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A multiple-resolution display driver provides the code and resources needed
to support all resolutions of a given display device. In previous versions
of Windows, separate display drivers were required for each resolution. In
Windows 3.1, a single display driver can handle all resolutions.
 
A multiple-resolution driver must provide the following:
 
♦  GetDriverResourceID function
 
♦  Icons and cursors for each supported resolution
 
♦  Installation information
 
Resources and Resource Mapping
 
In many cases, the only difference for the driver between the device
resolutions is the size of the resources and the horizontal and vertical
dimensions. A driver can support multiple resolutions as long as it can
determine which resolution Windows expects it to use.
 
To support multiple resolutions in a single display driver, Windows checks
for the GetDriverResourceID function in the driver and calls it before
loading the driver's resources and dimensions. This gives the driver a
chance to check the SYSTEM.INI file using the GetPrivateProfileInt
(KERNEL.127) or GetPrivateProfileString (KERNEL.128) functions for
information specifying the desired resolution. The GetDriverResourceID
function can then map the request resource identifier to the identifier of
the corresponding resource for the desired resolution. In this way, the
driver makes sure Windows loads the appropriate resources for the resolution
to be used.
 
When Windows calls the GetDriverResourceID function, the driver should at
least check for the aspect entry in the [Boot.description] section of the
SYSTEM.INI file. This entry specifies the resolution (in dots-per-inch) of
the display. Drivers use this value to determine which fonts to use as well
as to determine other resource that depend on the number of dots-per-inch
the display generates.
 
Display drivers that support multiple resolutions must export the
GetDriverResourceID function and provide a set of appropriate resources for
each resolution.
 
Installation Information
 
Users select the desired resolution for the display using the Setup program.
To display each screen resolution, Setup checks the [Display] section in the
SETUP.INF or OEMSETUP.INF file. There must be one line for each resolution.
For example, if a video adapter named "ZGA" has three resolutions (640x480,
800x600, and 1024x768), the [Display] section should look something like
this:
 
[display]
zga1=1:zga.drv,"ZGA(640x480)","100,96,96",3:zgacolor.2gr,... ,zgalo
zga2=1:zga.drv,"ZGA(800x600)","100,96,96",3:zgacolor.2gr,... ,zgamed
zga3=1:zga.drv,"ZGA(1024x768)","100,120,120",3:zgacolor.2gr,... ,zgahi
 
Setup installs the same driver (ZGA.DRV), grabbers, virtual-display device,
and other related components. However, the last field in the line specifies
an additional section in the SETUP.INF or OEMSETUP.INF file that contains
resolution-specific information.
 
The resolution-specific information allows Windows Setup to copy files and
write profile data for later use by the display driver. Setup can write the
information to the SYSTEM.INI file in the section and format the driver
understands. When a display driver is initialized, it can use the Windows
functions GetPrivateProfileInt or GetPrivateProfileString to read the
user-specified screen resolution from the appropriate section of SYSTEM.INI.
This will let the driver decide what resource ID to return to Windows by the
GetDriverResourceID function.
 
The following examples show how resolution-specific information sections
might look in the SETUP.INF or OEMSETUP.INF file:
 
[zgalo]
4:zgalo.dll,0:system,,,,
 
[zgamed]
,,system.ini,zga.drv,,"ZGAres=800x600"
 
[zgahi]
4:zgahi.dll,0:system,system.ini,zga.drv,"ZGAres=800x600","ZGAMode=Hi"
 
For more information about the resolution-specific information sections, see
the ◄[Display]► section.
 
 
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