little tips of painter.drawRect in Qt

Posted 2020-08-11

一个QImage或QPixmap新建变量时，第一次填充图片时设置的宽高正常（fill），其后的绘制操作（draw）则会在绘制的矩形底边和右边加上painter.pen().width()

在下面代码17行设置端点查看内存可以直观看到只在右边和底边++

 1 // 1.  生成掩码图
 2     const int width = 32;
 3     const int height = 20;
 4     QImage maskImg(width, height, QImage::Format_Mono);
 5     QPainter maskPainter(&maskImg);
 6     //
 7     maskPainter.setPen(QPen(Qt::white, 0));
 8     maskPainter.setBrush(Qt::white);
 9     maskPainter.drawRect(0, 0, width, height);
10     maskPainter.setPen(QPen(Qt::black, 0));
11     maskPainter.setBrush(Qt::black);
12     maskPainter.drawRect(16, -16, width, height);
13     maskPainter.setPen(QPen(Qt::black, 0));
14     maskPainter.setBrush(Qt::black);
15     maskPainter.drawRect(16, 16, 2, 3);
16 
17     maskImg.save("/home/lt47/Desktop/ORIGIN.jpg");
18     qDebug() << maskImg.byteCount();
19     qDebug() << maskImg.bytesPerLine();
20     QRgb b = maskImg.pixel(16,20);
21     qDebug() << qRed(b) << qGreen(b) << qBlue(b);
22     QRgb ww = maskImg.pixel(15,20);
23     qDebug() << qRed(ww) << qGreen(ww) << qBlue(ww);