Qt zoom example

QLabel is typically used for displaying text, but it can also display an image. QScrollArea provides a scrolling view around another widget. If the child widget exceeds the size of the frame, QScrollArea automatically provides scroll bars. The example demonstrates how QLabel 's ability to scale its contents QLabel::scaledContentsand QScrollArea 's ability to automatically resize its contents QScrollArea::widgetResizablecan be used to implement zooming and scaling features.

In addition the example shows how to use QPainter to print an image. With the Image Viewer application, the users can view an image of their choice. The File menu gives the user the possibility to:. In addition the Help menu provides the users with information about the Image Viewer example in particular, and about Qt in general. We reimplement the constructor, and create several private slots to facilitate the menu entries.

In addition we create four private functions.

qt zoom example

We use createActions and createMenus when constructing the ImageViewer widget. We use the updateActions function to update the menu entries when a new image is loaded, or when the Fit to Window option is toggled. The zoom slots use scaleImage to perform the zooming. In turn, scaleImage uses adjustScrollBar to preserve the focal point after scaling an image.

We set imageLabel 's size policy to ignoredmaking the users able to scale the image to whatever size they want when the Fit to Window option is turned on. Otherwise, the default size polizy preferred will make scroll bars appear when the scroll area becomes smaller than the label's minimum size hint. We ensure that the label will scale its contents to fill all available space, to enable the image to scale properly when zooming.

If we omitted to set the imageLabel 's scaledContents property, zooming in would enlarge the QLabelbut leave the pixmap at its original size, exposing the QLabel 's background. We make imageLabel the scroll area's child widget, and we make scrollArea the central widget of the QMainWindow.

At the end we create the associated actions and menus, and customize the ImageViewer 's appearance. In the open slot, we show a file dialog to the user. We compile a list of mime types for use as a filter by querying QImageReader for the available mime type names. For files in JPEG format, this ensures that portrait mode images of digital cameras are shown correctly by applying the appropriate orientation read from the EXIF meta data stored in the image file. We then load the image using QImageReader::read.

If this returns a null image, indicating that the file is not an image file, we use a QMessageBox to alert the user. The QMessageBox class provides a modal dialog with a short message, an icon, and some buttons. QMessageBox provides a range of different messages arranged along two axes: severity question, information, warning and critical and complexity the number of necessary response buttons.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. And I want to connect that to the mouse wheel just like in the normal browsers when you can zoom in and out by pressing the 'ctrl' key and turning the mouse wheel.

Is there a default function for that?

QML Maps with Pinch Zoom

I tried searching for some examples but without any luck. So how can I do that? Learn more. Zooming function on a QWidget Ask Question. Asked 9 years ago. Active 9 years ago. Viewed 16k times. Raiv 5, 1 1 gold badge 30 30 silver badges 50 50 bronze badges. May be consider using QScrollArea. Please take a look at stackoverflow.

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Active Oldest Votes. Try to reimplement your paintEventand apply scale to QPainter before drawing. Raiv Raiv 5, 1 1 gold badge 30 30 silver badges 50 50 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook.

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Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I'm trying to use a QML Scale Element to perform view scaling around a point clicked by the user, but it's not always working as documented. My goal is to have it always zoom correctly maintaining the click point as the origin, as stated in the documentation.

Interestingly, if you now click again in the center of the red rectangle, it scales up around that point as promised. Clicking again now on the center of the blue rectangle, you see the same unexpected translation behaviour.

Many applications have exactly this behaviour. See for example inkscape. I filed this as a Qt bug, because the behaviour does not follow the documentation.

At the moment of writing, the bug seems to have been triaged as "important". In fact it is not a deviant behavior, just a different one from what you may expect after reading the doc.

When you change the Scale transform of your rectangle, the transformation is applied on the original rectangle. The point you click on stay in the same place from the original rectangle point of view. That's why your rectangle "moves" so much when you click on one corner then the opposite corner.

In order to achieve what you want, you can't rely on transform origin. You have to set the actual x y coordinates of your rectangle.

Learn more.

qt zoom example

Asked 6 years ago. Active 3 years, 6 months ago. Viewed 6k times. See that everything is scaled up, but the center of the blue rectangle remains at your click location. See that everything is scaled up, but the center of the red rectangle did not remain at your click point, it was translated up and to the left.

This is not as documented. Controls 1. MBach 1, 13 13 silver badges 27 27 bronze badges. Charl Botha Charl Botha 3, 27 27 silver badges 46 46 bronze badges. What is the expected behaviour? It's not clear what you want to happen.

When you click in the centre of a coloured rectangle, it should increase in size symmetrically around that point. This works when you click the first rectangle, but gives unwanted behaviour when you click the centre of the other one for the first time. I'll expand my question to explain this better. The problem is clear when you try the example. I did try the example, and it was still unclear to me.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I have a window, in which is a QGraphicsView, which will be displaying an image.

I have implemented the wheelEvent. My images are mostly going to be bigger than the window, so I get scroll bars in the window.

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What we normally observe when we rotate the wheel while viewing an image in Windows Photo Viewer is that when we move the wheel up towards it's wirethe image zooms in and when we move it down towards out bodythe image zooms out.

What I am getting instead is when I move the wheel towards myself to zoom out the image instead of zooming outfirst scrolls down, and starts zooming out only when the scroll bar touches its bottom most point.

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It would be better to understand the problem by trying out the code. I am not able to explain in I guess. The code shows that you didn't subclass QGraphicsViewbut instead use one in your own widget. The wheel event will be first sent to the actual graphics view widget. There it is handled with Qt's default behaviour, namely scrolling. Only if you scrolled to the bottom, the graphics view cannot handle the wheel event, and it is propagated to its parent, your class.

That's why you only can zoom when scrolled to the border. To fix this, you should install an event filter. That allows you to intercept the wheel event and process it in your class:.

Update I just figured out that the event filter will not recieve GraphicsSceneWheel events on the graphics view. Instead, you have to install the filter on the Graphics Scene. Learn more. Qt 5 : Mouse Wheel event behaviour for zooming image Ask Question. Asked 4 years, 5 months ago. Active 4 years, 5 months ago. Viewed 9k times. I want the standard behavior.

What to do? Code include "viewer. Nancy Nancy 4 4 silver badges 13 13 bronze badges. With propagate I mean that events are handled in a chain. When an event is sent to a widget that does not handle it e. Wheel events on Push Buttonsit will be propagated to its parent widget so it can handle it e.

Qt Tutorial: Unit 15, QLineEdit, Input-Masks and Validators

The same is for event filters. See also: stackoverflow. Active Oldest Votes. I made some changes to the code. Now my image doesn't scroll at all. It only moves up and down on scrolling the wheel.QwtPlotZoomer provides stacked zooming for a plot widget. QwtPlotZoomer selects rectangles from user inputs mouse or keyboard translates them into plot coordinates and adjusts the axes to them.

The selection is supported by a rubber band and optionally by displaying the coordinates of the current mouse position. Zooming can be repeated as often as possible, limited only by maxStackDepth or minZoomSize.

Each rectangle is pushed on a stack. The default setting how to select rectangles is a QwtPickerDragRectMachine with the following bindings:. The setKeyPattern and setMousePattern functions can be used to configure the zoomer actions. The following example shows, how to configure the 'I' and 'O' keys for zooming in and out one position on the zoom stack. The "Home" key is used to "unzoom" the plot.

qt zoom example

QwtPlotZoomer is tailored for plots with one x and y axis, but it is allowed to attach a second QwtPlotZoomer without rubber band and tracker for the other axes. The zoomer is set to those x- and y-axis of the parent plot of the canvas that are enabled. If both or no x-axis are enabled, the picker is set to QwtPlot::xBottom. If both or no y-axis are enabled, it is set to QwtPlot::yLeft. Reimplemented from QwtPicker. Rejects selections, when the stack depth is too deep, or the zoomed rectangle is minZoomSize.

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Expand the selected rectangle to minZoomSize and zoom in if accepted. Reimplemented from QwtPlotPicker.

Adjust the observed plot to zoomRect. A value of -1 set the depth to unlimited, 0 disables zooming. If the current zoom rectangle is below depth, the plot is unzoomed. Reinitialized the zoom stack with scaleRect as base. In combination with other types of navigation it might be useful to modify to manipulate the complete zoom stack.

Clears all rectangles above the current position of the zoom stack and pushes the normalized rectangle on it. Activate a rectangle on the zoom stack with an offset relative to the current position. Negative values of offset will zoom out, positive zoom in.

A value of 0 zooms out to the zoom base. A signal emitting the zoomRectwhen the plot has been zoomed in or out.

qt zoom example

The default setting how to select rectangles is a QwtPickerDragRectMachine with the following bindings: QwtEventPattern::MouseSelect1 The first point of the zoom rectangle is selected by a mouse press, the second point from the position, where the mouse is released. QwtEventPattern::KeySelect1 The first key press selects the first, the second key press selects the second point. Create a zoomer for a plot canvas. This might be necessary, when the plot is in a state with pending scale changes.

Check and correct a selected rectangle. Returns true If the rectangle is accepted, or has been changed to an accepted one. Parameters ok If true, complete the selection and emit selected signals otherwise discard the selection. Returns Maximal depth of the zoom stack.Your browser does not seem to support JavaScript. As a result, your viewing experience will be diminished, and you may not be able to execute some actions. Please download a browser that supports JavaScript, or enable it if it's disabled i.

I want to be able to zoom my QGraphicsView or the QGraphicsScene by dragging with two fingers, just as it's usual with touch devisces, because I want to optimize the application for touch displays. Is there something already existing in Qt that makes this easy? Thanks for answers! I can't find this example in Qt Creator Examples Niagarer Hi That's odd. Niagarer said in QGraphicsView touch zoom :.

Qt Documentation

Niagarer You can open the examples by navigating to them from File menu. I navigated to the Qt5. I'm sorry, that this is drifting away from the actual question.

Niagarer Ok, i just tried the sample here. Qt Creator seems to have bad days somethimes. Thanks anyway! The zoom works, but there is a problem. In the example, the transform of the view itself is just changed. But proxywidgets placed in the scene get scaled too when changing transform. What I need is some kind of scale that does not effect the scale of the proxys in the scene. The proxys shall always be in the same viewport position.

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