X11PCDisplayListObject.h

Classes

X11PCDisplayListObject -- Base class for caching of X11 device (ie. X11PixelCanvas) display lists. (full description)

class X11PCDisplayListObject

Interface

Public Members

virtual ~X11PCDisplayListObject()

virtual void translate(Int xt, Int yt) = 0

virtual void draw(::XDisplay *display, Drawable d, GC gc, Int xt, Int yt) = 0

virtual Char optType() const = 0

Protected Members

X11PCDisplayListObject()

X11PCDisplayListObject(const X11PCDisplayListObject &other)

X11PCDisplayListObject &operator=(const X11PCDisplayListObject &other)

Description

Review Status

Reviewed By:: Bob Garwood
Date Reviewed:: 2000/02/01

Prerequisite

X11PixelCanvas

Etymology

"X11PCDisplayListObject" is a contraction and concatenation of "X11PixelCanvas", "Display List" and "Object".

Synopsis

This class forms the base interface for a set of classes which provide storing (and optimisation) of drawing commands for the X11PixelCanvas class. Most primitive graphics routines available on the X11PixelCanvas, for example drawImage and drawRectangle, have corresponding objects derived from this class, which are constructed by the primitive routines, and then called upon to draw themselves when necessary.

Each instance of a class derived from X11PCDisplayListObject keeps with it information necessary to draw to the X11 drawable or to change the X11PixelCanvas's attributes. Furthermore, these objects tend to store the information necessary to do the drawing in native X11 format, or as close to that as is practicable, thus lending a level of optimisation to the drawing process.

Some X11PCDisplayListObjects take over the memory the PixelCanvas used to create the object when constructed and therefore undertake to destroy the memory when the X11PCDisplayListObject is destroyed. Examples of this include images and sets of points or lines.

Each derived class must implement the draw and translate functions correctly.

Motivation

Is is extremely convenient to place all output graphics commands (including context changes) in a display list for fast and efficient handling. The user gets control over drawn objects without knowing how the objects are drawn, or how they are cached.

Thrown Exceptions

None.

To Do

Nothing known.

Member Description

virtual ~X11PCDisplayListObject()

A virtual destructor is needed so that it will use the actual destructor in the derived class.

virtual void translate(Int xt, Int yt) = 0

Translate the object by the specified displacements.

virtual void draw(::XDisplay *display, Drawable d, GC gc, Int xt, Int yt) = 0

Draw to the current context provided with the translation given.

virtual Char optType() const = 0

Return a special character code identifying the type of drawing, and therefore enabling down-stream caching. Presently, the character codes are listed in X11PCCaceOpt.cc, and are used in calls to X11PixelCanvas::packDisplayList.