How to create circle icon from image file? - c++

Question

In my customized QWidget paintEvent method, I want to draw a circle with a circle shaped image icon. The source image is loaded from file and then automatically casted into circle using QPainter composition. How to do it? Thank you!
void DotGraphView::paintNodes(QPainter & painter)
{
painter.setPen(Qt::blue);
painter.drawEllipse(x, y, 36, 36);
QPixmap icon("./image.png");
QImage fixedImage(64, 64, QImage::Format_ARGB32_Premultiplied);
QPainter imgPainter(&fixedImage);
imgPainter.setCompositionMode(QPainter::CompositionMode_SourceIn);
imgPainter.drawPixmap(0, 0, 64, 64, icon);
imgPainter.setCompositionMode(QPainter::CompositionMode_SourceIn);
imgPainter.setBrush(Qt::transparent);
imgPainter.drawEllipse(32, 32, 30, 30);
imgPainter.end();
painter.drawPixmap(x, y, 64, 64, QPixmap::fromImage(fixedImage));
}
The above code does not work. The output display is not a circle shaped image.

Answer 1

I don't know if I understood correctly, but this might do what you want:
#include <QtGui/QApplication>
#include <QLabel>
#include <QPixmap>
#include <QBitmap>
#include <QPainter>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
// Load the source image.
QPixmap original(QString("/path/here.jpg"));
if (original.isNull()) {
qFatal("Failed to load.");
return -1;
}
// Draw the mask.
QBitmap mask(original.size());
QPainter painter(&mask);
mask.fill(Qt::white);
painter.setBrush(Qt::black);
painter.drawEllipse(QPoint(mask.width()/2, mask.height()/2), 100, 100);
// Draw the final image.
original.setMask(mask);
// Show the result on the screen.
QLabel label;
label.setPixmap(original);
label.show();
return a.exec();
}
Cache the result in your QWidget subclass and blit to the screen the required bounding rect in your paint event when requested.

Answer 2

You can do this relatively simply with a clipping path:
QPainter painter(this);
painter.setPen(Qt::blue);
painter.drawEllipse(30, 30, 36, 36);
QPixmap icon("./image.png");
QImage fixedImage(64, 64, QImage::Format_ARGB32_Premultiplied);
fixedImage.fill(0); // Make sure you don't have garbage in there
QPainter imgPainter(&fixedImage);
QPainterPath clip;
clip.addEllipse(32, 32, 30, 30); // this is the shape we want to clip to
imgPainter.setClipPath(clip);
imgPainter.drawPixmap(0, 0, 64, 64, icon);
imgPainter.end();
painter.drawPixmap(0, 0, 64, 64, QPixmap::fromImage(fixedImage));
(I'd cache the pixmaps if you do this often.)