One
of the most challenging research problem in interactive computer graphics is to
develop the faster and less expensive methods of solid object display.
Introduction to
GKS Primitives !
GKS
(the Graphical Kernel System) is an ANSI and ISO standard. GKS standardizes
two-dimensional graphics functionality at a relatively low level. The primary
purposes of the standard are:
§ To provide for portability of graphics application programs.
§ To aid in the understanding of graphics methods by
application programmers.
To provide guidelines for manufacturers in
describing useful graphics capabilities.
Output
Primitives
A
basic graphic element that can be used to construct a picture. There are four
basic output primitives:
§ Polyline
§ Polymarker
§ Fill Area
§ Text
Polyline
The
GKS function for drawing line segments is called polyline. The polyline
function takes an array of X-Y coordinates and draws line segments connecting
them. The attributes that control the appearance of a polyline are:
§ Linetype: which controls whether the polyline is drawn as a
solid, dashed, dotted, or dash-dotted line
§ Linewidth scale factor: which controls how thick the line
is.
§ Polyline color index: which controls what color the line is.
Polymarkers
The
GKS polymarker function allows you to draw marker symbols centered at
coordinate points that you specify. The attributes that control the appearance
of polymarkers are:
§ Marker: which specifies one of five standardized symmetric
characters to be used for the marker. The five characters are dot, plus,
asterisk, circle, and cross.
§ Marker size scale factor: which controls how large each
marker is (except for the dot marker).
§ Polymarker color index: which specifies what color the
marker is.
Fill
Area
The
GKS fill area function allows you to specify a polygonal shape of an area to be
filled with various interior styles. The attributes that control the appearance
of fill areas are:
§ Fill area interior style: which specifies how the polygonal
area should be filled: with solid colors or various hatch patterns, or with
nothing, that is, a line is drawn to connect the points of the polygon, so you
get only a border.
§ Fill area style index: If the fill area style is hatch, this
index specifies which hatch pattern is to be used: horizontal lines; vertical
lines; left slant lines; right slant lines; horizontal and vertical lines; or
left slant and right slant lines.
§ Fill area color index, which specifies the color of the fill
patterns or solid areas.
Text
The
GKS text function allows you to draw a text string at a specified coordinate
position. The attributes that control the appearance of text are:
§ Text font and precision: which specifies what text font
should be used for the characters and how precisely their representation should
adhere to the settings of the other text attributes.
§ Character expansion factor: which controls the
height-to-width ratio of each plotted character.
§ Character spacing: which specifies how much additional white
space should be inserted between characters in a string.
§ Text color index: which specifies what color the text string
should be.
Segmentation
Segment
is a collection of output primitives that can be manipulated as a unit. In GKS,
segment attributes are visibility, highlighting, detectability, segment
priority and segment transformation.
In
addition to the GKS functions, you may wish to use the segmentation functions
provided in GKS for storing instructions in segments. You may use those
segments in several ways: by inserting them into subsequent pictures; by
translating, rotating, and scaling the segments; and by specifying whether a
segment is visible or not, or whether it is highlighted or not.
You
can
§ Create segment with CREATE SEGMENT command.
§ Close segment with CLOSE SEGMENT command.
§ Delete segment with DELETE SEGMENT command.
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