Question

在Qt中，我有一个宽度为5像素，高度为4像素的Qpixmap，我用宽度为.08和高度为.08的矩形填充它，但形成的矩形与我给出的尺寸不同。我想画出等长的黑色和白色矩形

QLabel *a=new QLabel();
QPixmap b(5,4);
a->setFixedSize(b.size());
QPainter painter(&b);
heightOfCheckeredBox=.08;
widthOfCheckeredBox=.08;
bool switchBetweenBlackAndWhiteBoxRowDirection=true;
int  switchBetweenBlackAndWhiteBoxColumnDirection=0;
for(qreal i=0;i<4;i+=heightOfCheckeredBox)
{
    for(qreal j=0;j<5;j+=widthOfCheckeredBox)
    {
        if(switchBetweenBlackAndWhiteBoxRowDirection)
        {



            painter.setPen(Qt::white);
            painter.setBrush(Qt::white);

            switchBetweenBlackAndWhiteBoxRowDirection=false;

        }
        else
        {

            painter.setPen(Qt::gray);
            painter.setBrush(Qt::gray);
            switchBetweenBlackAndWhiteBoxRowDirection=true;
        }

        QRectF rectangle(j,i,widthOfCheckeredBox,heightOfCheckeredBox);
        painter.drawRect(rectangle);

    }

    switchBetweenBlackAndWhiteBoxColumnDirection++;
    if(int(switchBetweenBlackAndWhiteBoxColumnDirection)%2==0)
        switchBetweenBlackAndWhiteBoxRowDirection=true;
    else
        switchBetweenBlackAndWhiteBoxRowDirection=false;
}

a->setPixmap(b);
a->show();

Answer 1

由于您在没有抗锯齿的情况下进行绘制，因此微小的像素大小毫无意义 - 您的期望是什么？

像素图的大小以像素为单位。您的像素图包含5x4 = 20像素。你试图在它上画20个矩形。为此，每个矩形必须是正好一个像素宽和高的正方形。唉，你试图绘制比像素小12.5倍的正方形。这没有多大意义，我不知道你从哪里得到0.08的价值。只需绘制一个像素宽的正方形。

示例：

// https://github.com/KubaO/stackoverflown/tree/master/questions/checkered-paint-42205180
#include <QtWidgets>

QPixmap checkers(const QSizeF & rectSize, const QSize & pixmapSize) {
   QPixmap pixmap{pixmapSize};
   QPainter painter{&pixmap};
   painter.setPen(Qt::NoPen);
   const QColor colors[] = {Qt::white, Qt::black};
   QPointF pos{};
   bool oddRow{}, color{};
   while (pos.y() < pixmap.height()) {
      painter.setBrush(colors[color ? 1 : 0]);
      painter.drawRect({pos, rectSize});
      color = !color;
      pos.setX(pos.x() + rectSize.width());
      if (pos.x() >= pixmap.width()) {
         pos.setX({});
         pos.setY(pos.y() + rectSize.height());
         oddRow = !oddRow;
         color = oddRow;
      }
   }
   return pixmap;
}

int main(int argc, char ** argv) {
   QApplication app{argc, argv};
   QLabel label;
   auto pix = checkers({1, 1}, {60, 30});
   label.resize(200, 200);
   label.setAlignment(Qt::AlignCenter);
   label.setPixmap(pix);
   label.show();
   return app.exec();
}

Qpainter的drawRect函数没有给出相等维度的矩形

1 个答案: