Computer Graphics CSCI 375

1. Computer GraphicsCSCI 375

2. What do I need to know? • Familiarity with • Trigonometry • Analytic geometry • Linear algebra • Data structures • OOP

3. Computer Graphics (& Related Areas) • Graphics • 3D model => 2D image • Image processing • Computer vision • 2D image => 3D model

4. Applications • Movies • Video games • Visualization • Simulation

5. Image Processing • Manipulate 2D bitmaps • Applies directly to pixel grid • Color correction • Scaling • Blurring • Sharpening

6. Image Synthesis • Graphics deals with image synthesis • Synthesis of 2D image from 3D scene description is called rendering

7. Photorealistic Rendering • Indistinguishable from reality • Ray tracing

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

10. Non-Photorealistic Rendering • Non-photoreal rendering • artificial water colors • pencil sketches • paint brushstrokes • Scientific and medical visualization

12. Computer Vision • 2D images => 3D model • Aspects of AI

13. Animation • Sequence of images • May be generated by physical simulation • Rigid bodies • Deformable objects • Gasses, liquids • Particle effects • Character animation

14. Modeling • Creating 3D geometric data • 3ds Max, Maya • Procedural modeling algorithms • Digitizers and computer vision • Mesh simplification

15. Raster Graphics • Modern displays are raster based • Pixels and subpixels • Old style vector displays

16. Framebuffer • Framebuffer • Space for final image • Grid of pixels • Colors are usu. 24 bits • Depth (z) • Usu. on GPU

17. Primitives • Complex scenes built from simpler objects • Objects built from primitives • Point • Line • Triangle

18. 3D Models • Collection of triangles • Each triangle stores 3 vertices • Vertex • position • color • normal

19. 3D Models • struct Vector3 { • float x, y, z; • }; • struct Vertex { • Vector3 position; • }; • struct Triangle { • Vertex vertices[3]; • }; • class Model { • std::vector<Triangle> triangles; • };

20. Traditional Graphics Pipeline • Primitives processed in stages • Transformation • Lighting • Clipping • Scan conversion • Fragment processing

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

22. The Graphics Pipeline Modeling Transformations • Primitives are processed in stages • Each stage forwards result to next stage Illumination (Lighting) Viewing Transformation (Perspective / Orthographic) Clipping Projection (to Screen Space) Scan Conversion(Rasterization) Visibility / Display

23. Transformation • Transformations • Rotation • Translation • Scales • Projection • Matrices

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

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

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

27. Lighting • Vertex or fragment color • Different light types • Shadows, reflections, and translucency

28. Lighting Modeling Transformations • Vertices lit according to material properties, surface properties (normal) and light sources • Local lighting model (diffuse, ambient, Phong, etc.) Illumination (Lighting) Viewing Transformation (Perspective / Orthographic) Clipping Projection (to Screen Space) Scan Conversion(Rasterization) Visibility / Display

29. Clipping • Camera and view volume • Culling • Clipping • Outputs visible primitives

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

31. Scan Conversion • Scan conversion or rasterization • 2D primitives => pixels • Per-vertex data is interpolated across the triangle

32. Scan Conversion (Rasterization) Modeling Transformations • Rasterizes primitives into pixels • Interpolate values as we go (color, depth, etc.) Illumination (Lighting) Viewing Transformation (Perspective / Orthographic) Clipping Projection (to Screen Space) Scan Conversion(Rasterization) Visibility / Display

33. Fragment Processing • Output of rasterization • Set of fragments • Z-values • … • Z-buffer algorithm • Texturing and transparency operations

34. 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)

35. Supporting Infrastructure OpenGL Application GLEW GLUT GL GLX, WGL Graphics Drivers Windowing System (X, Windows) GPU

36. 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

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

38. 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 • }