Character Attribute in computer graphics

Character Attribute in computer graphics

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  PRESENTED BY CHARACTER ATTRIBUTES Mrs.A.AgathaChithra M.Sc.,B.Ed.,M.Phil.,
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  Character Attributes  Theappearance of displayed characters is controlled by attributes such as font, size, color, and orientation.  Attributes can be set both for entire character strings (text) and for individual characters defined as marker symbols.
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  Text Attributes • Firstof all, there is the choice of font (or typeface), which is a set of characters with a particular design style such as New York, Courier, Helvetica, London, 'Times Roman, and various special symbol grou ps. • The characters in a selected font can also be displayed with assorted underlining styles (solid, dotted, double), in boldface, in italics. and in outline or shadow styles.
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  • A particularfont and associated style is selected in a PHIGS progra m by setting an integer code for the text font parameter t f in the fun ction. setTextFont(tf) • Color settings for displayed text are stored in the system attribute lis t and used by the procedures that load character definitions into the f rame buffer. • When a character string is to be displayed, the current color is used t o set pixel values in the frame buffer corresponding to the character shapes and positions
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  • Control oftext color (or intensity) is managed from an application p rogram with setTextColorIndex(tc) • where text color parameter to specifies an allowable color code. • Character size (height) is specified by printers in points, where 1 poi nt=0.035146 cm.
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  • The distancebetween the bottom line and the top line of the characte r body is the same for all characters in a particular size and typeface, but the body width may vary. • Character height is defined as the distance between the baseline and the cap line of characters.
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  • Text sizecan be adjusted without changing the width-to-height ratio of characters with setChatacterHeight(ch) • Parameter ch is assigned a real value greater than 0 to set the coordi nate height of capital letters: the distance between baseline and capli ne in user coordinates.
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  • The widthonly of text can be set with the function setCharacterExpansionFactor(cw) • where the character-width parameter cw is set to a positive real valu e that scales the body width of characters.
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  • Spacing betweencharacters is controlled separately with setCharacterSpacing(cs) • where the character-spacing parameter cs can he assigned any real v alue. The value assigned to cs determines the spacing between chara cter bodies along print lines. • Negative values for cs overlap character bodies; positive values inse rt space to spread out the displayed characters.
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  • The orientationfor a displayed character string is set according to th e direction of the character up vector: • setCharacterUpVector(upvect) • Parameter upvect in this function is assigned two values that specify the x and y vector components. • Text is then displayed so that the orientation of characters from basel ine to capline is in the direction of the up vector.
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  • For example,with upvect = (I, I), the direction of the up vector is 45" and text would be displayed
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  • It isuseful in many applications to be able to arrange character strin gs vertically or horizontally. An attribute parameter for this option is set with the statement setTextPath(tp) • where the text-path parameter tp can be assigned the value: right, lef t, up, or down. • A procedure for implementing this option must transform the charac ter patterns into the specified orientation before transferring them to the frame buffer
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  • Another handyattribute for character strings is alignment. This attri bute specifies how text is to be positioned with respect to the start co ordinates. Alignment attributes are set with setAlignment(h,v) • where parameters h and v control horizontal and vertical alignment. • Horizontal alignment is set by assigning ha value of left, centre, or ri ght. • Vertical alignment is set by assigning v a value of top, cap, half, bas e, or bottom
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  Fig: Alignments ofa Character String
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  • A precisionspecifici~tionf or text display is given with setTextPrecision(tpr) • where text precision parameter tpr is assigned one of the values: strin g, char, or stroke. • The highest-quality text is displayed when the precision parameter is set to the value stroke
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  Marker Attribute • Amarker symbol is a single character that can he displayed in differ ent colors and in different sizes. • We select a particular character to be the marker symbol with setMarkerType(mt) • Where marker type parameter mt is set to an integer code. • Typical codes for marker type are the integers 1 through 5, • Specifying, respectively, a dot (.), a vertical cross (+), an asterisk (*) , a circle (o), and a diagonal cross (X)." Displayed marker types are centered on the marker coordinates.
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  • We setthe maker size with setMakerSizeScaleFactor (ms) • Marker color is specified with setPolymarkerColoulndex (mc) • A selected color code for parameter mc is stored in the current attribu te list and used to display subsequently specified marker primitives.
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  Thank You