C++ Qt绘制一个带边框的填充圆角矩形
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Qt drawing a filled rounded rectangle with border
提问by SexyBeast
I want to draw a rectangle with rounded corners (border radius same for all 4 corners) with a specific color filling the entire rectangle, and a separate border color (say border is 1 px wide).
我想绘制一个带圆角的矩形（所有 4 个角的边框半径相同），用特定颜色填充整个矩形，并使用单独的边框颜色（比如边框宽 1 像素）。
From my observation, Qt provides three methods - fillRectand drawRectand drawRoundedRect. I have tried them, they don't work like I want to. There is no method like fillRoundedRect. Which means that I can draw a rounded rectangle but it won't be filled with the color I want.
根据我的观察，Qt 提供了三种方法 - fillRectanddrawRect和drawRoundedRect。我已经试过了，它们不像我想要的那样工作。没有像fillRoundedRect. 这意味着我可以绘制一个圆角矩形，但它不会填充我想要的颜色。
How do I do it? And also, I read that due to some aliasing problems, the corners are often rendered as unequal. How do I set it as equal for all four? Will painter.setRenderHint(QPainter::Antialiasing)suffice? Or do I have to do anything else?
我该怎么做？而且，我读到由于一些锯齿问题，角落经常呈现不等。我如何将它设置为所有四个相等？将painter.setRenderHint(QPainter::Antialiasing)足够？还是我必须做其他事情？
回答by dtech
You can create a QPainterPath, add the rounded rect to it, and then fill and stroke it:
您可以创建一个QPainterPath，向其添加圆角矩形，然后填充和描边它：
QPainter p(this);
p.setRenderHint(QPainter::Antialiasing);
QPainterPath path;
path.addRoundedRect(QRectF(10, 10, 100, 50), 10, 10);
QPen pen(Qt::black, 10);
p.setPen(pen);
p.fillPath(path, Qt::red);
p.drawPath(path);
Note that even with antialiasing, 1 px border will probably never really look good, especially on a low DPI desktop monitor, on a high DPI mobile device it will be almost invisible.
请注意，即使使用抗锯齿，1 像素边框也可能永远不会真正好看，尤其是在低 DPI 桌面显示器上，在高 DPI 移动设备上它几乎不可见。
If you create the rectangle as QRectF(9.5, 9.5, 100, 50)it will look better with 1 px antialiased border, because it will "snap" on the right pixel:
如果您创建矩形，因为QRectF(9.5, 9.5, 100, 50)它会使用 1 px 抗锯齿边框看起来更好，因为它会“捕捉”在正确的像素上：
