CD -- CGM Draw Documentation

CD Documentation
A graphics library for fast CGM creation
Follow this link for thelatest version of the CD documentation.
Table of Contents
Credits and license termsWhat‘s newWhat is cd?What else do I need to use cd?How do I get cd?How do I build cd?cd basics: using cd in your programFunction and type reference by categoryUsing cd instead of gdPlease tell us you‘re using cd!
cd was written byG. Edward Johnson at theNational Institute of Standards and Technology. You may use this code for any purpose, but please give us credit. If find cd useful, pleaselet us know. cd software produced by NIST, an agency of the U.S. government, is by statute not subject to copyright in the United States. Recipients of this software assume all responsibilities associated with its operation, modification and maintenance.
Some of this code is from the gd library written by Thomas Boutell. Mr. Boutell did not help with this project, so do not send him questions about cd. Code from gd is clearly marked in the source. Additionally, this document is patterned after the gd documentation, some portions have been copied verbatim. gd is covered by the following license.
gd 1.2 is copyright 1994, 1995, Quest Protein Database Center, Cold Spring Harbor Labs. Permission granted to copy and distribute this work provided that this notice remains intact. Credit for the library must be given to the Quest Protein Database Center, Cold Spring Harbor Labs, in all derived works. This does not affect your ownership of the derived work itself, and the intent is to assure proper credit for Quest, not to interfere with your use of gd. If you have questions, ask. ("Derived works" includes all programs that utilize the library. Credit must be given in user-visible documentation.)
The Quest Protein Database Center is funded under Grant P41-RR02188 by the National Institutes of Health.
Version 1.2
New Text attributes: cdSetTextPath sets the text direction as right, left, up, or down cdSetTextOrient sets the angle of the text
Multiple pictures in a file. Now you can put more than one picture in a cgm file, see cdCgmNewPic for details. Internal changes like using short int‘s in some places so it may take less space in memory when using 16 or 64 bit compilers. New example programs. cdtext to show the new text attributes. cdmulti to show the multiple picture capability.
Version 1.1
Thanks to Wolfgang Glunz who purified it, pointed out some bugs and did the Borland makefile. Switched from using malloc to calloc most cases, solving an off by one error in a function I then eliminated. Added a Makefile for Borland Turbo C++ Fixed a couple of spelling errors, cleared out some dead code, and some other trivial things. Added a new example program cdsimple which walks you through some basics. Added a new function cdPolyLine for when you want lines with more than two points
 
Version 1.0
Basically, everything is new, this is the first release.
cd is a graphics library. It allows your code to quickly draw images complete with lines, arcs, rectangles, polygons, text, and multiple colors. most geometric shapes can be filled or have a hatch pattern as well. The output is a CGM file. If you are unsure of what CGM is, or if CGM is appropriate for your project, see theNIST CGM Homepage.
Every effort has been made to ensure that the generated cgm files conform to the standard, however, if you do not use the library properly, you could generate invalid metafiles that no one is able to read, so be careful.
To use cd, you will need an ANSI C compiler. Any full-ANSI-standard C compiler should be adequate, although those with PCs will need to replace the Makefile with one of their own. The cc compiler released with SunOS 4.1.3 is not an ANSI C compiler. Get gcc, which is freely available. See the Sun-related newsgroups for more information.
You will also want a CGM viewer, if you do not already have one for your system, since you will need a good way to check the results of your work.
You canfetch cd as a gzip‘ed tar file, or you can FTP it directly from zing.ncsl.nist.gov in the subdirectory cgm.
Note: if you have a non-Unix system, you will need to acquire versions of "gunzip" and "tar" suitable for your system. Both have been ported to PC and Mac environments. Consult newsgroups relevant to your particular system.gunzip cd1.2.tar.gztar -xf cd1.2.tarThis will create the directory "cd1.2" beneath the current directory.
 
change to this directory and examine the Makefile, which you may need to change slightly depending on your installation (or more than slightly for a Windows or Mac environment). On UNIX systems the command "make all" will create the cd library and three example programs, cdsimple, cdtest, and color16. If you are using Borland Turbo C++ version 3 (or later I hope) try to make it using makefile.bor
CGM files are always in Network Byte order, Big-Endian systems use this ordering. I wrote this on a Big-Endian machine, but it seems to work on Little-Endian‘s as well. I have Tested cd on Sun‘s, Ultrix, Linux, IRIX, and DOS (Borland). If you get it to run on other systems, drop me a note.
cd lets you create CGM images on the fly. To use cd in your program, include the file cd.h, and link with the libcd.a library produced by "make libcd.a", under Unix. You will need to adapt the makefile for your needs if you are using a non-Unix operating system, but this is very straightforward.
Look at the example programs included in this distribution for examples of using cd. The programs are cdsimple which is a heavily commented program that makes a small cgm. cdtest which makes a cgm with every different kind of shape you can use. It has lines, circles, arcs, ellipses, rectangles, polygons, and text as well as examples for setting the attributes for them. So look at it closely, it is your friend. The other example program, color16 allocates 16 colors using cdImageColor16 (these are the 16 standard Windows colors). Than it draws a rectangle with each of them. These programs are created automatically when you "make all".
TypesImageImage PointerPointPoint Pointer
Image creation, destruction, and savingCreationDestructionSaving
Drawing functionsLinesPolylinesRectanglesCirclesArcsClosed ArcsEllipsesPolygons
Font and text-handling functionsText AttributesThe Font of textThe Color of textThe Height of textThe path text followsThe angle of text
Writing Text
Line, Edge, and Fill attributesLine AttributesLine TypeLine WidthLine Color
Filled Area AttributesInterior StyleFill ColorHatch Index
Exterior Filled Area AttributesEdge TypeEdge WidthEdge ColourEdge Visibility
Color handling functionsAllocate a new colorFind a close matchFind an exact matchNumber of allocated colorsRed portion of colorGreen portion of colorBlue portion of color
Constants
(Type)The data structure in which cd stores images.cdImageCreate returns a pointer to this type, and other functions expect to receive a pointer to this type as their first argument. (Type)A pointer to an image structure.cdImageCreate returns this type, and the other functions expect it as the first argument. you may read the members sx (size of x axis), sy (size of y axis), colorsTotal (total colors allocated), red (red component of colors; an array of 256 integers between 0 and 255), green (green commponent of colors), and blue (blue component of colors). Please do so using the macros provided. Do Not set the members directly from your code, use the functions provided. (Type)Represents a collection of points in the coordinate space of the image; used bycdPolygon and bycdPolyLine.
 
cdPointPtr is defined in cd.h, basically, it is an array of integer pairs p[m].x and p[m].y containing the x and y values respectively. pcnt is the number of points in this array (not the index of the last point, which is pcnt-1). pcnt must be at least 3 for polygons or 2 for polylines.
Declare it with cdPoint points[pcnt] where pcnt is the upper limit of the number of points you wish to have. then fill it in with points[0].x = x0; points[0].y = y0; and the like.
(Type)A pointer to acdPoint structure; passed as an argument tocdPolygon and tocdPolyLine.
(Function)cdImageCreate is called to create images. Invoke cdImageCreate with the x and y dimensions of the desired image. cdImageCreate returns acdImagePtr to the new image, or NULL if unable to allocate the image. The image must eventually be destroyed usingcdImageDestroy (Function)cdImageDestroy is used to free the memory associated with and image. It is important to invoke cdImageDestroy before exiting your program or assigning a new image to acdImagePtr variable. (Function)cdCgmNewPic allows for a single CGM file to contain multiple pictures. If sticky is 0 then all attributes will be reset to their default condition and the color table will be cleared. If sticky is 1 then all attributes and the color table will be carried over to the new picture. NOTE: as of now (version 1.2) the only allowable value for sticky is 0. If you set it to 1, the function will fail. (Function)cdImageCgm outputs the specified image to the specified file in the CGM image format. The file must be open for writing. Under MSDOS, it is important to use "wb" as opposed to simply "w" as the mode when opening the file, and under UNIX there is no penalty for doing so. cdImageCgm does not close the file, your code must do that.
(Function)Graphic Primitive: Polyline; Elem Class 4; Elem ID 1
Returns 1 for success, 0 for failure. cdLine is used to draw a line between two endpoints (x1,y1) and (x2,y2) This line is drawn using the attributes set bycdSetLineAttrib The attributes that may be set areLine Type,Line Width, orLine Color. The endpoints must be within the bounds of the picture. (Function)Graphic Primitive: Polyline; Elem Class 4; Elem ID 1
Returns 1 for success, 0 for failure. cdPolyLine draws a line connecting all the points specified bycdPointPtr. n is the number of points in cdPointPtr, (not the index of the last point, which is n-1). This line is drawn using the attributes set bycdSetLineAttrib The attributes that may be set areLine Type,Line Width, orLine Color. Note that it uses line attributes not edge attributes for drawing the line. The endpoints must be within the bounds of the picture.
 
cdPointPtr is defined in cd.h, basically, it is two arrays of integers p[m].x and p[m].y containing the x and y values respectively. n is the number of points in this array (not the index of the last point, which is n-1). n must be at least 2 (otherwise you really don‘t have much of a line, it is closer to a point.)
(Function)Graphic Primitive: rectangle; Elem Class 4; Elem ID 11
Returns 1 for success, 0 for failure. cdRectangle draws a line which has (x1,y1) as the upper left corner and (x2,y2) as the lower right corner. This rectangle is drawn using the attributes set bycdSetShapeFillAttrib and bycdSetShapeEdgeAttrib. The fill attributes that may be set areFill Style,Fill Color, orFill Hatch. The edge attributes that may be set areEdge Type,Edge Width,Edge Color, orEdge Visibility. Note that it uses Edge attributes not line attributes for drawing the perimeter of the rectangle. The Rectangle must be within the bounds of the picture. (Function)Graphic Primitive: circle; Elem Class 4; Elem ID 12
Returns 1 for success, 0 for failure. cdCircle draws a circle which has center (cx, cy) and radius r. This circle is drawn using the attributes set bycdSetShapeFillAttrib and bycdSetShapeEdgeAttrib. The fill attributes that may be set areFill Style,Fill Color, orFill Hatch. The edge attributes that may be set areEdge Type,Edge Width,Edge Color, orEdge Visibility. Note that it uses Edge attributes not line attributes for drawing the perimeter of the Circle. The Circle must be within the bounds of the picture. (Function)Graphic Primitive: Cicular Arc 3 Point; Elem Class 4; Elem ID 13
Returns 1 for success, 0 for failure. cdArc3Pt draws an arc specified by the given points. (sx,sy) is the start of the arc, (ix,iy) is the middle of the arc, and (ex,ey) is the end of the arc. This arc is drawn using the attributes set bycdSetLineAttrib The attributes that may be set areLine Type,Line Width, orLine Color. Note that it uses Line attributesfor drawing the perimiter of the arc, not Edge attributes likecdArc3PtClose. The Arc must be within the bounds of the picture. (Function)Graphic Primitive: Cicular Arc 3 Point Close; Elem Class 4; Elem ID 14
Returns 1 for success, 0 for failure. cdArc3PtClose draws an arc specified by the given points. (sx,sy) is the start of the arc, (ix,iy) is the middle of the arc, and (ex,ey) is the end of the arc. The arc is closed base on cl. If cl is 0 then pie closure will be used, resulting in a pie shaped slice. if cl is 1 then cord closure will be used and a straight line will be drawn from one endpoint to the other. This arc is drawn using the attributes set bycdSetShapeFillAttrib and bycdSetShapeEdgeAttrib. The fill attributes that may be set areFill Style,Fill Color, orFill Hatch. The edge attributes that may be set areEdge Type,Edge Width,Edge Color, orEdge Visibility. Note that it uses Edge attributes for drawing the perimeter of the arc, not Line attributes likecdArc3Pt. The Arc must be within the bounds of the picture. (Function)Graphic Primitive: Ellipse; Elem Class 4; Elem ID 17
Returns 1 for success, 0 for failure. cdEllipse draws an ellipse specified by the given points. (cx,cy) is the center, (d1x,d1y) is the endpoint of the first conjugate diameter, (d2x, d2y) is the endpoint of the second conjugate diameter. I can‘t really explain this one, if you come up with a good description,mail me. This ellipse is drawn using the attributes set bycdSetShapeFillAttrib and bycdSetShapeEdgeAttrib. The fill attributes that may be set areFill Style,Fill Color, orFill Hatch. The edge attributes that may be set areEdge Type,Edge Width,Edge Color, orEdge Visibility. Note that it uses Edge attributes not line attributes for drawing the perimeter of the Ellipse. The Ellipse must be within the bounds of the picture. (Function)Graphic Primitive: Polygon; Elem Class 4; Elem ID 7
Returns 1 for success, 0 for failure. cdPolygon draws a closed polygon connecting the points specified bycdPointPtr. n is the number of points in cdPointPtr, (not the index of the last point, which is n-1). This polygon is drawn using the attributes set bycdSetShapeFillAttrib and bycdSetShapeEdgeAttrib. The fill attributes that may be set areFill Style,Fill Color, orFill Hatch. The edge attributes that may be set areEdge Type,Edge Width,Edge Color, orEdge Visibility. Note that it uses Edge attributes not line attributes for drawing the perimeter of the polygon. The polygon must be within the bounds of the picture.
 
cdPointPtr is defined in cd.h, basically, it is two arrays of integers p[m].x and p[m].y containing the x and y values respectively. n is the number of points in this array (not the index of the last point, which is n-1). n must be at least 3 (otherwise you really don‘t have much of a polygon, it is closer to a line.)
(Function)Returns 1 for success, 0 for failure. cdSetTextAttrib sets the attributes for text elements. TheFont functions are affected by this. These attributes stay in effect until they are changed, you don‘t have to call this function every time. If you call the function with a value of -1 for any of the attributes they will not be changed. If you call the function with the same value for an attribute as it already has, it will not be changed (so you don‘t have to worry about bloating your CGM with redundant attribute changes.) It calls three functions.cdSetTextFont to set the index into the font table,cdSetTextColor with color to set the forground color of the text, andcdSetTextHeight with height to set the height of the text. You may also call any of the three functions individually if you like. (Function)Graphic Primitive: Text; Elem Class 4; Elem ID 4
Returns 1 for success, 0 for failure. cdText puts a string of text ts starting at position (x,y) The Text is drawn using the attributes set withcdSetTextAttrib. The attributes that may be set are:cdSetTextFont,cdSetTextColor, orcdSetTextHeight. The point where the text starts must be within the bounds of the picture. (Function)Attribute: Text Path; Elem Class 5; Elem ID 17
Returns 1 for success, 0 for failure. sets the path of the text to tpath. tpath is an integer with one of the following values 0 for right 1 for left 2 for up 3 for down
These are all relative to the charater base vector and up vector. If you haven‘t changed them (withcdSetTextOrient then the direction of the text will be right to left for 0, left to right for 1, bottom to top for 2, and top to bottom for 3. Each individual letter will still be facing in the normal direction. If you want to rotate the text usecdSetTextOrient.
 
Things get more interesting if you usecdSetTextOrient with this function. A more exact definition of tpath is 0 right -- the direction of the character base vector 1 left -- 180 degrees from the direction of the character base vector 2 up -- the direction of the character up vector 3 down -- 180 degrees from the direction of the character up vector
 
(Function)Attribute: Character Orientation; Elem Class 5; Elem ID 16
Returns 1 for success, 0 for failure. (xbase,ybase) is the run and the rise of the line that the text is written along. For regular text that is rotated, set xup = -ybase and yup = xbase. Setting it to something different will result in skewed text (which may be what you want.) Text written from bottom to top at a 90 degree angle would have the following parameters xup=-1, yup=0, xbase=0, ybase=1
 
This function adds the Orientation to the metafile every time. It does not interpert an attribute value of -1 as no change like many functions do, although if you put in the same numbers it won‘t re-add it to the meta file.
(Function)Attribute: Text Font Index; Elem Class 5; Elem ID 10
Returns 1 for success, 0 for failure. Sets the font index to font. It is an index into the font table, the possible values are: 1 for Times 2 for Times Bold 3 for Times Italic 4 for Times Bold Italic 5 for Helvetica 6 for Helvetica Bold 7 for Helvetica Italic 8 for Helvetica Bold Italic
font must be one of these values or the function will fail. SeecdSetTextAttrib for more information on this and related functions. (Function)Attribute: Text Colour; Elem Class 5; Elem ID 14
Returns 1 for success, 0 for failure. Sets the foreground color of text to color. This should be an integer which is an index into the color table that you have previously allocated. SeecdSetTextAttrib for more information on this and related functions. (Function)Attribute: Character Height; Elem Class 5; Elem ID 15
Returns 1 for success, 0 for failure. height is an integer for the height of the text you are displaying. Bigger numbers make larger text. The size of the text is dependent on the size of the picture. SeecdSetTextAttrib for more information on this and related functions.
(Function)Returns 1 for success, 0 for failure. cdSetLineAttrib sets the attributes for lines and non-closed area elements. Thedrawing functions affected areLinesArcs
These attributes stay in effect until they are changed, you don‘t have to call this function every time. If you call the function with a value of -1 for any of the attributes they will not be changed. If you call the function with the same value for an attribute as it already has, it will not be changed (so you don‘t have to worry about bloating your CGM with redundant attribute changes.) It calls three functions.cdSetLineType with lntype to set the line type (solid, dashed, etc),cdSetLineWidth with lnwidth to set how wide the line is, andcdSetLineColor to set the color of the line. You may also call any of the three functions individually if you like. (Function)Returns 1 for success, 0 for failure. cdSetShapeFillAttrib sets the attributes for the interior of closed area elements. Thedrawing functionsaffected areRectanglesCirclesClosed ArcsEllipses
These attributes stay in effect until they are changed, you don‘t have to call this function every time. If you call the function with a value of -1 for any of the attributes they will not be changed. If you call the function with the same value for an attribute as it already has, it will not be changed (so you don‘t have to worry about bloating your CGM with repetitive attribute changes. It calls three functions.cdSetFillStyle with instyle to set the interior style (solid, hatch, empty),cdSetFillColor with incolor to set the interior color (used if instyle is solid or hatch), andcdSetFillHatch with inhatch to set the hatch style (hor lines, vert lines, crosshatch, etc) (used if instyle is hatch). You may also call any of the three functions individually if you like. (Function)Returns 1 for success, 0 for failure. cdSetShapeEdgeAttrib sets the attributes for the perimeter of Filled area elements. It might seem logical to use the line attributes instead, but that is not the case. Thedrawing functionsaffected areRectanglesCirclesClosed ArcsEllipses
These attributes stay in effect until they are changed, you don‘t have to call this function every time. If you call the function with a value of -1 for any of the attributes they will not be changed. If you call the function with the same value for an attribute as it already has, it will not be changed (so you don‘t have to worry about bloating your CGM with redundant attribute changes.) cdSetShapeEdgeAttrib calls three functions.cdSetEdgeType with edtype to set the edge type (solid, dashed, etc),cdSetEdgeWidth with edwidth to set the width of the line around the perimeter,cdSetEdgeColor with edcolor to set the color of the line around the perimeter, andcdSetEdgeVis with edvis to determine if the line around the perimeter is visible. You may also call any of the three functions individually if you like. (Function)Attribute: Line Type; Elem Class 5; Elem ID 2
Returns 1 for success, 0 for failure. lntype is the line type which is an integer with possible values of: 1 for a solid line 2 for a dashed line 3 for a dotted line 4 for a dash-dot line 5 for a dash-dot-dot line
lntype must be one of these values or the function will fail. SeecdSetLineAttrib for more information on this and related functions. (Function)Attribute: Line Width; Elem Class 5; Elem ID 3
Returns 1 for success, 0 for failure. lnwidth is an integer giving the width of lines. With an image of height Y with line width 1 the displayed width will be 1/Y%. As an example, if you image is x=5, y=10, and you set line width = 1, and draw a vertical line, the resulting line will cover 20% of horizontal area. (I think anyway). SeecdSetLineAttrib for more information on this and related functions. (Function)Attribute: Line Colour; Elem Class 5; Elem ID 4
Returns 1 for success, 0 for failure. Sets the line color to lncolor. This should be an integer which is an index into the color table that you have previously allocated. SeecdSetLineAttrib for more information on this and related functions. (Function)Attribute: Interior Style; Elem Class 5; Elem ID 22
Returns 1 for success, 0 for failure. Sets the style of the interior of filled area elements. instyle is the interior style which is an integer with possible values of: 0 for hollow. No filling, but the boundary (bounding line) of the filled area is drawn using the fill colour currently selected. The boundary of a "hollow" filled area is considered to be the representation of the interior. The boundary is distinct from the edge, and is drawn only for "hollow" filled areas 1 for solid. Fill the interior using the fill colour currently selected 3 for hatch. Fill the interior using the fill colour and hatch index currently selected. 4 for empty. No filling is done and no boundary is drawn, i.e., nothing is done to represent the interior. The only potentially visible component of an "empty" filled area is the edge, subject to EDGE VISIBILITY and other edge attributes.
instyle must be one of these values or the function will fail. So, basically, if you want an interior which is transparent and you can see what is underneath it, use "empty" otherwise fill it in with a hatch or solid color. SeecdSetShapeFillAttrib for more information on this and related functions. (Function)Attribute: Fill Colour; Elem Class 5; Elem ID 23
Returns 1 for success, 0 for failure. Sets the fill color to incolor. This should be an integer which is an index into the color table that you have previously allocated. SeecdSetShapeFillAttrib for more information on this and related functions. (Function)Attribute: Hatch Index; Elem Class 5; Elem ID 24
Returns 1 for success, 0 for failure. Sets the hatch pattern for the interior of filled-area elements to inhatch. Thefill style must be set to hatch for this to have an effect. the value for inhatch is the hatch style, which is an integer with possible values of: 1 for horizontal lines 2 for vertcal lines 3 for positive slope parallel lines 4 for negative slope parallel lines 5 for horizontal/vertical crosshatch 6 for positive/negative slope crosshatch
lntype must be one of these values or the function will fail. SeecdSetShapeFillAttrib for more information on this and related functions. (Function)Attribute: Edge Type; Elem Class 5; Elem ID 27
Returns 1 for success, 0 for failure. edtype is the edge type which is an integer with possible values of: 1 for a solid line 2 for a dashed line 3 for a dotted line 4 for a dash-dot line 5 for a dash-dot-dot line
edtype must be one of these values or the function will fail. SeecdSetShapeEdgeAttrib for more information on this and related functions. (Function)Attribute: Edge Width; Elem Class 5; Elem ID 28
Returns 1 for success, 0 for failure. edwidth is an integer giving the width of the perimeter lines. With an image of height X with line width 1 the displayed width will be 1/X%. As an example, if you image is x=5, y=10, and you set line width = 1, and draw a vertical line, the resulting line will cover 20% of horizontal area. (I think anyway). SeecdSetShapeEdgeAttrib for more information on this and related functions. (Function)Attribute: Edge Color; Elem Class 5; Elem ID 29
Returns 1 for success, 0 for failure. Sets the color of the perimeter lines to edcolor. This should be an integer which is an index into the color table that you have previously allocated. SeecdSetShapeEdgeAttrib for more information on this and related functions. (Function)Attribute: Edge Visibility; Elem Class 5; Elem ID 30
Returns 1 for success, 0 for failure. edvis is an integer that can have one of the following values. 0 for invisible edges 1 for visible edges
If you set the edge visibility to off (invisible edges) than you will not see the edges, regardless of what other edge attributes are set. The other attributes will still be set and turning the edge visibility to on will make edges using the current edge styles. SeecdSetShapeEdgeAttrib for more information on this and related functions.
(Function)cdImageColorAllocate finds the first available color index in the image specified, sets its RGB values to those requested (255 is the maximum for each), and returns the index of the new color table entry. When creating a new image, the first time you invoke this function, you are setting the background color for that image.
In the event that allcdMaxColors colors (256) have been allocated already, cdImageColorAllocate will return -1 to indicate failure, otherwise it will return the index into the color table allocated. (Note that most functions return 0 on failure, but 0 is a valid color table entry.)
cdImageColorAllocate does not check for existing colors that match your request, you might want to usecdImageColorExact prior to calling this function to keep from defining multiple indexes with the same color. If color alocation fails, usecdImageColorClosest to find the nearest matching color.
(Function)cdImageColorClosest searches the colors which have been defined thus far in the image specified and returns the index of the color with RGB values closest to those of the request. (Closeness is determined by Euclidian distance, which is used to determine the distance in three-dimensional color space between colors.)
If no colors have yet been allocated in the image, gdImageColorClosest returns -1.
This function is most useful as a backup method for choosing a drawing color when an image already containscdMaxColors (256) colors and no more can be allocated. SeecdImageColorExact for a method of locating exact matches only.
(Function)cdImageColorExact searches the colors which have been defined thus far in the image specified and returns the index of the first color with RGB values which exactly match those of the request. If no allocated color matches the request precisely, cdImageColorExact returns -1. SeecdImageColorClosest for a way to find the color closest to the color requested. (Macro)cdImageColorsTotal is a macro which returns the number of colors currently allocated in the image. Use this macro to obtain this information; do not access the structure directly. (Macro)cdImageColorRed is a macro which returns the red portion of the specified color in the image. Use this macro to obtain this information; do not access the structure directly. (Macro)cdImageColorGreen is a macro which returns the green portion of the specified color in the image. Use this macro to obtain this information; do not access the structure directly. (Macro)cdImageColorBlue is a macro which returns the green portion of the specified color in the image. Use this macro to obtain this information; do not access the structure directly.
ConstantcdMaxColors is the maximum number of colors that can be allocated in a CGM picture. the CGM standard allows for many different ways of allocating colors, but I have chosen to limit this library to 8 bit indexed color. This means the maximum value of this is 256. If you really wanted to you could make it smaller though it would not have an effect on the resulting file size. ConstantWhen you create an image, a buffer is allocated to hold the drawing commands. This is the initial size of the buffer in bytes. When it is filled, the size gets increased byCDGROWLISTSIZE. If you know you are going to be working with very small CGM‘s then make this a small number. If you know your CGM‘s will be large increase this number. If CDSTARTLISTSIZE is smaller than the header information than it will have to grow before you do anything. I wouldn‘t make it smaller than 1024. Try to make it as large as the average picture you make. ConstantWhen you create an image, a buffer is allocated to hold the drawing commands. When the buffer is filled, the size is increased by the amount given in CDGROWLISTSIZE (in bytes). If you know that most of the CGM‘s you create will be near the size ofCDSTARTLISTSIZE than make this number small. If there is lots of variablility in the size of your CGM‘s, make this number large. If CDGROWLISTSIZE is larger than CDSTARTLISTSIZE, you should probably increase the value of CDSTARTLISTSIZE. If CDGROWLISTSIZE is smaller than the largest CGM element you create than it will be growing alot, so I wouldn‘t make it smaller than about 1024.
CD was designed to be easy to use instead of gd (or with gd, if you want to be able to produce both). However, There are significate differences between the way CGM handles attributes versus the way gd does. In particular, gd requires you to put the line color in the function call to draw lines, CD does not, Color, like the other attributes only need to be set when they are changed. I recomend that you read over the documentation of both to see what the differences are, and make appropriate changes to your code. If you really want to make as few changes as possible to your code, I have provided two functions to help you. cdImageLine takes the same parameters as gdImageLine and will draw a solid line of the color specified. cdImageRectangle draws a hollow rectangle with solid edges of the color specified. I did this by drawing four lines, so it is not a true rectangle. Again, I recomend you use cdLine and cdRectangle instead of these, but they are there if you want them.
When you contact us and let us know you are using cd, you help us justify the time spent in maintaining and improving it. So please let us know. If the results are publicly visible on the web, a URL is a wonderful thing to receive, but if it‘s not a publicly visible project, a simple note is just as welcome.
G. Edward Johnson
lorax@nist.gov