Operation Manual

Fill, Lines, Colours, and Transparency 169
Composite opacity
An individual object can take a specific opacity setting. However, when multiple
objects are grouped (see p. 135), the group can be given a composite opacity,
affecting all group objects to the same extent. Composite opacity is possible by
using the Opacity slider on the Colour tab.
Drawing without
opacity
Result of objects
selected individually,
and assigned 50%
opacity.
Result of objects
grouped, with 50%
composite opacity
applied to group.
Any opacity on objects prior to grouping will be honoured;
composite opacity, when applied, will further increase the
transparency of that object.
If you ungroup, the opacity of the object before grouping is
reverted to.
Knockout groups
When working with grouped semi-transparent objects you can use knockout
groups to control how an object's colour and opacity interacts with an
overlapping object's colour/opacity in the same group. When disabled (default),
the "combined" colour/opacity is a blend of both objects. When enabled, the
lower colours/opacity are "knocked out", i.e., replaced by the upper
colours/opacity, avoiding potentially unwanted overlapping colour
combinations.
For more information about grouping, see Grouping objects on p. 135.