Input of graphical data

Input of graphical data

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  S.RAJAPRIYA Assistant Professor ofIT rajapriya@vvvcollege.org
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   Graphics programsuse 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
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   There aresix logical device classification used by PHIGS and GKS. LOCATOR devices STROKE devices STRING devices VALUATOR devices CHOICE devices PICK devices
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   A devicefor 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.
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   To inputa 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
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   Primary physicaldevice used for string input – keyboard.  Used for picture or graph labelling in computer-graphics applications
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   To setthe 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
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   Menus, typicallyused 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.
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   To selecta 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
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   Coordinate-extent testsdo 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
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   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