COMPUTER GRAPHICS CSCI 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

Photoreal Rendering CG Choice Award Gallery: splay.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 triangles; };

Traditional Graphics Pipeline  Primitives processed in stages  Transformation  Lighting  Clipping  Scan conversion  Fragment processing

The Graphics Pipeline Modeling 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 Illumination (Lighting) Viewing Transformation (Perspective / Orthographic) Clipping Projection (to Screen Space) Scan Conversion (Rasterization) Visibility / Display

Transformation  Transformations  Rotation  Translation  Scales  Projection  Matrices

Modeling Transformations  3D models defined in own coordinate system (object/local space)  Modeling transforms orient models within a common coordinate frame (world space) Modeling Transformations Illumination (Lighting) Viewing Transformation (Perspective / Orthographic) Clipping Projection (to Screen Space) Scan Conversion (Rasterization) Visibility / Display Object spaceWorld space

Viewing Transformation  Maps world space to eye space  Viewing position is transformed to origin & direction is oriented along some axis (usually z) Modeling Transformations Illumination (Lighting) Viewing Transformation (Perspective / Orthographic) Clipping Projection (to Screen Space) Scan Conversion (Rasterization) Visibility / Display Eye space World space

Projection  Objects are projected to 2D image place (screen space) Modeling Transformations Illumination (Lighting) Viewing Transformation (Perspective / Orthographic) Clipping Projection (to Screen Space) Scan Conversion (Rasterization) Visibility / Display 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.) Modeling Transformations Illumination (Lighting) Viewing Transformation (Perspective / Orthographic) Clipping Projection (to Screen Space) Scan Conversion (Rasterization) Visibility / Display

Clipping  Camera and view volume  Culling  Clipping  Outputs visible primitives

Clipping  Transform to Normalized Device Coordinates (NDC)  Remove portions of object outside view volume Modeling Transformations Illumination (Lighting) Viewing Transformation (Perspective / Orthographic) Clipping Projection (to Screen Space) Scan Conversion (Rasterization) Visibility / Display Eye spaceNDC

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.) Modeling Transformations Illumination (Lighting) Viewing Transformation (Perspective / Orthographic) Clipping Projection (to Screen Space) Scan Conversion (Rasterization) Visibility / Display

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 GLUTGLX, WGL Windowing System (X, Windows) GPUGraphics 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  }