• Antelope Release 5.9 Mac OS X 10.13.2 2019-05-01

 

NAME

BQLayer - BRTT Qt graphics extension for establishing a graphics backing store

SYNOPSIS


$(QTNATIVELIBS) -lbqplot_native -lbanner -lbrttutil -lbumapdata $(DBLIBS) $(TRLIBS)

#include "BQ.h"

DESCRIPTION

BQLayer objects provide graphics backing store buffers for other bqplot objects. Each BQLayer object is treated as a normal bqplot graphics item and must be associated with a BQViewport object. All of the other bqplot graphics items can be configured to render into a BQLayer object instead of directly into the graphics display. Each BQLayer object keeps its own QPixmap object that acts as the off-screen display buffer. Multiple bqplot graphics items can be associated with the same BQLayer object. The BQLayer backing pixmap is initialized with transparent pixels so that any kind of bqplot graphics item can be rendered into the buffer.

bqplot graphics items are associated with a BQLayer item with a call to the BQViewportItem setLayer function. Once a bqplot graphics item has been associated with a BQLayer object, then all rendering done by that item is done into the BQLayer off-screen pixmap resource. The drawing of the off-screen pixmap resource onto the graphics display is done when the BQLayer object is rendered according to its position in the BQViewport display list. The rendering of bqplot graphics items onto the BQLayer off-screen pixmap resources is only done when either the BQViewport window has changed size or scales or if the item's BQViewportItem setItemStale function, or the associated BQViewport setStale function has been called. In this way expensive rendering tasks, such as complex base maps, can be buffered so that they do not need to be re-rendered, as long as the base map itself or its size or scale do not change.

Generally BQLayer objects do not need to be created by the application programmer. Calls to BQViewportItem::setLayer will cause the automatic creation of the BQLayer object if it does not already exist. BQLayer objects are all given unique string names that are used to reference them. Multiple bqplot graphics item objects that are associated to the same named BQLayer object will all be rendered into the same BQLayer object in the order in which they were created. Note that the display list order is automatically adjusted so that the drawing of the BQLayer items associated with a group of other bqplot item objects will come after the rendering of those objects to the BQLayer object.

INHERITS FROM

BQViewportItem

CONSTRUCTOR

BQLayer(BQViewport *master, QString name);

Where "master" is the bqplot BQViewport item that acts as the master for the BQLayer item and name is the unique name of the BQLayer object. When the constructor is called directly and the named object already exists, then the old BQLayer object is deleted and a new one is made with the existing name.

METHODS

SEE ALSO

bqplot(3), BQViewport(3), BQViewportItem(3)

AUTHOR

Danny Harvey, BRTT
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