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Thread: QPixmap being clipped after rotation

  1. #1
    Join Date
    Jan 2011
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    Default QPixmap being clipped after rotation

    Qt Code:
    1. QImage img("lena.jpg");
    3. rotate_image_implace(img, angle); //rotate the img with angle degrees(90, 180, 270 and so on)
    5. graph_scene_ = new QGraphicsScene(this);
    6. graph_scene_->addItem(graph_pixmap_ = new QGraphicsPixmapItem);
    7. graph_view_ = new QGraphicsView(graph_scene_, this);
    9. graph_pixmap_->setPixmap(QPixmap::fromImage(img));
    10. graph_scene_->setSceneRect(img.rect());
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    type of graph_pixmap_ is QGraphicsPixmapItem

    type of graph_scene_ is QGraphicsScene

    type of graph_view_ is QGraphicsView

    This may clip the image if their height and width are different, how could I rotate the image without clipping it?

    Because the program need to save the image after rotating and mirror(vertical and horizontal), rotation of QGraphicsPixmapItem is not adopted.

  2. #2
    Join Date
    Mar 2009
    Brisbane, Australia
    Thanked 1,592 Times in 1,520 Posts
    Qt products
    Qt4 Qt5
    Unix/X11 Windows
    Wiki edits

    Default Re: QPixmap being clipped after rotation

    You cannot rotate an x by y rectangular image without scaling and put it back into the same x by y space except in the limited case of a 180 degree rotation about the image centre. Assuming (because you have not shown us the code that you use to do this rotation) you are rotating about the centre of the x by y image then the rotated image will always fit in a square image sqrt(x*x + y*y) pixels on a side. Alternatively you can compute the minimal size of image you need to place the result in with simple trigonometry.

  3. The following user says thank you to ChrisW67 for this useful post:

    stereoMatching (25th November 2012)

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