Shadow Issues CPU overhead for shadow volume computation
Avoid any long shadows (e.g. a very low sun position)
Culling distant objects beforehand
Shadow volume accuracy
Don’t put any object too close to a light source
Mesh edge list
Edge list is necessary for constructing the shadow volume
Official exporter and tools will generate it automatically
If you use your own mesh, you can generate it by calling Mesh::buildEdgeList
Visible silhouette edge
Silhouette edge can be very marked.
Especially, the mudulative method is more vulnerable with 2 or more light sources
Additive lights do not suffer from this as badly because each light is masked individually

28. Texture-based shadow
Rendering shadow casters for the point of view of the light into a texture. Then, projected onto shadow receiver.
Type Name: SHADOWTYPE_TEXTURE_MODULATIVE SHADOWTYPE_TEXTURE_ADDITIVE
Good things:
Lower overhead
Hardware acceleration
Customisable (e.g. easy to make soft shadows)
Bad things:
Aliasing effect depending on the resolution
Only supports direction lights and spotlights

29. Texture-based shadow Configurations Maximum number of shadow textures
Shadow texture size
Shadow far distance
Shadow texture offset (Directional Lights)
Shadow fade settings

30. Modulative Shadow Drawing a scene without shadows
Darkening(modulating) the shadow area

31. Additive Shadow Drawing a scene with ambient light
Adding each light one by one
For this reason, rendering should be divided into several passes:
Ambient pass
Diffuse/specular pass
Decal pass

32. Additive shadow Pass spliting example material TestIllumination {
technique
pass
ambient
diffuse 1 0 0
specular
texture_unit
texture grass.png }

33. Additive shadow Pass dividing example // Ambient pass pass {
diffuse 0 0 0
specular 0 0 0 }
// Diffuse / specular pass
pass {
scene_blend add
iteration once_per_light
diffuse 1 0 0
specular }
// Decal pass
pass {
scene_blend modulate
lighting off
texture_unit
texture grass.png }