Input of graphical data
- 1. S.RAJAPRIYA Assistant Professor of IT rajapriya@vvvcollege.org
- 2. Graphics programs use several kinds of input data. Picture specification need values for Coordinate positions Character string parameters Scalar values for transformation Menu options Identification of picture parts
- 3. There are six logical device classification used by PHIGS and GKS. LOCATOR devices STROKE devices STRING devices VALUATOR devices CHOICE devices PICK devices
- 4. A device for specifying a coordinate position(x,y) Positioning the screen cursor at some location in a displayed scene Example of physical device: mouse, trackball, space-ball, thumbwheels,dials etc., Keyboards can be used for locator input in several device. Light pens have also been used.
- 5. To input a sequence of coordinate positions Physical device for generating locator input Translate continuous movement of cursor positioning device, such as mouse, into a series of input coordinate values The graphics tablet is one of the more common stroke device. Button activation can be used to place the tablet in continuous mode
- 6. Primary physical device used for string input – keyboard. Used for picture or graph labelling in computer-graphics applications
- 7. To set the scalar value for geometric transformations, viewing parameters and illumination parameters Also used for setting physical parameter such as temperature, voltage levels, stress factors,etc., Example of physical device: a panel of control dials, joystick, tablet Other technique for providing valuator input: Display the graphical representation of sliders, buttons, rotating scales and menu on the video monitor
- 8. Menus, typically used in graphics programs to select processing options, parameterValues and object shape Cursor positioning device are commonly choice device for a selecting menu Determine a menu item is selected by the cursor position (x,y) : •For a menu item with vertical and horizontal boundaries (xmin,xmax,ymin,ymax) •If the cursor position satisfy the condition xmin<=x<=xmax ymin<=y<=ymax •The menu is selected with the cursor position • The other choice devices are keyboard an voice entry.
- 9. To select a part of a scene that is to be transformed or edited in some way Picking can be performed by positioning the screen cursor and pressing a button or key to record the pixel coordinates Example of physical device: mouse, joystick, keyboard Other pick methods include highlighting schemes, selecting object by name or a combination of methods
- 10. Coordinate-extent tests do not uniquely identify a pick object Approach 1:Compute the distances from the pick position to individual line segments Calculate the perpendicular distance squared from a pick position to the line position to the line For a line segment with endpoints (x1, y1) , (x2, y2),the perpendicular distance squared from a pick position (x, y) is
- 11. Approach 2: Associate a pick window with a selected cursor position–the pick window is centered on the cursor position Example: A pick window with center (x,y), width w and height h Highlighting other method used to facilitate picking other method used to facilitate picking successively highlight those objects whose coordinate extent overlap a pick position (or pick window) user could issue accept or reject action after the object is highlighted