Macintosh: Determining Video Card Status via Software (1 of 2)

Refer to the QuickDraw chapters of "Inside Macintosh, Volume V." Page 124
documents a function called "GetMainDevice". This function returns a
GDHandle (Graphics Device Handle). This handle has the information you
want. Here is its description (page 119):

TYPE
GDHandle = ^GDPtr;
GDPtr = ^GDevice;
GDevice = RECORD
gdRefNum: INTEGER;
gdID: INTEGER;
gdType: INTEGER;
gdITable: ITabHandle;
gdResPref: INTEGER;
gdSearchProc: SProcHndl;
gdCompProc: CProcHndl;
gdFlags: INTEGER;
gdPMap: PixMapHandle;
gdRefCon: LONGINT;
gdNextGD: GDHandle;
gdRect: Rect;
gdMode: LONGINT;
gdCCBytes: INTEGER;
gdCCDepth: INTEGER;
gdCCXData: Handle;
gdCCXMask: Handle;
gdReserved: LONGINT;
END;

The field in the above Pascal record with is the "gdPMap" field. The "gdPMap"
field contains a PixMapHandle. Here is a description of the handle (pages 52
and 53):

TYPE
PixMapHandle = ^PixMapPtr;
PixMapPtr = ^PixMap;
PixMap = RECORD
baseAddr: Ptr;
rowBytes: INTEGER;
bounds: Rect;
pmVersion: INTEGER;
packType: INTEGER;
packSize: LONGINT;
hRes: Fixed;
vRes: Fixed;
pixelType: INTEGER;
pixelSize: INTEGER;
cmpCount: INTEGER;
cmpSize: INTEGER;
planeBytes: LONGINT;
pmTable: CTabHandle;
pmReserved: LONGINT;
END;

This "PixMap" record has a field called "pixelSize" that contains the current
depth, in bits, of the pixels for the graphic device.

The Pascal code to retrieve this information looks something like this:

PROCEDURE GetBitsPerPixel;

VAR
mainDevice: GDHandle;
theDepth: INTEGER;

BEGIN
mainDevice := GetMainDevice;
theDepth := mainDevice^^.gdPMap^^.pixelSize;
END;

If more than one video card is installed in the system, and you need to know
what the bits per pixel setting is on all devices, not just on the main device,
try the following functions (page 124):

GetDeviceList
GetNextDevice

Here is a sample procedure that shows how to use them:

PROCEDURE GetGraphicDevs;

VAR
DeviceList: ARRAY[1..6] OF GDHandle;
theDepthList: ARRAY[1..6] OF INTEGER;
x: INTEGER;

BEGIN
DeviceList[1] := GetDeviceList;
theDepthList[1] := DeviceList[1]^^.gdPMap^^.pixelSize;
FOR x := 2 TO 6 DO
BEGIN
DeviceList[x] := GetNextDevice(DeviceList[x - 1]);
IF DeviceList[x] <> NIL THEN
theDepthList[x] := DeviceList[x]^^.gdPMap^^.pixelSize
ELSE
x := 6;
END;
END;

If you need to find which device in the device list array created above is the
main device, use the "TestDeviceAttribute" function described on page 124. Here
is a code fragment showing how to use the function:

IF TestDeviceAttribute(DeviceList[1], mainScreen) THEN...

If the "TestDeviceAttribute" function returned "TRUE" or "1" in the example
above, then "DeviceList[1]" is the main screen. If the function returned
"FALSE" or "0", then the device is not the main screen. You can also use this
function to determine if the device is in color model. For example:

IF TestDeviceAttribute(DeviceList[1], gdDevType) THEN...

If the "TestDeviceAttribute" function in this example returned "TRUE" or "1",
then "DeviceList[1]" is in color mode; if it returned "FALSE" or "0", then it
is in monochrome mode.