I'm working on a Qt application made with a main QGraphicsView.
This view can show and switch between differents QgraphicsScenes. This application needs to always have an overlay in front of each scenes, so the best way to do this overlay is by setForegroundBrush() method of QGraphicsView.
But my overlay is a tiled-image, where I could edit the opacity and the scale of the source image.
Here's the code written in my QGraphicsView class constructor :
QString imgPath("path/to/image.png");
QPixmap map(imgPath);
QPainter painter(this);
QRectF zone(0,0,map.width(),map.height());
painter.drawPixmap(zone,map,zone);
QBrush brush = painter.brush();
brush.setStyle(Qt::TexturePattern);
setForegroundBrush(brush);
But doesn't work, nothing is shown.
I tested a simple QBrush with a QPixmap and works fine, but I need to use QPainter to be able to edit the opacity of my image.
Finally I think the easiest way to have a tiled image in QGraphicsView foreground is by reimplmenting the drawForeground(QPainter *painter, const QRectF &rect).
void Frontend::drawForeground(QPainter *painter, const QRectF &rect){
float alpha = 0.15;
float scale = 2;
QString imgPath("path/to/image.png");
QPixmap img(imgPath);
painter->scale(scale,scale);
painter->setOpacity(alpha);
painter->drawTiledPixmap(rect,img);
}
You cannot paint on the widget outside of its paintEvent method. Perhaps you wanted to have the painter work on the pixmap (painter(&map)) instead of the widget (painter(this))?
You could also add an overlay by:
Painting it in the reimplemented paintEvent of your derived scene, making sure that you paint not on the scene, but on its viewport(). There are convenience methods that are called by the view's paintEvent, such as drawBackground and drawForeground.
Painting it in a generic QWidget overlay.
I have several answers that demonstrate how to get overlays over widgets in generaly, and also on scene views.
Related
I'm new to Qt and I'm having some problem with QWidget rotation.
I have a QPixmap inside a QLabel.
What I want is to animate it with a continuous rotation by 90 degrees.
I know QPropertyAnimation and I know how to use it, but I'm struggling with How to use it for rotating a QWidget. Is there any simple way to use achieve my goal and rotate the entire QLabel or the QPixmap inside it with an animation?
Thank you.
This is the demo for rotation of QLabel/QPixmap with animation.
it's not necessary to use QPropertyAnimation. Because there is no rotate property for QLabel or QPixmap. So used QVariantAnimation make QPixmap rotate as animation and use QPixmap::transformed to rotate it. If you want well to control the animation of the pixmap, highly recommend QGraphicsPixmapItem with QPropertyAnimation
class RotateMe : public QLabel {
Q_OBJECT
public:
explicit RotateMe(QWidget* parent = Q_NULLPTR) :
QLabel(parent),
pixmap(100, 100),
animation(new QVariantAnimation )
{
resize(200, 200);
pixmap.fill(Qt::red);
animation->setDuration(10000);
animation->setStartValue(0.0f);
animation->setEndValue(90.0f);
connect(animation, &QVariantAnimation::valueChanged, [=](const QVariant &value){
qDebug()<<value;
QTransform t;
t.rotate(value.toReal());
setPixmap(pixmap.transformed(t));
});
animation->start();
}
private:
QPixmap pixmap;
QVariantAnimation *animation;
};
You can implement the rotation in two ways:
1) Create a collection of static images each of which represents the original pixmap rotated by some angle. With a timer you can change your label's pixmap with one from your collection. This will imitate the animated rotation.
2) Use a single pixmap and override your label's QLabel::painEvent() where you should rotate the QPainter object with QPainter::rotate() function each time you redraw the label.
I would like to have certain things drawn on QGraphicsScene, but not be QGraphicsItem (it would interfere with the processing of the QGraphicsItem collection).
Example: a scene bounding rectangle, a grid
I am overriding the drawBackground(QPainter *painter, const QRectF &rect) for that purpose. (I should subclass the scene... )
void MyView::showHideBounds()
{
m_showBackgroundBounds = !m_showBackgroundBounds;
// can't triger an update ???
update(); // neither does anything
viewport()->update();
}
void MyView::drawBackground(QPainter *painter, const QRectF &rect)
{
QPen pen;
if(m_showBackgroundBounds)
pen = QPen(QColor(0, 0, 0), 10, Qt::PenStyle(Qt::SolidLine));
else
pen = QPen(QColor(255, 255, 255), 10, Qt::PenStyle(Qt::SolidLine));
painter->setPen(pen);
painter->drawRect(QRect(QPoint(-scene()->sceneRect().size().toSize().width()/2,
-scene()->sceneRect().size().toSize().height()/2),
scene()->sceneRect().size().toSize()));
}
I would like the option to show/hide either the bounding rectangle or the grid.
The only thing I can think of is paint over them with the color of the background brush ? Is there any other option ?
As I have written it above, it works - except I need user action on items (or a zoom or some other scene changing action) to trigger refresh, or call an update... (the function showHideBounds doesn't - not sure how to make it force a refresh)
I would call the drawBackground from the showHideBounds function - but I don't know how to get the painter
[Also, the drawBackground seems to be drawn automatically... how can I give it the rect argument it needs ? (it seems if I draw the rect it does draw the scene rectangle but I only see the right and bottom edges)]
In order to redraw a particular section of scene, you can call
QGraphicsScene->invalidate(rect_to_redraw, Backgroundlayer)
Note that if drawBackground(*painter, rect) paints over area outside rect, it will not update automatically. In that case invalidate has to be called with appropriate rect parameters.
Here is another newbie to Qt.
What I need to do is to have a scrollable Area in the center of MainWindow, which displays images, and allows user to paint on the image.
Since I cannot add a QPixmap directly to a scrollable Area, I tried to create a subclass of QWidget, like below:
class Canvas: public QWidget
{
public:
Canvas(){
image = new QPixmap(480,320);
image->fill(Qt::red);
}
QPixmap *image;
};
Then I declared Canvas *c in the header file.
In the implementation, I wrote:
canvas = new Canvas;
setCentralWidget(canvas);
However, apparently this does not help to show up the QPixmap. I do not know what to do.
You don't need to subclass QWidget for this. QPixmap is not a widget, so it is not shown anywhere. You need to add your pixmap to some widget, this will work:
in header:
QLabel* imageLabel;
in cpp:
imageLabel = new QLabel(this);
QPixmap image(480,320);
image.fill(Qt::red);
imageLabel->setPixmap(image);
setCentralWidget(imageLabel);
I want to redefine the QPainter before drawing earch QGraphicsItem in a QGraphics scene.
void GraphicsScene::drawItems( QPainter * painter, int nbItem, QGraphicsItem *[] items, const QStyleOptionGraphicsItem[] options, QWidget * widget = NULL )
Is now obsolete, what's the "new" method ?
Thx
The QGraphicsScene isn't in charge of the painter... it is in charge of the storage and retrieval of the items. The QGraphicsView is in charge of the painter and transformation of the view.
If you want to set render hints to modify the QPainter behavior, you can do that from the view using QGraphicsView::setRenderHint.
If you just want to do a single render to another special QPainter engine, the documentation shows an example for it to a printer here.
Here is link to the docs on QGraphicsView.
I have a QGraphicsView and a QGraphicsScene connected like this:
graphicsScene->setSceneRect(this->graphicsView->rect());
graphicsView->setScene(this->Scene);
Then I load an image and add it to the scene:
QPixmap pixmap;
pixmap.load(fileName);
pixmap = pixmap.scaled(this->graphicsView->size());
QGraphicsPixmapItem* item = this->Scene->addPixmap(pixmap);
Now, as described in the documentation, the image corner is at (0,0), which is not the corner of the graphicsScene. I know I can position the resulting pixmap by doing:
item->setPos(this->Scene->sceneRect().x(), this->Scene->sceneRect().y());
However, I can't seem to make sense of the coordinates of the rect's of the scene or the view. Can anyone explain how I would move the pixmap to the corner of the scene/view?
Thanks,
David
EDIT: Here is the full form constructor. The QGraphicsView was created in Qt Designer and is inside of a GridLayout:
Form::Form(QWidget *parent)
: QWidget(parent)
{
setupUi(this);
QGraphicsScene* scene = new QGraphicsScene;
scene->setSceneRect(this->graphicsView->rect());
this->graphicsView->setScene(scene);
QPixmap pixmap;
pixmap.load("image.png");
pixmap = pixmap.scaled(this->graphicsView->size());
scene->addPixmap(pixmap);
}
I also tried this:
QGraphicsScene* scene = new QGraphicsScene;
this->graphicsView->setScene(scene);
QPixmap pixmap;
pixmap.load("/home/doriad/glasses.jpg");
QGraphicsPixmapItem * item = scene->addPixmap(pixmap);
this->graphicsView->fitInView (item);
but the image appears tiny, rather than filling up the view like I would expect. Can anyone explain this?
The full project and image are available here: daviddoria.com/Uploads/qt/QPixmapPosition
Don't worry about scaling the pixmap yourself or even translating it, let the view do it for you.
Use graphicsView->fitInView(pixmap); but you should read the documentation for :
Qt's Graphics View Framework
void QGraphicsView::setSceneRect (QRectF )
void QGraphicsView::translate ( qreal dx, qreal dy )
void QGraphicsView::fitInView ( const QGraphicsItem * item, ... )
The way that QGraphicsScene and QGraphicsView interact is that you can have a single scene with at least one or more views.
A good example I like to think of is a zoomed in view of part of a map with a mini view of the entire map in the corner. There are two views, one of part of the map and one of the entire map, with one scene, the map itself.
So you put items in your scene and all the items in the scene are drawn relative in size to each other. The "scene rect" of your view, by default, scales to fit the items in the view until one unit in the scene is one pixel in the view or until it needs to zoom out to fit all the items in your scene.
If you call fitInView(someItem) it should scale your view of the scene so that the item specified fills it up and translates the view so that it is centered. If you need to translate or scale it more use the translate or scale functions in QGraphicsView.
When you are jumping between coordinate systems of your scene and view with your QRect's or QPoint's, use the helper functions: mapToScene and mapFromScene from QGraphicsView.
Try this:
QGraphicsScene* scene = new QGraphicsScene;
scene->setSceneRect(graphicsView->sceneRect());
QPixmap pixmap;
pixmap.load("/home/doriad/glasses.jpg");
pixmap=pixmap.scaledToWidth(this->graphicsView->width());
QGraphicsPixmapItem * item = scene->addPixmap(pixmap);
graphicsView->setScene(scene);
By default, the pixmap will be at (0,0) in the scene, and the scene will be at (0,0) in the view. QWidgets are sized by pixels. If you had a QGraphicsView the size of the screen and the resolution is 1440 x 900, you can position objects in that view from (0,0) or the top left corner of the screen, to (1440,900) the bottom right corner of the screen. Most QGraphicsItems are placed with reference to their top left corner. So placing a pixmap at (0,0) aligns the top left corner of the pixmap with the top left corner of the scene it's placed in. If your pixmap 'hangs off the bottom' of your view, try using:
pixmap=pixmap.scaledToHeight(this->graphicsView->height());
If you use the function:
this->graphicsView->fitInView (item);
The graphicsView will only scroll to the point where your item fits in the view.
I downloaded David's code and ran it two ways. Click the links to see the results.
1) with pixmap=pixmap.scaledToHeight(this->graphicsView->height());
2) with pixmap=pixmap.scaledToHeight(200);
I don't know enough to explain why this is happening, but I thought it would be a useful data point.
It turns out the problem was that the GraphicsView was in a layout. In my example, the resizing of the image was done in the Form constructor. Apparently this is before the layout takes its shape? I moved the code to a pushButton and when I click it the image is sized how I would expect.
I got the image to stay sized to the GraphicsView in the Layout by subclassing QGraphicsView and reimplementing :
class CustomGraphicsView: public QGraphicsView
{
Q_OBJECT
{
void resizeEvent ( QResizeEvent * event )
{
emit resized();
}
signals:
void resized();
}
Then I connect this resized() signal to a slot that simply calls this->View->fitInView (this->ImageToTraceItem);
David