Game Programming 06 The Rendering Engine

Game Programming 06The Rendering Engine 2010년 2학기 디지털콘텐츠전공

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

Rendering in Video Games • Purpose of the rendering: • Photorealism • Stylized look (cartoon, sketch, watercolor and so on)

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

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

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

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

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

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

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

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

Triangle Mesh • Representation of mesh • Triangle list : 점의 좌표

Triangle Mesh • Representation of mesh • Indexed Triangle List : 점의 좌표 0 1 2 3 4 5 6 7 Vertex list: Indexed triangle list:

Triangle Mesh • Other representation of mesh • Triangle strip • Triangle fan Vertex list: Triangle strip Triangle fan

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

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.

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

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

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

Introduction to Light • Reflected by a surface

Introduction to Light • Transmitted through a media • Partially absorbed or refracted

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)

Color model • LDR with various exposes and tone mapping

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

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, …)

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

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

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

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

Types of textures • Types of textures • Diffuse map • Bump map • Normal map • Gloss map • Environment map

Types of textures • Diffuse map • describing diffuse surface color

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)

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

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

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

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

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

Game Programming 06 The Rendering Engine