Minidriver-Supplied Halftone Patterns

When GDI-supported halftone methods are being used, GDI allows specification of customized halftone patterns. To specify customized halftone patterns, use option attributes for the halftone feature as follows:

  • The *rcHTPatternID, *HTPatternSize and *HTNumPatterns attributes allow you to describe halftone patterns that are stored in a resource DLL. Halftone pattern resources are three-dimensional arrays of binary data, starting on a DWORD address boundary. They can be specified using the following format, which calculates the correct size and provides the required address alignment:

    BYTE HTPatternResource [HTNumPatterns][(HTPatternSize.y*HTPatternSize.x+3) & ~3];

    Within an .rc file used to create a resource DLL, the pattern might be specified as follows:


    where halftone.bin is a file containing a halftone pattern.

  • The *HTCallbackID attribute allows you to indicate that you are implementing the IPrintOemUni::HalftonePattern method in a rendering plug-in. A unique *HTCallbackID value must be provided for each pattern the IPrintOemUni::HalftonePattern method supports.

You can provide halftone pattern resources, an IPrintOemUni::HalftonePattern method, or both, as follows:

  • If you provide only halftone patterns, Unidrv obtains the patterns from the resource DLL and passes them to GDI. The patterns cannot be encrypted.

  • If you provide only an IPrintOemUni::HalftonePattern method, the method must generate and return halftone patterns to Unidrv, which passes them to GDI.

  • If you want to place encrypted halftone patterns in a resource DLL, then you must also provide an IPrintOemUni::HalftonePattern method to decode the patterns and return them to Unidrv, which in turn passes them to GDI.

For more information about halftoning, see Customized Halftoning.