1. Game Programming 06 The Rendering Engine
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 Video Games
Purpose of the rendering:
Photorealism
Stylized look (cartoon, sketch, watercolor and so on)

4. Describing a Scene Scene is composed of objects: Opaque (solid) object
Surfaces (triangles) define its shape
Don’t care about inside
Transparent object

5. Representing object (surface)
Surface: a two-dimensional sheet composed of an infinite number of points in 3D
Representation
Analytical form (parametric surface equation)
Collection of Patches
Triangle mesh

6. Representing object (surface)
Analytical form (parametric surface equation)
Ex.) Sphere equation

7. Representing object (surface)
Collection of Patches
Patch: a simple rectangular surfaces
Similar to a quilting
Ex.) NURBS, Bezier Surfaces, Subdivision Surface
Quilt
NURBS surface
NURBS modeling

8. Representing object (surface)
Triangle mesh
A piece-wise linear approximation to the surface
Piece-wise linear approximation to a function
Piece-wise linear approximation to a surface

9. Representing object (surface)
Triangle mesh
Using a triangle because:
It is the simplest type of polygon
It is always planar
It still remains a triangle after transformations such as affine (projective) transformation
All graphics card support a hardware acceleration to draw it

10. Triangle Mesh Tessellation LOD (Level-of-detail)
A process of dividing a surface up into a collection of triangles
LOD (Level-of-detail)

11. Triangle Mesh Winding Order
How to define the front/back face direction
Counterclockwise (CCW) / Clockwise(CW)
Counterclockwise winding order
Computing normal direction

12. Triangle Mesh
Representation of mesh
Triangle list
: 점의 좌표

13. Triangle Mesh Representation of mesh Indexed Triangle List : 점의 좌표 1 21 2 3 4 5 6 7
Vertex list:
Indexed triangle list:

14. Triangle Mesh Other representation of mesh Triangle strip Triangle fan
Vertex list:
Triangle strip
Triangle fan

15. Model space
Positions of a triangle mesh’s vertices are usually specified relative to a local coordinate system. (front/left/up)
left up
front

16. World space and mesh instance
Individual meshes are located in a scene (world)
Mesh instance:
Any one mesh might appear many times in a scene
Representation:
Reference mesh, and its transformation matrix
red: model coord.
black: world coord.

17. Visual properties of a surface
Information needed to define a final color in the rendered image:
Direction of surface normal
Diffuse color
Shininess/reflectivity
Roughness
Texture
Opacity or transparency
Other optical properties
: How light should interact with the surface

18. Introduction to Light
What we see is a result of complex interactions of light with matter.
Four main interactions of light
Absorption
Reflection
Transmission / refraction (bent)
Diffraction

19. Introduction to Light
Absorbed by a surface
Why does red look red?

20. Introduction to Light
Reflected by a surface

21. Introduction to Light Transmitted through a media
Partially absorbed or refracted

22. Color model Color model: how to represent a color
RGB (Red-Green-Blue):
RGB888 (8 bit for each channel: 0~255 integer) – 24 bit
RGB565 (5 bit for red, and blue, 6 bit for green) – 16 bit
HSV (Hue-Saturation-Value)
LDR (Low Dynamic Range) vs. HDR (High Dynamic Range)
HDR: RGB in a higher precision (float value)

23. Color model
LDR with various exposes and tone mapping

24. Alpha channel Representing opacity
A fourth channel to RGB  RGBA or ARGB
RGBA8888 – 32 bit per pixel
RGBA5551 – 16 bit per pixel

25. Vertex Attributes Position vector (x, y, z) Vertex normal (nx, ny, nz)
Diffuse color (dr, dg, db)
Specular color (sr, sg, sb)
Texture coordinates (u, v)
Skinning weights (w1, w2, …)

26. Attribute interpolation
Flat shading and Gouraud shading
Gouraud Shading:
Inside color is interpolated from the vertex colors

27. Texture maps
To overcome the per-vertex attribute, using image to fill-in the polygons

28. Texture maps
To overcome the per-vertex attribute, using image to fill-in the polygons + =

29. Texture maps Texture coordinates:
2D coordinate system defined on an image
Denoted as (u,v): uv-coordinate u u v v

30. Types of textures Types of textures Diffuse map Bump map Normal map
Gloss map
Environment map

31. Types of textures
Diffuse map
describing diffuse surface color

32. Types of textures Bump map (similarly displacement map)
Describes small perturbations in height
A sphere without bump mapping (left). A bump map to be applied to the sphere (middle). The sphere with the bump map applied (right)

33. Types of textures Normal map: encodes normal vectors Low vs. high res.
Low res. + diffuse map
Low res. + diffuse + normal

34. Types of textures Gloss map (similarly specular map)
encoding how shiny a surface should be

35. Types of textures Environment map
containing a picture of surrounding environment for reflection

36. Mipmapping
Different resolution of the texture with respect to the distance between an object and a camera

37. OGRE::Mesh in action Get the sample file at our home page
Create your own cylinder mesh from scratch.