Qt Learning notes
Table of Contents
Draw Images in Qt
paint system
https://qt-project.org/doc/qt-4.7/paintsystem.html#id-dfb6c752-0d75-4b13-8270-659d558a3ae7
QPainter is used to perform drawing operations, QPaintDevice is an abstraction of a two-dimensional space that can be painted on using a QPainter, and QPaintEngine provides the interface that the painter uses to draw onto different types of devices. The QPaintEngine class is used internally by QPainter and QPaintDevice, and is hidden from application programmers unless they create their own device type.
QPainter
QPainter provides highly optimized functions to do most of the drawing GUI programs require. It can draw everything from simple lines to complex shapes like pies and chords. It can also draw aligned text and pixmaps. Normally, it draws in a "natural" coordinate system, but it can also do view and world transformation. QPainter can operate on any object that inherits the QPaintDevice class.
The common use of QPainter is inside a widget's paint event: Construct and customize (e.g. set the pen or the brush) the painter. Then draw. Remember to destroy the QPainter object after drawing. For example:
void SimpleExampleWidget::paintEvent(QPaintEvent *)
{
QPainter painter(this);
painter.setPen(Qt::blue);
painter.setFont(QFont("Arial", 30));
painter.drawText(rect(), Qt::AlignCenter, "Qt");
}
The core functionality of QPainter is drawing, but the class also provide several functions that allows you to customize QPainter's settings and its rendering quality, and others that enable clipping. In addition you can control how different shapes are merged together by specifying the painter's composition mode.
Coordinate System
https://qt-project.org/doc/qt-4.7/coordsys.html#id-453ffa45-ef2c-4360-8538-c4aa5e3790fe
The QPaintDevice class is the base class of objects that can be painted: Its drawing capabilities are inherited by the QWidget, QPixmap, QPicture, QImage, and QPrinter classes. The default coordinate system of a paint device has its origin at the top-left corner. The x values increase to the right and the y values increase downwards. The default unit is one pixel on pixel-based devices and one point (1/72 of an inch) on printers.
Anti-aliased Painting
QPainter painter(this);
painter.setRenderHint(
QPainter::Antialiasing);
painter.setPen(Qt::darkGreen);
painter.drawRect(1, 2, 6, 4);
Note
Qt is an open-source project, the source code is available at http://qt.gitorious.org/.
Post by: Jalen Wang (转载请注明出处)