Computer Graphics CSCI 375

COMPUTER GRAPHICSCSCI 375

What do I need to know?

Familiarity with Trigonometry

Analytic geometry

Linear algebra

Data structures

OOP

Computer Graphics (& Related Areas) Graphics

3D model => 2D image

Image processing

Computer vision 2D image => 3D model

Applications

Movies

Video games

Visualization

Simulation

Image Processing

Manipulate 2D bitmaps

Applies directly to pixel grid Color correction Scaling Blurring Sharpening

Image Synthesis

Graphics deals with image synthesis

Synthesis of 2D image from 3D scene description is called rendering

Photorealistic Rendering

Indistinguishable from reality

Ray tracing

PhotorealRendering

CG Choice Award Gallery:http://forums.cgsociety.org/forumdisplay.php?f=121

Non-Photorealistic Rendering Non-photoreal rendering

artificial water colors

pencil sketches

paint brushstrokes

Scientific and medical visualization

Computer Vision

2D images => 3D model

Aspects of AI

Animation

Sequence of images

May be generated by physical simulation Rigid bodies Deformable objects Gasses, liquids Particle effects

Character animation

Modeling

Creating 3D geometric data

3ds Max, Maya

Procedural modeling algorithms

Digitizers and computer vision

Mesh simplification

Raster Graphics

Modern displays are raster based

Pixels and subpixels

Old style vector displays

Framebuffer

Framebuffer Space for final image

Grid of pixels

Colors are usu. 24 bits

Depth (z)

Usu. on GPU

Primitives

Complex scenes built from simpler objects

Objects built from primitives Point Line Triangle

3D Models

Collection of triangles

Each triangle stores 3 vertices

Vertex position color normal

3D Models

struct Vector3 {float x, y, z;

};

struct Vertex {Vector3 position;

};

struct Triangle {Vertex vertices[3];

};

class Model {std::vector<Triangle> triangles;

};

Traditional Graphics Pipeline Primitives processed in stages

Transformation

Lighting

Clipping

Scan conversion

Fragment processing

The Graphics PipelineModeling Transformations

Illumination(Lighting)

Viewing Transformation(Perspective / Orthographic)

Clipping

Projection (to Screen Space)

Scan Conversion(Rasterization)

Visibility / Display

The Graphics Pipeline

Primitives are processed in stages

Each stage forwards result to next stage

Modeling Transformations



Clipping




Transformation

Transformations Rotation Translation Scales Projection

Matrices


3D models defined in own coordinate system (object/local space)

Modeling transforms orient models within a common coordinate frame (world space)




Clipping




Object space World space

Viewing Transformation Maps world space to eye

space Viewing position is

transformed to origin & direction is oriented along some axis (usually z)




Clipping




Eye space

World space

Projection Objects are projected to 2D

image place (screen space)




Clipping




NDC Screen Space

Lighting

Vertex or fragment color

Different light types

Shadows, reflections, and translucency

Lighting

Vertices lit according to material properties, surface properties (normal) and light sources

Local lighting model (diffuse, ambient, Phong, etc.)




Clipping




Clipping

Camera and view volume

Culling

Clipping

Outputs visible primitives

Clipping Transform to Normalized

Device Coordinates (NDC)

Remove portions of object outside view volume




Clipping




Eye space NDC

Scan Conversion

Scan conversion or rasterization 2D primitives => pixels

Per-vertex data is interpolated across the triangle

Scan Conversion (Rasterization)

Rasterizes primitives into pixels

Interpolate values as we go (color, depth, etc.)




Clipping




Fragment Processing

Output of rasterization Set of fragments Z-values …

Z-buffer algorithm

Texturing and transparency operations

OpenGL

Open Graphics Library (OpenGL) Standard specification defining a cross-

platform API for writing 2D and 3D graphics apps

Cell phones to supercomputers Developed by SGI in 1992 Current version 4.4 Managed by non-profit Khronos Group

Consortium focused on open, royalty-free standards for authoring and acceleration of parallel computing, graphics, and dynamic media (OpenCL, OpenGL, OpenGL ES, WebGL, COLLADA)

Supporting Infrastructure

OpenGL Application

GLEW GLUT

GLX, WGL

Windowing System (X, Windows)

GPU

Graphics Drivers

GL

OpenGL Example

Drawing a colored triangle glBegin (GL_TRIANGLES); glColor3f (1.0f, 0.0f, 0.0f); glVertex3f (-1.0f, -1.0f, 0.0f); glColor3f (0.0f, 1.0f, 0.0f); glVertex3f (+1.0f, -1.0f, 0.0f); glColor3f (0.0f, 0.0f, 1.0f); glVertex3f (0.0f, +1.0f, 0.0f); glEnd ();

Inefficient; we’ll improve upon this

OpenGL Program Organization main () { // Initialize and create window // Set up key and mouse event handlers // Initialize OpenGL // Set up lighting // Load assets

OpenGL Program Organization (Cont’d) // Update and render loop while (userWantsToContinue) { // Clear screen // Specify camera position & orientation

(pose) for (Model model : scene) { // Specify object pose // Draw model // Frame completion code (buffer swap) } // Cleanup code }

Documents

Computer Graphics CSCI 375