Window Updates
Introduction to composition and
presentation of the window stack
Terminology
Term
Description
Surface
Contains one or more pixel buffers
Window
Element on screen which can be a portion
of a surface or a static color
Window Stack
List of windows and background color or
image
Display Layer
Hardware entity showing the surface of
the composited stack, e.g. an OSD plane
Swapping
One buffer is queued for display on the
layer, list of buffers is rotated by one
Windows
Property
Description
bounds
Rectangular output area, basis for
calculation of destination geometry,
borders, scaling…
source geometry
Portion of the window surface to be
shown on screen
destination geometry
Portion of the window bounds used to
show the window surface
bounds
destination geometry
Surface
source geometry
Stack
Composition
• The stack of windows is rendered onto a
surface for presentation on a display layer
• Updates are often clipped to an area
background
windows
update area
