haiku/docs/user/interface/_interface_intro.dox

/*
 * Copyright 2010 Haiku, Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 *
 * Authors:
 *		Alex Wilson, yourpalal2@gmail.com
 */


/*!
	\page interface_intro Introduction to the Interface Kit
	\ingroup interface

	\section Overview

	The Interface Kit holds all the classes you'll need to develop a GUI.
	Building on the messaging facilities provided by the Application Kit,
	the Interface Kit can be used to create a responsive and attractive
	graphical user interface.

	The most important class in the Interface Kit is the BView class, which
	handles drawing and user interaction. Pointer and keyboard events are
	processed in this class. 

	Another important class is the BWindow class, which holds BViews and makes
	them visible to the user. The BWindow class also handles BView focusing
	and BMessage dispatching, among other things.

	A new addition Haiku has added over the BeOS API is the Layout API, which
	is based around the BLayoutItem and BLayout classes. These classes will
	take care of making sure all your GUI widgets end up where you want them,
	with enough space to be useful. You can start learning the Layout API 
	by reading the \ref layout_intro.

	\section coordinatespaces Coordinate spaces

	All APIs using coordinates (such as BRect or BPoint) refer to
	a specific space where these coordinates are interpreted. BView and
	BWindow provide various conversion function to translate coordinates
	between different spaces, as needed, or provide separate methods such as
	BView Bounds() and Frame(), returning results in different spaces as needed.

	The initial coordinate space, from which all others are derived,  is the
	screen space. Its origin is at the center of the screen's top-left pixel.
	Coordinates can be converted between this and a specific window or view
	space is done using the ConvertToScreen and ConvertFromScreen methods of
	the corresponding object.

	Each BWindow has its own coordinate space. Its origin is at the center of
	the top-left pixel of the window client area (just inside the window border).
	Root level views added to the window have their frame rectangle defined in
	this space.

	Each BView also gets its own coordinate space. The origin is initially at the
	top left of the view, but this can be changed by scrolling the view
	(programatically using ScrollBy or ScrollTo, or by the user acting on a scrollbar).

	Additionally, each BView also has a drawing space. This is further transformed
	from the BView coordinate space by calls to SetOrigin, SetScale, SetTransform,
	ScaleBy, RotateBy, and TranslateBy. The effects of the first two of these
	methods are independant from the other four, and it's not recommended to mix
	the two types of transformations in the same BView. Note that this is the only space
	that can be scaled and rotated, and translated by non-integer units. All other
	coordinate spaces are only translations of the screen one and remain aligned on pixels.

	All drawing operations in a BView use coordinates specified in the drawing space.
	However, the update rect passed to the Draw method (or passed to the Invalidate
	method) is in the BView base coordinate space. Conversion between the two can
	be done using the affine transform returned by BView::Transform, or in case the
	legacy transformation functions are used, by applying the scale and origin returned
	by the Scale() and Origin() functions.
*/