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. Both attributes also are described in Color and Mix Attributes.
The area color defines the color used to fill the output from any of the IBM OS/2 area functions, when necessary. The area primitive is the only primitive in which the color can be changed during the drawing of the area. Therefore, this attribute, more than the other area attributes, depends on the current value as described in Attribute Currentness.
When a presentation space is created, the area color initial default is black. The pattern symbol initial default, explained previously, is solid. Areas are one of the primitives that have a foreground and background color, as shown in the following figure. The appearance of the area also depends on the pattern symbol.
Area Primitives
Area primitives have both a color and background color attribute. The background color does not appear if the pattern symbol is solid, and the background color is undefined if the pattern symbol is a customized, multi-colored bit map.
When a presentation space is created, the area mix attribute initial default is FM_OVERPAINT. The overpaint mix attribute specifies that the area color is not to be modified by the color of the drawing surface. If the area mix attribute is changed, the area color is mixed with colors that are already on the drawing surface.
When the pattern symbol is solid, the color that fills the area, if necessary, is the current area foreground color. If the pattern symbol is changed to be a pattern of vertical lines, for example, the color of those lines is the current area foreground color. Inside of the area bracket, there can be other colors if these colors are the current color for primitives such as lines or arcs, that are drawn within the area bracket. These colors are not specifically defined or influenced by the area foreground color.
The area background color initial default is CLR_BACKGROUND. Usually this is defined by the application to the same color as the drawing surface. If the pattern symbol is solid, the area background color does not appear. If the pattern symbol is changed to be a pattern of vertical lines, for example, the color in between those lines is the current area background color.
The area background mix attribute initial default is BM_LEAVEALONE. The leave-alone background mix attribute specifies that the area background color is not drawn. This means that for a nonsolid pattern symbol, the drawing-surface color or the color of an object, not created by the area bracket, but on the drawing surface, shows through the nonsolid pattern. The area background color, for nonsolid pattern symbols, appears only if the background mix attribute is changed to overpaint, BM_OVERPAINT.
If you have customized the pattern symbol with a bit map, the color definitions of the area primitive change. The foreground color corresponds to the color of the pels that are specified ON in the fill-pattern bit map. The background color corresponds to the color of the pels that are specified OFF in the fill-pattern bit map. The foreground and background mix attribute do not change.
Note: Background color and mix attribute only apply to monochrome (2-color) fill patterns. The bit set to 0 is defined as the background and the bit set to 1 is defined as the foreground.
A multi-colored bit map is unaffected by the background color and mix attributes.
To specify a new color or mix attribute call GpiSetAttrs. This function accepts as input the type of primitive, for example PRIM_AREA, 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 -for example the AREABUNDLE structure. GpiSetAttrs also provides some protection against invalid colors.
To determine the current area 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 area color and mix attribute, just as with any other attribute specified in the AREABUNDLE. data structure, call GpiSetDefAttrs. This function accepts as input the type of primitive, for example PRIM_AREA, 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 area 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 queries that determine the color and mix attribute as specified by GpiSet... functions:
If the area color, area background color, mix attribute, or background mix attribute were specified individually, the aforementioned queries can return a value inconsistent with the current area attribute.