qcam: Support scaling of the viewfinder

The viewfinder is drawn using a QLabel. This could support scaling
through QLabel::setScaledContents(), but in a very inefficient way. To
maintain reasonable efficiency, turn the viewfinder into a QWidget and
draw the image directly using a QPainter.

No performance change was noticed running on a fast x86 machine, and
performance was 60% higher when scaling up to full screen compared to
QLabel.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/qcam/viewfinder.h b/src/qcam/viewfinder.h
index 33bdb146..ef5fd45b 100644
--- a/src/qcam/viewfinder.h
+++ b/src/qcam/viewfinder.h
@@ -7,13 +7,13 @@
 #ifndef __QCAM_VIEWFINDER_H__
 #define __QCAM_VIEWFINDER_H__
 
-#include <QLabel>
+#include <QWidget>
 
 #include "format_converter.h"
 
 class QImage;
 
-class ViewFinder : public QLabel
+class ViewFinder : public QWidget
 {
 public:
 	ViewFinder(QWidget *parent);
@@ -23,6 +23,10 @@ public:
 		      unsigned int height);
 	void display(const unsigned char *rgb, size_t size);
 
+protected:
+	void paintEvent(QPaintEvent *) override;
+	QSize sizeHint() const override;
+
 private:
 	unsigned int format_;
 	unsigned int width_;