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4D Graphics
Volume Number:7
Issue Number:2
Column Tag:Database Corner

Related Info: Quickdraw

4th Dimension Graphics

By Haven C. Sweet, Orlando, FL

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

Graphics Output in Fourth Dimension.

Haven Sweet is a Professor of Biology at the University of Central Florida. He has been interested in using the Macintosh for a variety of educational purposes, and has tried to incorporate the computer into an academic laboratory setting. He has developed several classroom exercises using 4th Dimension.


Although Fourth Dimension (4D) is not a programming language, I prefer to use it for most of my projects since it vastly simplifies programming and managing complex data. However, I recently discovered a very unfortunate limitation of Fourth Dimension; it is unable to draw on the screen using tool box calls.

The Problem

After creating a large data base of organisms with 4D, I added calculations for a cluster analysis to elucidate their possible relationships. When I wanted to present the final results in a dendrogram (Figure 1), I discovered there was no simple mechanism for drawing on the screen or printing text at variable locations.

Figure 1. A sample clustering output, showing the similarity of four different records in the data base. The figure was drawn on an output layout which only contained the buttons.

I would have to write the entire graphics routine in Pascal, compile it as an external procedure, and create external areas within my program. Not being proficient with MPW, I was hesitant to attempt writing anything which would require debugging by switching from MPW to Ext. Mover to 4D to MPW etc. Hoping version 2 would provide direct toolbox routines such as MoveTo(xStart,yStart), LineTo(xEnd,yEnd) and Writeln(Message), I found that Acius had no such plans.

The Solution

Facing the tedium of learning MPW and Pascal, I hit upon a much simpler solution; I created four external units which provide equivalent procedures for moving the pen, drawing a line, writing text at any location on the screen, and defining both pen and text characteristics. Then, using a blank layout screen, I wrote the graphics routines in the layout procedure and invoked these procedures. Although the graphics output is quite slow, it is more than adequate for the occasional presentation of simple data.

The “pseudo toolbox” routines can be as short or long as needed, but each must be compiled separately and given a name different from the toolbox routine. While I toyed with putting a “4D” before the name of every toolbox call, I decided to combine several I need into a single procedure. So, when text must appear at variable locations on the screen, instead of using MoveTo(xStart;yStart); Writeln(message), the new procedure is WriteAt(xStart;yStart;Message). Likewise, when a line must be drawn, instead of using MoveTo and LineTo, they were combined into DrawLine(xStart;yStart;xEnd;yEnd) which defines the start and end of the line. To alter the text or pen’s characteristics, I adopted the syntax used in ZBasic to produce Pen(xSize;ySize;visible;PenMode) and Text(font;point size;mode). Because variables are used, the procedures can use data either stored in the database or generated from it to draw appropriate lines.

These procedures were written in Pascal and compiled as units which can be moved using 4D External Mover into either the resource of a 4D program or the Proc.Ext. The units are quite small, taking under 600 bytes for all four routines. Once installed, the procedures can be called from within the program in the same manner as any global procedure.

The Output Screen

The next problem was to provide a blank screen on which the results could be written, as well as to find the best way to call the function. My solution was to create a dummy data file with all the drawing done in the output layout procedure. However, there must be exactly one record in the file; if the file is empty, the layout screen never appears, while if there are more than one record in the selection, the drawing procedure is executed for each record. Although it is possible to create a set with only one record in it, it is simpler to create a file named “Blank” which contains only one field, “Dummy”. Then, with the User mode, add one record to the file. An empty layout screen must be created for each different graphics screen.

The layout forms in the file “Blank” should have the three markers Header, Detail, and Break positioned at the very top of the page. If no buttons are to appear in the form, the Footer should also should be placed at the top; otherwise, it should be just far enough down to accomidate the buttons (Figure 2).

Figure 2. The appearance of the layout screen on which the drawing or text placement will be done. Note that the markers for Header, Detail and Break are all at the top of the page.

Although other line positions may work (including using the default positioning of the lines), having them at the top is more reliable since unusual things may occur with some positions. For example, if Break or Header are below the window’s margin, nothing will be drawn; if the Detail line is below the window, then the image is drawn and immediately erased; if space remains between the Header and Detail, clicking on the area permits the user to double click the region and jump to the data input mode. Thus, since the user may resize the window, it is safest to prevent anomalies by placing the lines at the top.

The Procedures’ Syntax

The drawing procedures should only be executed in the BEFORE phase, and should use the following formats:

Pen([xSize] [; [YSize]; [Visible]; [Pen Mode]] )

XSize is the horizontal width of the line in pixels.

YSize is the vertical width of the line in pixels. If omitted or set to zero, the xSize value is used for ySize.

Visible is set to one if the line is to be seen or zero if it is invisible.

Pen Mode uses the following;

0 or 8 Pattern COPY

1 or 9 Pattern OR

2 or 10 Pattern XOR

3 or 11 Pattern BIC

4 or 12 Not pattern COPY

5 or 13 Not pattern OR

6 or 14 Not pattern XOR

7 or 15 Not Pattern BIC

All values are optional. A call to Pen with no parameters resets the normal pen (1 by 1 pixel, visible in the copy mode). Partial parameters may also be used. For example, Pen(3;3;1;8) would produce the same effect as Pen(3) or Pen(3;3)-- that is, a visible pen, 3 by 3 pixels in the copy mode. Although ZBasic also includes the possibility of altering the pen pattern, I did not include it in these routines.

Text( [Font] [; [Point size] ; [Face] ; [Mode]] )

Font codes include;

0 System font

1 Application font

2 New York 20 Times

3 Geneva 21 Helvetica

4 Monaco 22 Courier

5 Venice 23 Symbol

11 Cairo 24 Taliesin

Point size can range from 1 through 127

Face codes are; Mode uses the following;

0 Plain 0 or 8 Pattern COPY

1 Bold 1 or 9 Pattern OR

2 Italic 3 or 11 Pattern BIC

4 Underlined 2 or 10 Pattern XOR

8 Outlined 4 or 12 Not pattern COPY

16 Shadow 5 or 13 Not pattern OR

32 Condensed 6 or 14 Not pattern XOR

64 Extended 7 or 15 Not Pattern BIC

Combinations would be the sum of each face; i.e., bold italic text would have a code of 3.

All values are optional; if omitted, the result is 12 point, plain system font in the copy mode. Both Text(22;10;3;0) and Text(22;10;3) define text as 10 point Courier, italic and bold, which is in the COPY mode.

DrawLine( xStart; yStart; xEnd; yEnd)

This procedure draws a line, with the characteristics defined in the Pen procedure, which begins at a point xStart, yStart, and extends to the point xEnd, yEnd. For example DrawLine(1;1;200;1) would draw a line across the top of the screen.

WriteAt( xStart; yStart; Message)

This procedure writes any text stored in Message beginning at a point xStart, yStart. For example, WriteAt(10;YPos;”The results follow”) would print the text 10 pixels from the left edge and YPos pixels from the top.


The following procedures are designed to draw a line on the screen and to place text near its origin. In this example, the coordinates of the line are entered by the user in a dialog box, but they could have been derived from data in the file.

‘ global procedure Draw a line
ALL RECORDS([Blank]) ‘ this file has one record
 ‘ ask for characteristics of line and text
DIALOG(“Dialog box”)
If (OK=1)|(b1=1)
     INPUT LAYOUT(“Blank-line”)
     OUTPUT LAYOUT(“Blank-line”)
End if 
‘Layout procedure Blank-line
If (Before)
  PenMode:=8   ‘Pattern copy  
 ‘ pen size entered by user
  Pen (xSize;Ysize;visible;PenMode)
 ‘ start and end positions entered by user
  DrawLine (h1;v1;h2;v2)
 ‘ Face entered by user
  Text (0;12;Face;0) ‘ font,point size,style,mode
  WriteAt ((h1+20);(v1+20);”This is where the line begins.”)
End if 

The Units

The Pascal versions of the four procedures are followed by one annoted example of the MPW commands needed to compile each into a unit. This method of directly creating units was devised by Jud Spencer of After Hours Software, and was distributed by Acius as Technical Note #150, March, 1989.

Unit Pen;
 Procedure  PenSet(var Xsize,Ysize,visible, Mode: Integer);
Procedure PenSet(var Xsize,Ysize,visible, Mode: Integer);
 if (Xsize>0) then
 {its OK}
 if (Ysize>0) then
 {its OK}
 if (visible=0) then
 if (Mode>=0) and (Mode<8) then
 Mode:=Mode+8; {correct if wrong mode range used}
 if (Mode>7) and (Mode<16) then
Unit DrawLine;
 Procedure DrawALine(var h1,v1,h2,v2: Integer);
 Procedure DrawALine(var h1,v1,h2,v2: Integer);
Unit Text;
 Procedure TextSet(var font,point,StyleNum,mode: Integer);
 Procedure TextSet(var font,point,StyleNum,mode: Integer);
 if (font>0) then
 if (point>0) and (point<128) then
 if (mode>7) and (mode<16) then
 mode:=mode-8; {correct if wrong mode range used}
 if (mode>=0) and (mode<8) then
 if (StyleNum>0) and (StyleNum<128) then
 end; {procedure}
Unit WriteAt;
 Procedure WriteItAt(var h1,v1:Integer;var s: Str255);   IMPLEMENTATION
 Procedure WriteItAt(var h1,v1:Integer;var s: Str255);

Workshop Commands

MPW worksheet commands for the WriteAt procedure are described below. Set the correct directory, then replace or correct all the items noted below as each different unit is compiled and linked.

Pascal WriteAt.p
#      Fix ^     Use unit’s name
Link -w -p WriteAt.p.o 
#             Fix ^    Use unit’s name
“{Libraries}”Runtime.o 
“{Libraries}”Interface.o 
“{PLibraries}”PasLib.o 
#    Fix ^    use ALL CAPS with the procedure’s name (not the Unit’s)
-rt 4DEX=16114 
#Fix ^ be sure 4D is name of 4th Dimension, or change it here
-sg Main2 
-sn “Main2=WriteAt(&I;&I;&S)” 
#      Fix ^         Fix ^  with proper variable list, where I=integer, 
-o Proc.Ext(WriteAt)
#          Fix ^      with proper unit name


Although some labor is required to initially write and compile the graphics external procedures, it only needs to be done once. After being installed in the Proc.Ext, a 4th Dimension database can access the procedures with minimal effort. Unfortunately, describing the process makes it sound much more difficult than it actually is.


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