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This article mainly introduces Qt how to achieve string generation QR code function, the article introduces in great detail, has a certain reference value, interested friends must read it!

Preface

Recently, in sorting out the knowledge points encountered in the development project, I found a particularly interesting feature: using strings to generate QR code operations.

The following is the effect diagram of the implementation

Development environment

WIN10 environment + VS2017 + Qt 5.14.2 64-bit development environment

Implement step resource bundle data

To be honest, my development environment is really troublesome.

If you want to use Qt to use the QR code function, you must add the "qrencode" library. Compiled a dll library using cmake for the environment I am currently using

The compiled file contains two files: lib and src. If it is inconsistent with my development environment, it can be compiled by itself, and it is also very fast (I find that camke is really a good tool).

Configuration Properti

1: header file settin

2: static library settings

Description: set up according to the red area of the above three pictures.

You can find that I all have the same point when I set it up, and they all use relative paths.

Generally speaking, when many people do large-scale projects, they will use the relative path, even if each person puts the project on a different disk, there will be no data reading problem.

Speaking of which, then I will go on to say something beside the topic about configuration ~ I hope it will be helpful to you!

Digression: in that case, the exe we generated will also be placed in a separate directory, assuming we call it the bin file.

The exe generated by default in VS is generated into the corresponding folder depending on whether it is a debug or release environment. Currently, to merge the two environments, you need to modify the general operations in the configuration properties.

Finally, you also need to set the exe generation directory to the current path in the code, otherwise the corresponding file cannot be found when the relative path is used in the program!

QString qExePath = QCoreApplication::applicationDirPath (); QDir::setCurrent (qExePath)

These two sentences are best put into main.cpp to make the whole project effective.

QR code operation

Next comes our big story, how to use strings to generate QR codes.

1: create a QR operation class to draw QImage graphics

Define class: QORCodeOperation

# include # include class CQRCodeOperation {public: CQRCodeOperation (); ~ CQRCodeOperation (); QImage GeneratedGraphics (std::string sData, QSize nsize); / / generate graphics private: QPixmap mechimg Icon;}

Function (GeneratedGraphics)

Returns the QImage value of the graph by passing in the specified string and the width and height of the QR code.

In general, we will assign QIamge to the QLable to display.

Parameter (m_imgIcon)

QPximap type of member variables, mainly drawing graphics, at the beginning of the display effect students can see that the QR code added a picture, mainly used to display the picture.

2: generate QR code graphics QImage

2.1Definitions of QImage object store generated content

QImage image (nsize, QImage::Format_RGB32); image.fill (QColor ("# 000000"))

QImage stores an image based on the width and height of the set nsize size, and the program automatically aligns the data according to the image format, using a 32-bit RGB format (0xffrrggbb)

2.2: construct the drawing pointer

QPainter painter (& image); if (! painter.isActive ()) {return image;}

Construct the QPainter drawing pointer. Generally, when the incoming QSize data is 0, the subsequent operation cannot be performed, that is, isActiva = false.

2.3: get QRcode class instance based on string

QRcode * qrCode = QRcode_encodeString (sData.c_str (), 1, QR_ECLEVEL_L, QR_MODE_8, 1)

2.4: set dot brush and background brush

QColor colorForPoint ("# FFB6C1"); QColor colorForBackground ("# ffffff"); painter.setBrush (colorForBackground); painter.setPen (Qt::NoPen); painter.drawRect (0,0, image.width (), image.height ()); painter.setBrush (colorForPoint)

2.5: drawing Graph

Const double & & s = (qrCode- > width > 0)? (qrCode- > width): (1); const double & & aspect = image.width () / image.height (); const double & & scale = ((aspect > 1.0)? Image.height (): image.width () / sten for (int y = 0; y

< s; ++y){ const int &&yy = static_cast(y * s); for (int x = 0; x < s; ++x) { const int &&xx = yy + x; const unsigned char &b = qrCode->

Data [xx]; if (b & 0x01) {const double rx1 = x * scale, ry1 = y * scale; QRectF r (rx1, ry1, scale, scale); painter.drawRects (& r, 1);}

Here, in order to be lazy, the trinocular operator is used to judge the width value.

2.6: release the QRcode pointer

QRcode_free (qrCode)

2.7: add QR code graphics

In fact, the picture we show in the middle is relatively small, just overlay it directly on the QR code.

Painter.setRenderHint (QPainter::Antialiasing, true); / / Anti-aliasing int nLeft = (nsize.width ()-30) / 2witint nTop = (nsize.height ()-30) / 2nTop,30,30 rectPng (nLeft, nTop,30,30); painter.drawPixmap (rectPng, m_imgIcon)

2.8: end drawing

Painter.end ()

So far, the specific QR code drawing has been completed, we only need to return to the QImage where the drawing data is stored.

3: QR code function call

CQRCodeOperation dlg;QImage img = dlg.GeneratedGraphics (sText, QSize (250,250)); ui.labPng- > setPixmap (QPixmap::fromImage (img)). This is all the content of the article "how to generate a QR code by Qt". Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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