1 / 80

OpenGL and Parametric Curves

OpenGL and Parametric Curves. Advanced Multimedia Technology: Computer Graphics Yung-Yu Chuang 2005/12/21. with slides by Brian Curless, Zoran Popovic, Robin Chen and Doug James. Review of graphics pipeline. Transformation. Review of graphics pipeline. Projection & clipping.

jonathanray
Download Presentation

OpenGL and Parametric Curves

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. OpenGL and Parametric Curves Advanced Multimedia Technology: Computer Graphics Yung-Yu Chuang 2005/12/21 with slides by Brian Curless, Zoran Popovic, Robin Chen and Doug James

  2. Review of graphics pipeline Transformation

  3. Review of graphics pipeline Projection & clipping

  4. Review of graphics pipeline • Rasterization • Visibility

  5. Review of graphics pipeline • Shading

  6. Hierarchical modeling: a robot arm

  7. First implementation

  8. Better implementation

  9. OpenGL implementation

  10. Hierarchical modeling

  11. Implementation

  12. Human with hands

  13. Better implementation

  14. OpenGL implementation

  15. OpenGL • A low-level OS-independent graphics API for 2D and 3D interactive graphics. • Initiated by SGI (called GL at early time) • Implementation, for Windows, hardware vendors provide suitable drivers for their own products; for Linux, we have Mesa.

  16. Helper libraries • OpenGL does not provide OS-dependent functions such as windowing and input • GL: core graphics functions • GLU: graphics utilities in top of GL • GLUT: input and windowing functions

  17. How does it work? • From the programmer’s view • Specify geometric properties of the objects • Describe material properties • Define viewing • Define camera and object transformations • OpenGL is a state machine • States: color, material properties, line width, current viewing • States are applied to subsequent drawing commands • Input: description of geometric objects • Output: shaded pixels

  18. How does it work • From the implementer’s perspective • Graphics pipeline Primitives + material properties Is it Visible? 3D to 2D Scan conversion Visibility determination Display Rotate Translate Scale

  19. Primitives: drawing a polygon // put GL into polygon drawing mode glBegin(GL_POLYGON); // define vertices glVertex2f(x0, y0); glVertex2f(x1, y1); glVertex2f(x2, y2); glEnd(); Code available at http://www.xmission.com/~nate/tutors.html

  20. Primitives Hardware may be more efficient on triangles; stripes require less data

  21. Polygon restrictions • In OpenGL, polygons must be simple and convex not simple not convex

  22. Attributes • Part of the state of the graphics pipeline • Set before primitives are drawn. • Remain in effect! • Example: • Color, including transparency • Reflection properties • Shading properties

  23. Primitives: material properties • glColor3f(r,g,b); All subsequent primitives will use this color. Colors are not attached to objects. The above command only changes the system states. • OpenGL uses red, green and blue color model. Each components are ranged within 0 and 1.

  24. Primitives: material properties

  25. Simple transformations • Rotate by a given angle (in degrees) about ray from origin through (x,y,z) glRotate{fd}(angle, x, y, z); • Translate by a given x, y, z values glTranslate{fd}(x, y, z); • Scale with a factor in the x, y, and z directions glScale{fd}(x, y, z); • glPushMatrix(); glPopMatrix();

  26. Orthographic projection • glOrtho(left, right, bottom, top, near, far);

  27. Camera transformations • gluLookAt(eyex, eyey, eyez, cx, cy, cz, upx, upy, upz);

  28. Example: drawing a box

  29. Example: drawing a shaded polygon

  30. Initializing attributes

  31. Callback functions • Handle “events”, Idle, Keyboard, Mouse, Menu, Motion, Reshape • The display callback is installed by glutDisplayFunc()

  32. Actual drawing function

  33. Results glShadeModel(GL_FLAT) glShadeModel(GL_SMOOTH)

  34. Depth buffer in OpenGL • glutInitDisplayMode(GLUT_DEPTH); • glEnable(GL_DEPTH_TEST); • glClear(GL_DEPTH_BUFFER_BIT);

  35. Double buffering • Flicker if drawing overlaps screen refresh • Solution: use two frame buffers • Draw into one buffer • Swap and display, while drawing other buffer • glutInitDisplayMode(GLUT_SINGLE) • glutInitDisplayMode(GLUT_DOUBLE) • glutSwapBuffers()

  36. Example: rotate a color cube • Step 1: define the vertices

  37. Example: rotate a color cube • Step 2: enable depth testing and double buffering

  38. Example: rotate a color cube • Step 3: create window and set callbacks

  39. Example: rotate a color cube • Step 4: reshape callback, enclose cube, preserve aspect ratio

  40. Example: rotate a color cube • Step 5: display callback, clear, rotate, draw, flush, swap

  41. Example: rotate a color cube • Step 6: draw cube by drawing faces, orientation consistency

  42. Example: rotate a color cube • Step 7: drawing face

  43. Example: rotate a color cube • Step 8: animation, set idle callback spinCube()

  44. Example: rotate a color cube • Step 9: change axis of rotation using mouse callback

  45. Example: rotate a color cube • Step 10: toggle rotation or exit using keyboard callback

  46. Mathematical curve representation

  47. Parametric polynomial curves

  48. Cubic curves N too small → less flexibility in controlling the shape of the curve N too large → often introduce unwanted wiggles

  49. Compact representation

  50. Constrain the cubics Hermite: defined by two endpoints and two endpoint tangent vectors Bezier: defined by two endpoints and two other points that control the endpoint tangent vectors Spline: defined by four control points

More Related