DOCUMENT:Q74044  16-JUN-1999  [win16sdk]
TITLE   :INFO: Logical and Physical Coordinate Relationship
PRODUCT :Microsoft Windows Software Development Kit
PROD/VER:WINDOWS:3.1
OPER/SYS:
KEYWORDS:kbSDKWin32 kb32bitOnly

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3.00 3.10
WINDOWS
kbprg

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The information in this article applies to:

 - Microsoft Windows Software Development Kit (SDK) 3.1 
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SUMMARY
=======

Windows is designed to use a logical coordinate system when doing many of its
graphics operations. Many of the Windows functions take logical units as
parameters. Windows translates these units to physical device units based on the
mapping mode of the device, window origin, window extents, viewport origin, and
viewport extents.

This article discusses the relationship between logical and physical coordinates.

MORE INFORMATION
================

The default mapping mode for a device context (DC) is the MM_TEXT mode. The
point (0,0) is the origin of the logical and physical coordinate systems in this
mode. It also has a 1 to 1 mapping ratio of logical to physical device units.

The programmer can change the mapping mode of a DC by using the SetMapMode()
function.

The following six mapping modes have predefined logical to physical mapping
ratios:

 - MM_TEXT

 - MM_LOENGLISH

 - MM_HIENGLISH

 - MM_LOMETRIC

 - MM_HIMETRIC

 - MM_TWIPS

The following two mapping modes can be set to have user defined ratios of logical
to physical units:

 - MM_ANISOTROPIC

 - MM_ISOTROPIC

In the last two modes, coordinates are transformed from logical to physical and
vice versa based on the current window and viewport extents in the DC. The
functions SetWindowExt() and SetViewportExt() allow an application to set the
window and viewport extents. These functions should only be used in the
MM_ANISOTROPIC and MM_ISOTROPIC mapping modes because they are the only ones in
which the application can define the mapping ratio.

The formulae used to convert to and from the different coordinate systems are
documented in section 2.5.3, page 2-18, in the "Microsoft Windows Software
Development Kit Reference Volume 1" for version 3.0.

REFERENCES
==========

For more information about the relationship between the logical and physical
planes, refer to the following:

"Microsoft Windows Software Development Kit Reference Volume 1" version 3.0,
section 2.5 "Mapping Functions," pages 2-15 through 2-20.

"Programming Windows," first edition, by Charles Petzold Chapter 12, pages
520-540.

"Programming Windows," second edition, by Charles Petzold Chapter 11, pages
517-539.

"Peter Norton's Windows 3.0 Power Programming Techniques," by Peter Norton and
Paul Yao, Chapter 20, c. 1990, Bantam Books.

Additional query words: 3.00 3.10

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Keywords          : kbSDKWin32 kb32bitOnly 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1
Issue type        : kbinfo

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