Converter: How the Position of Screens Is Converted

• Microsoft Visual FoxPro for Windows, version 3.0

SUMMARY

This article addresses the issue of positioning converted screens. It explains how window position is calculated in FoxPro version 2.x for Windows and in Visual FoxPro. It also describes how the converter converts screen position. The source code to the CONVERT.APP application is included with the Professional Edition of Visual FoxPro, and is installed in the TOOLS\CONVERT directory.

MORE INFORMATION

FoxPro version 2.x for Windows uses foxels to calculate window and object location. A foxel is a unit of measure unique to FoxPro that is equivalent to the average height and width of a character. In FoxPro versions 2.x for Windows, a window position is based on the font of its container. In other words, if a user window is defined on the desktop, the font of the main FoxPro window determines the top and left position of the screen. Developers often place a MODIFY WINDOW SCREEN FONT <fontname>,<fontsize> statement in the Setup code of a FoxPro version 2.x screen to ensure that windows are consistently displayed at the same location on different systems.

A screen added to a FoxPro version 2.x project can be positioned by using the Arrange button. The window's coordinates are saved in foxels in the Project Manager (ARRANGED field of the PJX table). The information relative to the position of the window is not stored anywhere if the screen is not included in a project.

A Visual FoxPro form can use pixels or foxels. A pixel is the smallest element that can be displayed on a screen. It is resolution dependent but is not affected by font information.

Visual FoxPro provides an application (CONVERT.APP) that converts FoxPro 2.x projects to a Visual FoxPro format. The converter dialog is displayed when you open a FoxPro version 2.x project in Visual FoxPro. Screen sets are converted to form sets, and each screen contained in a screen set is converted to a form. The SCALEMODE property of a converted form is set to 3- Pixels.

During the conversion process, CONVERT.APP converts the window position from foxels to pixels. The calculation is defined in the AddPos method of the FP25FORM class in the CONVERT.PRG file. CONVERT.APP uses the font of the desktop in the current Visual FoxPro session as a basis for the conversion.

For example, if the desktop font is MSSansSerif 10, the converter uses the fontmetrics of MSSansSerif 10 to convert the position of the form window. On the other hand, if the desktop font is MSSansSerif 12, MSSansSerif 12 is the basis for the conversion from foxel to pixel, and the resulting window appears at a lower position than it was previously located.

Therefore, to ensure that windows are located at the same absolute position in a converted screen, verify that the font of the main FoxPro window is the same as the one used by FoxPro version 2.6 screens.

NOTE: When the SCALEMODE property of a form is set to 0-Foxels, the window position is based on the font it uses. As opposed to windows defined with a DEFINE WINDOW command used in FoxPro version 2.x screen definition, the top and left positions of a Visual FoxPro form are not set by the font of the container window. Thus, in Visual FoxPro, the MODIFY WINDOW SCREEN FONT <FontName> command does not alter the position of a form.

The following example code illustrates the fact that the position of a window is based on its font:

   omyform1=CREATEOBJECT('myform')
   omyform1.show

   oMyform2=CREATEOBJECT('myform2')
   omyform2.show


   suspend

   DEFINE CLASS MyForm2 AS Form
      caption = "Arial, 18"
      scalemode = 0
      fontname="Arial"
      fontsize=18
      top = 1
      left = 1
      height = 10
      width = 20
   ENDDEFINE

   DEFINE CLASS MyForm AS Form
      caption= "Arial,10"
      scalemode = 0
      fontname="Arial"
      fontsize=10
      top = 1
      left = 1
      height = 10
      width = 20
   ENDDEFINE