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A mirror of a sheet which is not shared with any of the ancestors of the sheet. All grafted McCLIM sheets have mirrors, but not all have direct mirrors. A McCLIM sheet that does not have a direct mirror uses the direct mirror of its first ancestor having a direct mirror for graphics output. Asking for the direct mirror of a sheet that does not have a direct mirror returns nil.
Whether a McCLIM sheet has a direct mirror or not, is decided by the frame manager. Some frame managers may only allow for the graft to be a mirrored sheet. Even frame managers that allow hierarchical mirrors may decide not to allocate a direct mirror for a particular sheet. Although sheets with a direct mirror must be instances of the class mirrored-sheet-mixin, whether a McCLIM sheet has a direct mirror or not is not determined statically by the class of a sheet, but dynamically by the frame manager.
A device window such as an X11 window that parallels a sheet in the CLIM sheet hierarchy. A sheet having such a direct mirror is called a mirrored sheet. When drawing functions are called on a mirrored sheet, they are forwarded to the host windowing system as drawing commands on the mirror.
CLIM sheets that are not mirrored must be descendents (direct or indirect) of a mirrored sheet, which will then be the sheet that receives the drawing commands.
A sheet in the CLIM sheet hiearchy that has a direct
parallel (called the direct mirror) in the host windowing
system. A mirrored sheet is always an instance of the class
mirrored-sheet-mixin, but instances of that class are not
necessarily mirrored sheets. The sheet is called a mirrored sheet only
if it currently has a direct mirror. There may be several reasons for
an instance of that class not to currently have a direct mirror. One is
that the sheet is not grafted. Only grafted sheets can have
mirrors. Another one is that the frame manager responsible for
the look and feel of the sheet hierarchy may decide that it is
inappropriate for the sheet to have a direct mirror, for instance if the
underlying windowing system does not allow nested windows inside an
application, or that it would simply be a better use of resources not to
create a direct mirror for the sheet. An example of the last example
would be a stream pane inside a the viewport of a
scroller pane. The graphics objects (usually text) that appear
in a stream pane can have very large coordinate values, simply because
there are many lines of text. Should the stream pane be mirrored, the
coordinate values used on the mirror may easily go beyond what the
underlying windowing system accepts. X11, for instance, can not handle
coordinates greater than 64k (16 bit unsigned integer). By not having a
direct mirror for the stream pane, the coordinates will be translated to
those of the (not necessarily direct) mirror of the viewport
before being submitted to the windowing system, which gives more
reasonable coordinate values.
It is important to realize the implications of this terminology. A
mirrored sheet is therefore not a sheet that has a mirror. All grafted
sheets have mirrors. For the sheet to be a mirrored sheet it has to
have a direct mirror. Also, a call to sheet-mirror
returns a mirror for all grafted sheets, whether the sheet is a mirrored
sheet or not. A call to sheet-direct-mirror, on the other
hand, returns nil if the sheet is not a mirrored sheet.
The transformation that transforms coordinates in the coordinate system of a mirror (i.e. the native coordinates of the mirror) to native coordinates of its parent in the underlying windowing system. On most systems, including X, this transformation will be a simple translation.
Each mirror has a coordinate system called the native coordinate system. Usually, the native coordinate system of a mirror has its origin in the upper-left corner of the mirror, the x-axis grows to the right and the y-axis downwards. The unit is usually pixels, but the frame manager can impose a native coordinate system with other units, such as millimeters.
The native coordinate system of a sheet is the native coordinate system of its mirror (direct or not). Thus, a sheet without a direct mirror has the same native coordinate system as its parent. To obtain native coordinates of the parent of a mirror, use the mirror transformation.
The native region of a sheet is the intersection of its region and the sheet region of all of its parents, expressed in the native coordinates of the sheet.
A bounded area of an otherwise infinte drawing plane that is visible unless it is covered by other visible areas.
The coordinate system of coordinates obtained by application of the user transformation.
The region of a sheet determines the visible part of the drawing plane. The dimensions of the sheet region are given in sheet coordinates. The location of the visible part of a sheet within its parent sheet is determined by a combination of the sheet transformation and the position of the sheet region.
For instance, assuming that the sheet region is a rectangle with its upper-left corner at (2, 1) and that the sheet transformation is a simple translation (3, 2). Then the origin of the sheet coordinate system is at the point (3, 2) within the sheet coordinate system of its parent sheet. The origin of its the coordinate system is not visible, however, because the visible region has its upper-left corner at (2, 1) in the sheet coordinate system. Thus, the visible part will be a rectangle whose upper-left corner is at (5, 3) in the sheet coordinate system of the parent sheet.
Panes and gadgets alter the region and sheet transformation of the underlying sheets (panes and gadgets are special kinds of sheets) to obtain effects such as scrolling, zooming, coordinate system transformations, etc.
The transformation used to transform sheet coordinates of a sheet to sheet coordinates of its parent sheet. The sheet transformation determine the position, shape, etc. of a sheet within the coordinate system of its parent.
Panes and gadgets alter the transformation and sheet region of the underlying sheets (panes and gadgets are special kinds of sheets) to obtain effects such as scrolling, zooming, coordinate system transformations, etc.
A clipping region used to limit the effect of drawing functions. The user clipping region is stored in the medium. It can be altered either by updating the medium, or by passing a value for the :clipping-region drawing option to a drawing function.
The coordinate system of coordinates passed to the drawing functions.
A transformation used to transform user coordinates into sheet coordinates. The user transformation is stored in the medium. It can be altered either by updating the medium, or by passing a value for the :transformation drawing option to a drawing function.