I am using QGraphicsScene/QGraphicsView pair in my application.
I had subclassed them for my purpose. The code snippet that generate the pair is below:
itsScene = new QGraphicsScene;
itsView = new QGraphicsView;
itsView->setParent(itsCanvas);
itsView->setGeometry(20,20,1700,720);
itsView->setBackgroundBrush(Qt::black);
itsView->setAlignment(Qt::AlignTop);
itsView->setScene(itsScene);
After adding some widgets into QGraphicsScene my application final UI snapshot is below:
Here my question is why there is some free space above the picture? What may cause this?
I am using some negative coordinates for my widgets. Is it related with that?
The negative coordinates may be the cause. QGraphicsScene calculates its bounding rect from combining the bounds of all items in it.
If you know your scene bounds, call setSceneRect to fix it down to a known rect. This way graphics items placed out of the bound will not cause the scene to expand beyond what you want.
Related
I have project which display inner structure of ELF binary files. I use QGraphicsView and QGraphicsScene. So I can display blocks on graphics scene, but I need after mouse click on single block display content of this block. I am trying use function:
void MainWindow::mousePressEvent(QMouseEvent* event)
{
ui->textEdit->append(QString("x = %1, y = %2").arg(event->Pos().x()).arg(event->Pos().y()));
}
But position is tracking in whole window. Problem is, that width and height of window is dynamical and height of QGraphicsScene may be greater than window's. So I can't track single block.
I tryed some function like:
mapFromScene, mapToScene, mapFromGlobal, ... but I don't know, how theese functions works, but position what I get wasn't right.
It occurred to me that position should be calculated by scrollbar of QGraphicalView and size of window, but it's hard to calculated precisely and it's not correct solution.
Some idea, how get true position on graphic scene? Thanks for any help.
QGraphics, like other graphics frameworks, uses multiple coordinate systems and you need to consider which system you're working in when dealing with coordinates.
We can think of a QGraphicsSceneas a world, within which there are objects that are represented by QGraphicsItems ( or QGraphicsObject's. if you want them to use signals and slots).
To view an area of the world, we use one or more QGraphicsViews.
In order to map between the different coordinate systems, Qt provides the useful mapTo and mapFrom functions.
Starting at the top, with a QGraphicsView, we can convert a coordinate and use QGraphicsView::mapToScene to get the coordinate in the scene's coordinate system. From this, if an item resides at that coordinate, we can get the coordinate relative to the item, using QGraphicsItem::mapFromScene.
So, with the three levels (view, scene and item) think about which system the coordinate is in and where you want to be dealing with it.
how get true position on graphic scene?
Hopefully you should now be thinking that the coordinate you have been provided in the MainWindow is in the view's coordinate system and you can map to the scene's coordinate system.
QPointF scenePoint = mapToScene(event->Pos());
However, this is overcomplicating things and you'll find it easier to work directly with the scene and the items it contains, by overloading the item's own mouseMove/Press/Release events, which provide QGraphicsScene coordinates.
I solved this problem with make my object, which inherit QGraphicView (MyQGraphicView) and then I declared function mousePressedEvent for this object. This help me.
I'm creating 2D Map editor using opengl to draw simple 32x32 sprites but it seems that I cannot resize my QGLWidget to a large size (i.e size * sprite size -> 1024 * 32), using 1024 only seems to work fine (using glwidget->setMinimumSize(...)). I've been googling for a while now about this, the only interesting thing I found is subclassing QAbstractScrollArea and setting my QGLWidget as it's viewport (That's what QGraphicsView does), I also seen all Qt opengl examples but i couldn't find anything that could help (except Image Viewer example which is not exactly what I want), I also tried the following:
horizontalScrollBar()->setMaximum(width * 32);
verticalScrollBar()->setMaximum(height * 32);
with the widget resizable set to true/false on the scrollarea but still nothing.
Any ideas how would I do that? I can show more code if you ask me to.
Using Qt v4.7.3.
I have two ideas:
If it's possible, drop the idea of using a QGLWidget and place the sprites directly in a graphics scene (QGraphicsPixmapItem). Possibly not what you want, but the graphics scene is made to handle a lot of items, so most things you need (trigger mouse events on items for example) are already implemented.
Or just place the QGLWidget in a graphics scene using a QGraphicsWidget. This should automatically tell the scene its size, which then tells the view the size of the scene. The scroll bars appear automatically if the scene doesn't fit into the view.
Update:
As described in this link, you can use OpenGL in any graphics view:
view.setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
view.setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
I'm new to Qt development so I've being trying to research a solution to a user interface I need to design. My project is to simulate players in an online game moving around a global map. To represent the map I need to display a 2D grid, with each space in the grid representing a region of a map. I then need to display the location of each player in the game. The back-end is all fully working, with the map implemented as a 2D array. I'm just stuck on how to display the grid.
The research I have done has led me to believe a QGraphicsView is the best way to do this, but I can't seem to find a tutorial relevant to what I need. If anyone has any tips on how to implement this it would be much appreciated.
Thanks, Dan
A 2D Grid is nothing more than a set of horizontal and vertical lines. Suppose you have a 500x500 map and you want to draw a grid where the distance between the lines in both directions is 50. The sample code that follows shows you how you can achieve it.
// create a scene and add it your view
QGraphicsScene* scene = new QGraphicsScene;
ui->view->setScene(scene);
// Add the vertical lines first, paint them red
for (int x=0; x<=500; x+=50)
scene->addLine(x,0,x,500, QPen(Qt::red));
// Now add the horizontal lines, paint them green
for (int y=0; y<=500; y+=50)
scene->addLine(0,y,500,y, QPen(Qt::green));
// Fit the view in the scene's bounding rect
ui->view->fitInView(scene->itemsVBoundingRect());
You should check the QGraphicsView and the QGraphicsScene documentation as well as the corresponding examples. Also you can watch the graphics view training videos or some graphics view related videos from the Qt developer days.
Well if you have a constant grid size or even a limited number of grid sizes what i like to do is to draw a grid block in gimp or any other program and then set that as the background brush (draw only bottom and right side of the block) qt will repeat the image and will give you a full grid. I think this is good for performance too.
This is the grid image i used in one of my programs it's 10x10 pixels.
Then call QGraphicsScene setBackgroundBrush as the follwing:
scene->setBackgroundBrush(QBrush(QPixmap(":/grid/grid10.png")));
The more native way is this:
scene = self.getScene() # Your scene.
brush = QBrush()
brush.setColor(QColor('#999'))
brush.setStyle(Qt.CrossPattern) # Grid pattern.
scene.setBackgroundBrush(brush)
borderColor = Qt.black
fillColor = QColor('#DDD')
rect = QRectF(0.0, 0.0, 1280, 720) # Screen res or whatever.
scene.addRect(rect,borderColor,fillColor) # Rectangle for color.
scene.addRect(rect,borderColor,brush) # Rectangle for grid.
Sorry by PyQt...
Suppose a scene is set to the graphicsview then simply below one line will show the grid.
ui->graphicsView->scene()->setBackgroundBrush(Qt::CrossPattern);
There several other values can be passed for ex: Qt::Dense7Pattern
These are members of enum BrushStyle, just click on any used value in Qt creator and it will take you to the enum declaration where you can see all other possible values.
PS:
A scene can be set like this:
ui->graphicsView->setScene(new QGraphicsScene());
I am trying to display several images in the MainWindow and have the ability to perform certain actions when these images receive mousePressEvent.
For this, I thought I would create a new class, derived from QWidget, which had a QImage private member. With this, I as able to override the paintEvent and the mousePressEvent to both display the image and catch mouse input.
However, the problem is that the image drawn in the MainWindow has the widget size and its form (rectangular), and the image does not possess the same form (not even a regular form). This causes some problems because I am able to catch the mousePressEvent on parts that do not belong to my Image, but do belong to the Widget area.
Does anyone have any ideas on how to solve this?
I am still very new to QT, so don't please don't mind any huge mistake :)
Update:
Ok, I tried another approach.
I now have a graphicView on my MainWindow, with a graphicScene linked to it. To this scene, I added some graphicItems.
To implement my graphicItems I had to overload the boundingRect and paint method. As far as the documentation goes, my understanding is that QT uses shape method (which calls boundingRect) to determine the shape of the object to draw. This could possibly be the solution to my problem, or at least one solution to improve the accuracy of the drawn shape.
As of now, i am returning a square with my image size in boundingRect. Does anyone know how I can "adapt" the shape to my image (which resembles a cylinder)?
If you want to use QWidget you should take look at the mask concept to refine the space occupied by your images (be careful about the performance of this implementation).
If you decide to go with the QGraphicsItems you can re-implement the virtual method QPainterPath QGraphicsItem::shape () const to return a path representing as well as possible the boundary of your images.
The Qt documentation says :
The shape is used for many things, including collision detection, hit tests, and for the QGraphicsScene::items() functions.
I encourage you to go with the QGraphics system, it's sounds more appropriate in your case.
What I understand is that you want to shrink/expand/transform your image to fit a custom form (like a cylinder).
What I suggest is to use the OpenGL module QGLWidget and to map each coordinate of your rectangular image (0,0) (0,1) (1,0) (1,1) to a custom form created in OpenGL.
It will act as a texture mapping.
Edit: you can still catch mouse input in OpenGL
I subclassed QGraphicsItem and reimplemented paint.
In paint I wrote something like this for labeling the item:
painter->drawText("Test",10,40);
After some time I think It may be useful to handle labeling with seperate item. So I wrote something like this.
QGraphicsTextItem *label = new QGraphicsTextItem("TEST",this);
setPos(10,40);
But two "TEST" drawing do not appear in the same place on screen. I guess difference may be related with item coordinates - scene coordinates. I tried all mapFrom... and mapTo... combinations inside QGraphicsItem interface but no progress. I want to drawings to appear in the same place on screen.
What I miss?
I assume that you are using the same font size and type in both cases. If the difference in position is very small the reason can be the QGraphicTextItem is using some padding for the text it contains. I would try to use QGraphicsSimpleTextItem that is not going to add fancy stuff internally and see if you still have the same problem. The coordinates system is the same one if you use painter or setPost so that is not the problem. If this doesn't help I will suggest to specify the same rect for both to avoid Qt adding it owns separation spaces.