Limitations There are some known limitations with the added CopyBits() support that you should be aware of. They are: - Extremely complex clipping regions may occasionally fail on Level 1 or Level 2 devices in low printer memory conditions. The result is that the output will not preserve the clip, and the image will print as if the
maskRgn parameter is ignored. Specifically, for PostScript Level 1 printers, there is a hard coded limit to how complex a clip can be, regardless of the printer's installed memory. If the clip is more complex than this limit, the LaserWriter driver ignores the maskRgn parameter. For Level 2 printers, the limits are completely memory-based and generally much more flexible. However, once again, in low-memory conditions, the clip may still fail. On PostScript Level 3 printers, all clips should always print correctly regardless of the complexity of the clip since the driver uses the PostScript Level 3 masked image to support this feature.
- Since the LaserWriter driver implements the transparent mode via clipping, complex transparent regions may occasionally fail on Level 1 or Level 2 devices in low-memory conditions as described above. The result is that the output does not preserve the transparency, and the pixels image with the background color instead.
- For 2, 4, and 8-bit images with a color look-up table (CLUT), the LaserWriter 8.5.1 driver only supports one index which maps to the background color. Although the CLUT may contain many index values which have the background color and are therefore, in principle, transparent when displayed onscreen, the driver searches the look-up table for the first index which corresponds to the background color. Index samples with that index value are printed as transparent. Other index values which correspond to the background color are not treated as transparent but are printed as the background color.
- In order to maintain compatibility with many applications, the LaserWriter 8.5.1 driver will ignore a
maskRgn which is an empty region under some circumstances (e.g. some rotated text and graphics). Some applications have used the fact that previous drivers always ignored the maskRgn parameter to clip out certain data when printing to QuickDraw printers. Relying on this 'feature' is not recommended, and the fact that there are some edge cases where a zero clip is ignored for compatibility reasons may be a temporary 'feature' of the driver. To avoid accidentally encountering these cases, when you really want a zero clip, either do not draw the image (preferred) or use grafPort clipping to clip it. |