I'm using QtLocation QML Map to display a big amount of items on a map. As with the number of items visible on the map the performance decreases, i would like to set visible only the items actually visible on the viewport. For this it would be handy to just calculate the visibility based on whether the item's coordinate is within the viewport, like:
visible: mapBase.visibleRegion.contains(model.item.coordinate)
But unfortunately the visibleRegion property is non-NOTIFYable, as stated in the documentation at http://doc.qt.io/qt-5/qml-qtlocation-map.html#visibleRegion-prop.
Is there any specific reason (like performance-issues) to not implement a notify signal for this property? Is there any way to workaround this, and set the visibility of a map item based on whether it's within the viewport?
I suppose the reason could be that it's expensive to calculate.
But visibleRegion changes when one of the following properties change: zoomLevel, center, bearing, tilt, fieldOfView. You could, for example, define your own "property var visRegion", and update it when reacting on those properties above by fetching visibleRegion and assigning it to visRegion.
Related
I have a set of controls which have bindings to frequently changing data values. The data comes from a limited hardware-bus. Therefore, it would be better to disable the binding while the control is not visible on screen. The item's visible-property doesn't help in this case. So, how to determine if an Item-based QML widget is currently visible on screen (and not hidden by an overlay or currently outside the visible area)?
Source: https://forum.qt.io/topic/54116/how-to-check-if-a-item-is-currently-visible-on-screen
I have almost the same problem. Hoping someone here has a solution.
Here's what I would try to get working:
First, I presume there is a ScrollView or Flickable in play here? If so, then hook to signals like Flickable::movementEnded().
Second, when that signal fires, use Item::mapToItem() to check if each of your Item's visible rectangle (based on x, y, width, height) intersects your window's contentItem rectangle. Set the result as a boolean on each of your items and make sure the data retrieval is disabled when it is false (using && or a tertiary JS expression).
Or if more convenient, remove the binding when false and reapply it with Qt.binding() when true.
I need to access currently visible rows (first, last) from a JavaScript function, that is defined inside a TableView.
TableView
{
function getVisibleRows()
{
...
}
}
I see that ListView (what is a Flickable) has a contentY property which would make the problem trivial, but TableView has not. Also, TableView is implemented in terms of a ListView, so there is a ListView involved, but I am not sure how to access it.
Thank You!
I've figured out. I simply need to access flickableItem.contentY.
Use the viewport property of Scrollview (inherited by TableView), which
determines the current "window" on the contentItem. In other words, it
clips it and the size of the viewport tells you how much of the
content area is visible.
viewport return a complete qml item so you can get a lot of position data.
The documentation for the QGraphicsItem::ItemIgnoresTransformations flag says
The item ignores inherited transformations (i.e., its position is still anchored to its parent, but the parent or view rotation, zoom or shear transformations are ignored). This flag is useful for keeping text label items horizontal and unscaled, so they will still be readable if the view is transformed. When set, the item's view geometry and scene geometry will be maintained separately. You must call deviceTransform() to map coordinates and detect collisions in the view. By default, this flag is disabled. This flag was introduced in Qt 4.3. Note: With this flag set you can still scale the item itself, and that scale transformation will influence the item's children.
Of course I have read the QGraphicsItem details, the QGraphicsScene details, the QGraphicsView details, and the Graphics View Framework.
There are also several questions about the ItemIgnoresTransformations flag like Fixed size QGraphicsItems in multiple views?
But I still do not understand the sentence in bold face. What does it mean ?
The problem that rose this concern is described in PyQt: Moving multiple items with different ItemIgnoresTransformations flags, but maybe this question was too long, or too pyqt oriented at first sight. And it was more about moving items. So here I'm trying to better focus.
Imagine situation that parent is rotated 45 degrees or even have some sheer. Since current item ignores this transformation it stays strait (not rotated).
Now ask question how this impacts on item size and position? Parent may maintain geometry of item (for example by using layout) but it doesn't take into account this flag, so some geometry (which is in parent units) will be set but effectively items scene rect may appear different since item ignores transformation and it is not rotated squeezed zoomed as a parent.
So from parent point of view geometry has some value but form scene point of view it is different.
It would be best if you try to see how it works in practice It is hard to describe problem clearly.
I created a sketchUp plugin that draws a wall (with lenght, width and height).
Now I would like to insert a "window" in that wall (fixed length, width and height, depending on the wall). How can I:
Create but not yet draw the group containing the window. Link it to the current mouse position
Constrain the current mouse position to the front plane of the wall I drew before
When the user clicks, the window is inserted and the group is shown
The easy way to do it, that doesn't fulfill your request 100% - but do use existing SketchUp conventions, is to create a component definition and then use Model.place_component to activate SketchUp's native tool to position a new component instance.
In order to fulfill your question 100%:
A Group is an instance. You cannot create one and not place it in the model. You can create it in step 3 when the user clicks. (Though, a window sounds like a candidate for a component since you usually have multiple copies of the same window type.)
You cannot constrain the mouse cursor itself, but if you implement a custom Tool and make use of the InputPoint class you can selectively determine what is a valid insertion point when the user clicks. You can also draw virtual lines and polygons to the viewport to give a preview of your window.
Profit!
Hi i'm trying to get a photoshop-like behaviour for my QGraphicsScene
The grid in the background should not resize with the call of scale. And I must be able to save the picture with QPixmap::grabWidget(view) but without the background grid. I can probably do it with removing the background layer just before saving the picture, but i'm not sure if its cleanest way to do it.
Any ideas ?
thx.
Question 1
The grid in the background should not resize with the call of scale.
Use the QGraphicsItem::ItemIgnoresTransformations flag.
The item ignores inherited transformations (i.e., its position is
still anchored to its parent, but the parent or view rotation, zoom or
shear transformations are ignored). This flag is useful for keeping
text label items horizontal and unscaled, so they will still be
readable if the view is transformed. When set, the item's view
geometry and scene geometry will be maintained separately.
In order to set this flag use the setFlag function when creating the grid item.
Question 2
I must be able to save the picture with QPixmap::grabWidget(view) but without the
background grid.
Call the hide function on the grid item before calling the grabWidget. After you have grabbed it you show it again by calling the show function.