Color mixing

GDDM V3R2 Base Application Programming Guide

Color mixing

GDDM V3R2 Base Application Programming Guide
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With two exceptions, overlying primitives are plotted on top of underlying ones. The resulting colors depend on the physical and chemical interactions of the inks.

The exceptions apply in underpaint or overpaint mode only. They are:

Any primitive, other than an image or image symbol, that underlies a solid shaded area is clipped at the edge of the area.
If the overlying primitive is:
- In background color or explicit white (colors 8 and minus.2),
- And is a line (or arc), a vector symbol (or marker), or a solid-shaded area,
then any underlying primitives, other than images and image symbols, are clipped to allow background to show through, as explained in the section "Colors" in topic 21.3.5.1.

A plotted picture showing the 8 GDDM line types supported on plotters in single and double line width.

Figure 118. The eight GDDM line types for plotters

In summary, underlying primitives other than images and image symbols are clipped at the boundaries of all overlying solid-shaded areas. They are also clipped at overlying background-color vectors.

There is no such clipping in mix mode.

If you use underpaint mode for a picture that is displayed on the screen of a 3270-PC/G or /GX workstation that is also being plotted, the results differ. Underpaint mode is not supported on these displays; it is implemented as overpaint.

Performance considerations: Reverse clipping to give white graphics can use a lot of processing time in the host computer, depending on the complexity of the picture. In order to minimize the processing you are recommended to:

Keep the number of lines and characters in colors -2 and 7 to a minimum.
Avoid drawing lines, characters, or solid-shaded areas (especially complex ones) in colors -2 and 7, on top of solid shaded areas.

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