How to Maintain Aspect Ratio When Displaying Images in Qt\'s QLabel?

Preserving Aspect Ratio in Qt's QLabel with QPixmap

In Qt, displaying an image in a QLabel often poses the challenge of resizing while preserving its aspect ratio. This is especially important when dealing with dynamic changes in the source image's dimensions.

Keeping Aspect Ratio with Size Policy

To address this, adjust the label's QSizePolicy to allow for expansion or minimum expansion. For example:

<code class="cpp">QLabel label;
label.setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);</code>

Scaling the QPixmap

To scale the QPixmap within the QLabel while maintaining the aspect ratio, add the following code:

<code class="cpp">QPixmap pixmap; // Assumed loaded from a source
int labelWidth = label.width();
int labelHeight = label.height();
label.setPixmap(pixmap.scaled(labelWidth, labelHeight, Qt::KeepAspectRatio));</code>

Insert this code in two locations:

1. Whenever the pixmap is updated
2. In the resizeEvent of the widget containing the label

This setup ensures that the QLabel resizes to accommodate the QPixmap while preserving its aspect ratio, following the available space.

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