I have a problem, i'm developing a graphical program under Windows, there are few QGraphicsScene and one QGraphicsView that it is possible to change the Scenes in runtime with a lot of graphics items, the problem is when I use Qwidget viewport everything works but when I switch to OpenGL viewport when I change the scene the content of previous scene still appear on the QGraphicsView and the contents of new Scene appear too.
what is the problem ? is it the changing Scenes method best solution or should I change the method ?
here is the code to setup View
m_viewPort = new QOpenGLWidget (this);
QSurfaceFormat format;
format.setProfile(QSurfaceFormat::CoreProfile);
format.setDepthBufferSize(24);
format.setStencilBufferSize(8);
format.setSamples(4);
m_viewPort->setFormat(format);
ui->gV->setViewport(m_viewPort);
ui->gV->setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
//ui->gV->setCacheMode(QGraphicsView::CacheBackground);
ui->gV->setRenderHints(QPainter::Antialiasing| QPainter::HighQualityAntialiasing | QPainter::SmoothPixmapTransform| QPainter::TextAntialiasing);
ui->gV->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
ui->gV->setVerticalScrollBarPolicy (Qt::ScrollBarAlwaysOff);
ui->gV->setTransformationAnchor(QGraphicsView::NoAnchor);
ui->gV->setAutoFillBackground(false);
ui->gV->setAttribute(Qt::WA_OpaquePaintEvent, true);
ui->gV->setAttribute(Qt::WA_NoSystemBackground, true);
resize(boardBaseSize);
here is code to set the new scene to the view
void GlScreenBoard::setShowScene(QGraphicsScene *scene, QString programName)
{
scene->setSceneRect(boardSceneRectBase);
ui->gV->setScene(scene);
}
another problem is when I set Graphics view CacheMode to CacheBackground the OpenGL viewport disables !! and the painter in QGraphicsScene returns to Raster !
Related
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.
I re-implemented QGraphicsView to have the scene zoomed with a mouse wheel event. The scene contains several QGraphicsPixmapItem. The wheel event calls QGraphicsView::scale(qreal sx, qreal sy)
Everything works perfectly but the rendering. As I zoom out (the scene gets smaller), aliasing appears. I tried setting the render hints as following in the re-implemented QGraphicsView constructor:
ImageViewer::ImageViewer(QWidget * parent) :
QGraphicsView(parent)
{
setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform | QPainter::HighQualityAntialiasing);
}
I still see these artifacts. How can I get rid of this ?
Please see my comments for this question.
Basically you have to call setTransformationMode(Qt::SmoothTransformation) on the QGraphicsPixmapItems you want anti-aliasing to apply to.
Calling setRenderHints on the view did not work for me, either.
The render hints are only applied if it is set bevor the painter is used. Here a snipped:
QGraphicsPixmapItem *
drawGraphicsPixmapItem(const QRectF &rect)
{
auto pixmap = new QPixmap(rect.size().toSize());
pixmap->fill("lightGrey");
auto painter = new QPainter(pixmap);
// set render hints bevor drawing with painter
painter->setRenderHints(QPainter::Antialiasing);
QPen pen;
pen.setColor("black");
pen.setWidth(3);
painter->setPen(pen);
QRectF rectT = rect;
rectT.adjust(pen.widthF()/2,pen.widthF()/2,-pen.widthF()/2,-pen.widthF()/2);
QPainterPath circlePath;
circlePath.addEllipse(rectT);
circlePath.closeSubpath();
painter->fillPath(circlePath,QBrush("green"));
painter->drawPath(circlePath);
auto pixmapItem = new QGraphicsPixmapItem(*pixmap);
pixmapItem->setCacheMode(
QGraphicsItem::CacheMode::DeviceCoordinateCache,
pixmap->size() );
return pixmapItem;
}
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 am using Qt and I want to display a image and I am displaying it in QGraphicsView and as the image is bigger than the dimensions of box of the QGraphicsView I used
ui->graphicsView->fitInView(viewraw->itemsBoundingRect() ,Qt::KeepAspectRatio);
where viewraw contains pixmap address to my image, my problem of oversized image was solved with this but my new problem now is the image after automatic resizing by Qt now shows with very very bad quality, it is very very blurry
What should I do?
Is there any way to display the image fit in the box and no quality loss?
Thank you!
You should try enabling antialiasing:
ui->graphicsView->setRenderHints(QPainter::Antialiasing
| QPainter::SmoothPixmapTransform
| QPainter::TextAntialiasing);
You can use QLayout::setSizeConstraint(QLayout::SetFixedSize) on the layout containing the view, to resize the parent widget to fit the view. The size will be the one returned by the view sceneRect() function.
For example, the following code will resize the QMainWindow (and lock the size) so that both items are visible:
#include <QtGui>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QMainWindow mainWindow;
QGraphicsView *view = new QGraphicsView(&mainWindow);
QGraphicsScene *scene = new QGraphicsScene(view);
view->setScene(scene);
mainWindow.layout()->setSizeConstraint(QLayout::SetFixedSize);
mainWindow.setCentralWidget(view);
mainWindow.show();
scene->addRect(-100,-100,10,10, QPen(), Qt::red );
scene->addRect(600,450,10,10, QPen(), Qt::blue );
return a.exec();
}
Or, since you are using the designer,
in the widget tree, go to the parent item of the graphics view, it should have a layout,
if not (if the icon is this one: ), add one by left clicking on the item name and choose a layout in the "Lay Out" menu (if you only have one widget, the type of layout doesn't matter, just choose one),
then go to the last option in the property panel for the same item, which should be "layoutSizeConstraint" and select the option "SetFixedSize".
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