Exceptional Cases When Working With Color Devices

If your application always specifies colors in RGBColor records, Color QuickDraw automatically handles the colors on both indexed and direct devices. However, if your application does not specify colors in RGBColor records, your application may need to create and use special-purpose CGrafPort , PixMap , and GDevice records with the routines described in the chapter "Offscreen Graphics Worlds."

If your application must work with CGrafPort , PixMap , and GDevice records in ways beyond the scope of the routines described elsewhere in this book, the following guidelines may aid you in adapting Color QuickDraw to color graphics devices.

Don't draw directly to the screen. Create your own offscreen graphics world (as described in the chapter "Offscreen Graphics Worlds") and use the CopyBits , CopyMask , or CopyDeepMask routine (described in the chapter "Color QuickDraw") to transfer the image to the screen.
Don't directly change the fgColor or bkColor fields of a GrafPort record and expect them to be used as the pixel values. Color QuickDraw recalculates these values for each graphics device. If you want to draw with a color with a particular index value, use a palette with explicit colors, as described in Inside Macintosh: Advanced Color Imaging . For device-independent colors, use the RGBForeColor and RGBBackColor procedures, described in the chapter "Color QuickDraw" in this book.
Don't copy a GDevice record's PixMap record. Instead, use the NewPixMap function or the CopyPixMap procedure, and fill all the fields. (These routines are described in the chapter "Color QuickDraw.") The NewPixMap function returns a PixMap record that is cloned from the PixMap record pointed to by the global variable TheGDevice . If you don't want a copy of the main screen's PixMap record--for example, you want one that is a different pixel depth--then you must fill out more fields than just pixelSize : you must fill out the pixelType , cmpCount , and cmpSize fields. Set the pmVersion field to 0 when initializing your own PixMap record. For future compatibility you should also set the packType , packSize , planeBytes , and pmReserved fields to 0. Don't assume a PixMap record has a color table--a pixel map for a direct device doesn't need one. For compatibility, a PixMap record for a direct device should have a dummy handle in the pmTable field that points to a ColorTable record with a seed value equal to cmpSize ¥ cmpCount and a ctSize field set to 0.
Fill out all the fields of a new GDevice record. When creating an offscreen GDevice record by calling NewGDevice with the mode parameter set to -1, you must fill out the fields of the GDevice record (for instance, the gdType field) yourself. If you want a copy of an existing GDevice record, copy the gdType field from it. If you explicitly want an indexed device, assign the clutType constant to the gdType field.

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