I need to implement a simple sound editor with a specific signal processing function.
I want to display the sound information vertically as a large picture - 1024 x [large height].
So I'm looking for Qt's best way to implement low-cpu-consuming vertical scrolling similar to web-browsers scrolling.
You need to create a custom widget by overriding it's paintEvent().
Have a look at this self-explanatory example on how to create a following widget.
A normal QScrollArea will give you what you want 99% of the time. But you're wanting to create a bitmap of potentially massive size, and you want to store it in RAM - you will quickly run out of space.
You are probably going to need a need a system where you save the image to file, and use the scroll area's bounds to intelligently load it's contents from the file (and a certain size around it to make it smooth) - Qt does not provide this. This is hardly groundbreaking stuff, so a web search for "scrolling very large images" or something similar should give a smart result.
If your intention is to plot STFT data, then you can easily adopt one of the widgets in the QWT library:
http://qwt.sourceforge.net/
Anyway, take a look at it, it is a great source of inspiration and the code is available...
Related
I am trying to make a simple QT android app, but basically my problem is that on my main screen I have about 250 little images that i want to scroll. But I really need the scrolling to be fluent and fast. First I tried it using QML but it wasnt really fast, then I tried to make the app in qt designer and use widgets but that was very slow. Then I tried using openGL but on android I can only use openGL ES and I cant find so much examples because every example that I find is much more advanced than I need.
But basically my main question is, what do you think is the best way to solve my problem and if its openGL which way of using it is the best that could solve it?
Thank you.
Neither approach should have problems when scrolling when compared to a native application on the same device. Check the following:
Make sure to measure performance only in release-builds, with QML debugging disabled and no debugger attached.
Maybe your device simply can't keep up with so many images in one view - then it's not a Qt problem. Compare with a 'native' java-App to see if this is the case.
Check if you implemented everything correctly; e.g. check if theres anything running in your main-loop or some events happenening repeatedly which consumes CPU time
And some more general advice:
Downscale your images to the appropriate view-size before giving them to the UI, as they might have to be re-scaled on every frame-update and/or consume graphics memory otherwise. E.g. dont set the source to a 1024x1024 image when it's going to show in a 64x64 view
Remove transparency from the images if they are going to display on solid-colored background anyway.
Dont overlay the images with other widgets/controls
If you're still getting a 'slow' UI, maybe try to merge all or multiple images and their surrounding UI/Controls into one or more bigger images
Very long views are not user-friendly. Maybe implement a pager or tab-view etc. to divide your list into multiple views. This way you can also decrease load-time
Dont try to implement an interface in openGL yourself. It's unlikely you'll make a better one than you already get with QtWidgets and QtQuick.
What is the most efficient way of displaying real time plain text?
If I need to display large amount of changing text with high frequency.
What is the best solution?
I have tried QLabel, QPlaintextEdit and I also tried to rewrite a widget's paintEvent and do painting there. But they all do not work very well.
Due to the platform limitation, I cannot use QGLwidget or openGL support.
And the texts need to be grouped in related widgets where the user can perform some basic interaction(like selecting) with those widgets. The expected thing is something like this:
EDIT:
The data comes from many different vehicles' sensors, you could consider that I store the incoming data simply in several arrays. The method I have tried all resulted in a slow responding GUI thread.
I'm drawing some graphics and text with GDI in my CScrollView. I need to implement the zooming functionality. I only need the zoom out functionality, no need to zoom in more than what is normally rendered.
Here are my best ideas:
Use MM_ANISOTROPIC mapping mode with SetWindowExt/SetViewportExt... The problem with this approach is that it does not scale text. Is there any way to force MFC to scale the text as well? Only thing I can think of is to set text font size according to the selected zoom value, but I'm not sure whether this will look well after all...
Draw to memory DC, and use StretchBlt to blit to the client area of appropriate size (set with SetScrollSizes...). This will solve the text scaling issue.
Also it is desirable to have antialiasing effect in the process. I think both methods above should accomplish this per se, but I don't know which will look better. Also I will have to implement printing/print-preview functionality later (using MFC's standard implementation from doc/view architecture), so I need the method to be compatible with that.
Need your advice please. Which way to go and why. Maybe other options exist too?..
You really don't want to mess with the mapping mode when you use MFC -- MFC itself already uses it for (at least) the print preview functionality.
I'd see if SetWorldTransform will work for you. At least with vector/TrueType fonts, it will scale the text along with everything else. Note that before SetWorldTransform will work, you need to call SetGraphicsMode with GM_ADVANCED.
I ended up using the second method I proposed in the question, but used DIBs instead of DDBs (and StretchDIBits() instead of StretchBlt()) because it proved to cause less problems, especially when using big bitmaps, and when printing.
I try to create something, where you can drop different things on it, like the Qt Creator (no, i don't want to create a new one, but i need the function of that).
You drag some elements and drop them anywhere in a tabPane.
My problem now is how to make a grid/raster in the background.
It should look similar to this:
I mean those dots in the background.
If I make them with two for loops, it will take hours and it's not efficient or anything else.
There has to be a more efficient solution and a lot easier one.
I'm programming in c++ with Qt as a Framework. Please give me some links or anything else I can use.
You can:
limit the repainting to region that really needs to be updated as explained in QWidget::paintEvent documentation,
fill a container of QPoint in your loops instead of drawing the points, and draw them all with QPainter::drawPoints after the loop,
cache the result in a QPixmap with transparency and reuse it if the window size didn't change (example from Qt Quaterly).
Of course, you should do some testing to see if you gain anything at all by doing any of these optimizations.
I have an application that I want add some cool animations to show state changes. However, wxwidgets would be difficult because I'd have to program these animations in straight gdi. What's the best way to add these effect windows? Should I open a flash window and run a flash sequence or is maybe some other technology? Does .net have something I could code into a dll and run from my wxwidgets binary? I need something that is super easy to draw and set up the animation.
It's hard to say what the best approach would be to achieve "cool effects", but in most cases you would want a double-buffered drawing surface. That's what I've used in similar-sounding situations.
In wxWidgets, you would want wxBufferedDC.
You could prepare animation as a bunch of images (wxImage loaded from PNG, GIF, JPG or whatever files), and then use a timer and paint them on a control. Maybe it sounds like too much, you I believe you could do it in 50-70 lines of code.
Perhaps you just could make a single widget that has a custom paint-event that hand-draws the various widgets inside it? Then you could draw them at the appropriate locations/sizes without having to involve wxwidgets at all, it would just be a bunch of line-draw/rectangle-draw/text-draw commands to update the display for each frame of animation.