The color attribute defines the color used to draw a primitive or an object. The mix attribute determines how the color of a primitive or an object is combined with the color of the drawing surface, or any other objects on the surface.
The marker color defines the color used to draw the output from any of the IBM OS/2 marker functions. When a presentation space is created, the marker color initial default is black. Markers are one of the primitives that have a foreground and background color, as shown in the following figure.
For image markers, the colors are determined by the setting of pels. For
vector markers, the foreground consists of the arcs and lines that define
the marker. The background color appears between the foreground lines. The
marker can be solid, or filled, in which case the background color does
not appear between the foreground lines.
Marker Primitives
Marker primitives have both a color and background color attribute. The mix attribute controls the combination of marker color with drawing-surface color, while the background mix attribute controls the combination of the marker box color with the drawing-surface color.
When a presentation space is created, the marker mix attribute initial default is FM_OVERPAINT. The overpaint mix attribute specifies that the marker color is not to be modified by the color of the drawing surface. If the marker mix attribute is changed, the marker color is mixed with colors that are already on the drawing surface.
The marker background color initial default is CLR_BACKGROUND. Usually this is defined by the application to the same color as the drawing surface. The marker background mix attribute initial default is BM_LEAVEALONE. The leave-alone mix background attribute specifies that the marker background color is not drawn. The box that effectively surrounds the marker appears only if the marker background mix attribute is changed.
To specify a new color or mix attribute call GpiSetAttrs. This function accepts as input the type of primitive, for example PRIM_MARKER, a list of attributes that are to be changed, a list of attributes that are to be set to their default values, and the values for the attributes that are to be changed. GpiSetAttrs is useful to specify colors and mix attributes just for a specific data structure- MARKERBUNDLE, for example. GpiSetAttrs also provides some protection against invalid colors.
To determine the current marker color and mix attribute call GpiQueryAttrs. This function accepts as input the primitive type and the attributes in question. It returns as output an array of values for the specifically queried attributes.
To reset the default marker color and mix attribute, just as with any other attribute specified in the MARKERBUNDLE data structure, call GpiSetDefAttrs. This function accepts as input the type of primitive, for example PRIM_MARKER, the attributes to be changed, and the values that will become the new default values. The changing of default values is important when working with segments. Changing the default values during a series of drawing functions is not recommended.
The marker color and mix attribute also can be specified with:
However, these functions have the disadvantage of specifying the foreground and background color or mix attribute for all primitive BUNDLE data structures that have the respective component.
There are four query functions that determine the color and mix attribute as specified by GpiSet... functions:
If the marker color, marker background color, mix attribute, or background mix attribute were specified individually, the queries can return a value inconsistent with the current marker attribute.