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CMT2300 ----Fundamentals of Computer Graphics

CMT2300 ----Fundamentals of Computer Graphics. Revision. Week 11. Dr. Xiaohong Gao BG---Room 2C23 www.cs.mdx.ac.uk/staffpages/xiaohong/cmt2300. Course work --- Project : Animation. Between 1 to 4 minutes To be submitted by May 2, week12 .

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CMT2300 ----Fundamentals of Computer Graphics

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  1. CMT2300 ----Fundamentals of Computer Graphics Revision Week 11 Dr. Xiaohong Gao BG---Room 2C23 www.cs.mdx.ac.uk/staffpages/xiaohong/cmt2300

  2. Course work --- Project : Animation • Between 1 to 4 minutes • To be submitted by May 2, week12. • Please include a self-addressed-envelope to get feed back. • To achieve distinction • some extra features apart from lectures should be included, such as • Visual C++ features: buttons, menus, etc.. • Animation techniques: 3D, Double Buffering, etc..

  3. Exam • 3 questions chosen from 5 questions. • Each question carries 25 marks. • Total marks are 75. • Review lecture notes. • Review Seminar exercises. • www.cs.mdx.ac.uk/staffpages/xiaohong/cmt2300.html

  4. 1. Review of Previous lectures (1/3) - points - lines - curves • Output primitives - translation - scaling - rotation • Geometric Transformations

  5. 1. Review of Previous lectures (2/3) - translation - scaling - rotation - reflection • Matrix representation of transformations - Timer - Event - Tweening - Morphing - Double buffering • Animation Techniques

  6. 1. Review of Previous lectures (3/3) - 2D view pipeline - 3D viewing pipeline • Viewing Pipeline - OnDraw - MoveTo - LineTo - SetTimer - pDC->Ellipse(*) - pDC->Rectangle(*) • Useful Visual C++ Methods and Functions

  7. 2. Output primitives • the basic building blocks for pictures are referred as output primitives. • Routines for generating output primitives provide the basic tools for constructing pictures. • E.g., character strings, “a”, “Welcome to CMT2300”. • Geometric entities --- points, straight lines, curved lines, filled areas (polygons, circles, etc.).

  8. Example 1: Mathematical representation of lines and circles Lines: y = a x + b Cicles: x2 + y2 = r2//r is the radius

  9. 3. Geometric Transformation (0) • Geometric Transformation refers to changes of objects in orientation, size, and shape. • These changes alter the co-ordinate description of objects. • It is very useful in computer animation in altering or manipulating displays.

  10. 3. Transformation ---- Scaling • scaling: • alter the size of an object • objects are scaled according to scaling factors sx, sy Change of sx Change of sy original

  11. 3. Transformation --- translation (2) • A translation is applied to an object by re-positioning it along a straight-line path from one co-ordinate to another. • To translate a two-dimensional point by addingtranslation distances, tx, ty, to the original co-ordinate. • Translation is a rigid-body transformation that moves objects without deformation. (0,0) (0,0)

  12. 3. Transformation --- Rotation (3) • Rotation is a 2D transformation. • Rotation is to reposition an object along a circular path in the a xy plane. • Objects rotated according to angle of rotation theta (). • Rotation is by a given angle () • - if  >0, rotation is anticlockwise • - if  <0, rotation is clockwise

  13. 3. Transformation ---- Reflection (4) • A reflection is a transformation that produces a mirror image of an object with reference to a specific line. • This line can be thought as a mirror. • The points are transformed by being moved to their corresponding positions on the other side of the mirror. • This line can be a standard line, such as x-axis, or y-axis. • This line can also be an arbitrarily defined line.

  14. 4. Matrix Representation of Transformations (1) T(tx, ty) = S(sx, sy) = R() =

  15. 4. Matrix Representation of Transformations (2) • Reflection about the line y = 0, the x axis, the matrix is • Reflection about, the y axis, flips x coordinate, the matrix is

  16. 4. Matrix Representation of Transformations (3) • Reflection about, the origin and passes origin, the matrix is

  17. Example 2: For each of the following transformations, sketch the final position of the house after 2 transformations: 1). Translate (50, 0) then rotate (0,0, 90) 2). Rotate(0, 0, 90) then translate(50, 0)

  18. 1). Translate (50, 0) then rotate (0,0, 90) 50 1 25 2 -50 -25 25 50 75 -25 -50

  19. 1). Rotate(0, 0, 90) then translate(50, 0) 50 25 -50 -25 25 50 75 -25 1 2 -50

  20. 5. Animation techniques (1) ---- Timer Example 3: Explain the usage of CTimer object in Visual C++ using the following line. SetTimer(1, 10, NULL); • CTimer object is used to control events • It is very useful for computer animation. • SetTimer(1,10,NULL) means timer fires every 10 milliseconds. • The above line should be created on OnCreate() method or others. • Also, a windows message handler has to be added to CxxView class. • Invalidate(TRUE) is to be added to CxxView “OnTimer()” method. • Or Invalidate( TRUE) has to be added to “OnDraw()” method.

  21. 5. Animation techniques (2) ---- Storyboard Example 4: Explanation of animation “storyboard” in terms of key frames and the usefulness of the key frames in designing sequences. • Storyboard in computer animation is an outline of the action. • It defines motion sequence as a set of events that are to take place. • Depending on the type of animation to be produced, the storyboard could consist of a set of rough sketches or key frames. • A key frame is a detailed drawing of the scene at a certain time in the animation sequence.

  22. 5. Animation techniques (3) ---- Morphing • Transformation of objects shapes from one form to another. • Morphing method can be applied to any motion or transition involving a change to shape.

  23. 5. Animation techniques (4) ---- Double buffering Example 5: Explain how double buffering can overcome some of the problems of the draw-clear-redraw methods of animation. • Viewer never sees blank screen (unless desired as part of the animation) • Viewer does not see construction of scene regardless of complexity of scene. • Most graphics systems provide fast methods to swap buffers, so better animation achieved without having to reduce number of frames (i.e. avoids problems of introduction of pause). • The technique can be scaled up with multiple buffers for pre-construction of scenes when complex scenes would slow down animation if attempted in real time.

  24. 6. The 2D & 3D viewing-transformation pipeline Construct World-Coordinate Scene Using Modeling-Coordinate Transformations Convert World-Coordinates to Viewing Coordinates WC MC VC MapViewing Coordinates to Normalized Viewing Coordinates using Window-Viewport Specifications Map Normalized Viewport to Device Coordinates NVC DC

  25. 7. Visual C++ Methods (1) Example 6: draw a line y = x pDC->MoveTo (10,10); pDC->LineTo(50,50);

  26. 8. Visual C++ Methods (2) • Example 6: Briefly describe each of the following Visual C++ graphics functions from device contents, including the parameters they accept and sketching an example for the application of each function in a program: • MoveTo • Rectangle • Ellipse

  27. MoveTo is to move device context to the point, • such as pDC->MoveTo (0,0) • Rectangle is to draw a rectangle: • e.g., pDC->Rectangle(0,0,100,100) • Ellipse is to draw a ellipse confined by a rectangle, e.g. • CRect tt(0,0,100,100); • pDC->Ellipse(tt);

  28. Good Luck !

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