Technical Q&As

QTICM 03 - GDHasScale (1-May-95)

GDHasScale returns the closest possible scaling that a particular screen device can be set to in a given pixel depth. It returns scaling information for a particular GDevice for a requested depth. It allows you to query a GDevice without actually changing it. For example, if you specify 0x20000, but the GDevice does not support it, GDHasScale will return with noErr, and a scale of 0x10000. Remember, it checks for a supported depth, so your requested depth must be supported by the GDevice. GDHasScale references the video driver through the graphics device structure.

For multiple screens, see "Multiple Screens Revealed" in develop #10 to find out how to walk the GDeviceList.

pascal OSErr GDHasScale(GDHandle gdh,short depth,Fixed *scale)

gdh A handle to a screen graphics device.

depth Pixel depth of screen device. Use this field to specify which pixel depth scaling information should be returned for.

scale A pointer to a fixed point scale value. On input, this field should be set to the desired scale value. On output, this field will contain the closest scale available for the given depth. A scale of 0x10000 indicates normal size, 0x20000 indicates double size, and so on.

Errors:

cDepthErr The requested depth is not supported.

cDevErr Not a screen device.

controlErr Video driver can not respond to this call.