How to detect collision between two QGraphicsPixmapItems if the pixmaps' edges are transparent?

Question

I have two QGraphicsPixmapItems, the edges of both are transparent and they aren't rectangle shaped. When I try to use QGraphicsItem::collidingItems(), it only checks if their bounding rects are colliding. Is there a way to detect the collision only of the non-transparent parts?

Answer 1

You must set the shape mode to QGraphicsPixmapItem::HeuristicMaskShape:

QGraphicsPixmapItem::HeuristicMaskShape

The shape is determine by calling QPixmap::createHeuristicMask(). The performance and memory consumption is similar to MaskShape

---

your_item->setShapeMode(QGraphicsPixmapItem::HeuristicMaskShape);

Example:

main.cpp

#include <QApplication>
#include <QGraphicsPixmapItem>
#include <QGraphicsView>

#include <QDebug>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QGraphicsView w;
    QGraphicsScene *scene = new QGraphicsScene;
    w.setScene(scene);

    QList<QGraphicsPixmapItem *> items;

    for(const QString & filename: {":/character.png", ":/owl.png"}){
        QGraphicsPixmapItem *item = scene->addPixmap(QPixmap(filename));
        item->setShapeMode(QGraphicsPixmapItem::HeuristicMaskShape);
        item->setFlag(QGraphicsItem::ItemIsMovable, true);
        item->setFlag(QGraphicsItem::ItemIsSelectable, true);
        items<<item;
    }

    items[1]->setPos(50, 22);
    if(items[0]->collidingItems().isEmpty())
        qDebug()<<"there is no intersection";
    w.show();
    return a.exec();
}

output:

there is no intersection

The complete example can be found in the following link