Qt Common Class (7)--qpixmap

Source: Internet
Author: User
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The Qpixmap class represents the image, which is implemented in the Qtgui shared library.

Structure

The Qpixmap object generated by the following constructor is an empty image:

Qpixmap ();     Constructs an empty image with a size of 0

The following constructor generates the size of the Qpixmap object, but the image data is not initialized:

Qpixmap (const qsize &size);     Constructs an image of size, the image data is uninitialized
qpixmap (int width, int height);    Equivalent to Qpixmap (qsize (width, height));

The following constructor can load an image from a specified file and generate a Qpixmap object:

Qpixmap (const QString &filename, const char *format = 0, Qt::imageconversionflags flags = Qt::autocolor);

The meanings of each of its parameters are explained below.

1) FileName: file name.

2) Format: A string that represents an image file and, if 0, is automatically recognized.

3) Flags: Represents the color conversion mode.


If the image file fails to load, an empty image is generated, where the flags parameter has the following values.

1) Qt::autocolor: Automatically determined by the system.

2) Qt::coloronly: color mode.

3) Qt::monoonly: Monochrome mode.


Image parameters

The following member functions can obtain information about the image represented by the Qpixmap object:

int depth () const;     Color depth, both the number of bits per pixel of the
int width () const;     Image width, in pixels of
int height () const;   Image height, Unit is pixel
qsize size () cosnt;  The size of the image, i.e. qsize (width (), height ());
Qrect rect () const;   The rectangular area of the image, i.e. Qrect (Qpoint (0,0), size ());


Loading and saving images

Use the following member function to load an image from a file:

BOOL Load (const QString &filename, const char *fornat = 0, Qt::imagecoversionflags flags = Qt::autocolor);


Here the meaning of each parameter is the same as in the constructor, and a return value of TRUE indicates that the load was successful and false indicates that the load failed. The opposite action is to save the image represented by Qpixmap to a file, using the following member functions:

BOOL Save (const QString &filename, const char *format = 0, int quality =-1) const;

The meanings of each parameter and the return value are explained below.

1) FileName: file name.

2) Format: String that represents the format of the image file, and if 0, the file format is automatically determined based on the suffix of the file name.

3) Quality: For lossy compressed file format, it represents the quality of image preservation, the lower the quality, the greater the compression rate. A value range of 0~100,-1 indicates the default value is taken.

4) Return value: True indicates that the save was successful and false indicates that the save failed.


Judge

The following member function can determine whether an Qpixmap object is an empty image:

BOOL IsNull () const;     Determine if the image is empty


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