I want to draw some objects in my Gtk+ application, and let the user interact with them. I know about draw (expose) events and cairo drawing, and have used that before, but now I'm looking for something more like QGraphicsView + QGraphicsScene in QT, or the TK canvas (not HTML canvas!).
The difference is that you don't draw stuff on event, but you tell the widget what objects there are, and it draws them for you. Also it provides z-ordering, and hit-testing for user interaction.
I'm pretty sure such a widget exists for Gtk+, but I can't seem to find it. Can anyone help?
Related
Let's say you have some flutter widget, for example, a TabBar. It is rendered in a rectangular box. I need it to be rendered in an arc so that the text and the underline follow part of a circle (or better still, a bezier curve).
How can that be achieved?
This illustrates what I am trying to achieve - bent TabBar widget:
Please note that in this case, the TabBar bends following and an arc (edge of a circle). This is what I need immediately. However, in the future, I might need bending that follows the edge of an eclipse so a solution that allows it would be preferable.
Also, a solution that works for different widgets is preferred.
IMPORTANT: I do NOT want to clip a curved shape of the widget. The entire area of the widget should stay visible. Instead, I need to bend the content of the widget (=bend its render image).
Apologies for the bold font but without it, people will keep posting answers about how to clip a widget which is trivial in comparison and useless for my problem.
An answer "this is currently not supported by Flutter" from authority (e.g. high reputation in Flutter tag or Flutter a team member) will also be accepted.
One approach: Use a CustomPaint to draw lines/areas/etc freely
You can use a CustomPaint to draw whatever curved lines, areas, etc freely. Therefore, you can definitely achieve your goal - since they are nothing but curved lines, areas with curved edges, rotated texts, etc.
That will take a bit of work, but if you encapsulate it well enough, it is not that hard to implement. For example, draw a Path with filled red area, then draw a white arc, then draw several texts with calculated rotations, etc. Sounds like you can do that within maybe hundreds of lines. If you find difficulty implementing this please comment and I will explain.
Another approach: Hack Canvas such that the call to drawLine becomes indeed calls to drawPath, etc.
You may do the following to allow bend/crook for any widget (and their combination, of course), but this may need a bit of engineering. You can make your own Canvas, say, class BendCanvas implements Canvas {}. The BendCanvas.drawLine, for example, has an implementation of Canvas.drawPath with a curved path cooresponding to the input "line". Similar things hold for drawing rectangles, etc. Then you need to hack Flutter's painting logic, such that it takes in your own BendCanvas instead of the original canvas. This is a universal solution, and it is much more efficient (less code) if you plan to have a lot of bend UI; but if only on bend TabBar, maybe use the first approach.
As for the bend text
In the two approaches above, we have mainly described how you draw the bended rectangle (i.e. draw an arbitrary shaped widget). As for bending text, see: https://github.com/flutter/flutter/issues/16477 , which is still an open issue.
Remarks
It is not possible using transformations. As explained in the comments, you already see Transform does not work - it is affine or perspective, which, by definition, will not bend. Then what about other transforms? After some research there seems to be none. Then, what about looking under the scene. We know Flutter uses Skia under it to draw the UI with high performance, then let us search through Skia. However, it does not provide any transformations like bending. So there seems no use.
P.S. I am not that high reputation in Flutter tag, but I did answer >100 Flutter questions (including some dig-into-source-code style ones), and have developed >100k lines of Flutter code in the production app.
this may look like this question already appeared and in fact it was already touched in this topic Parallel drawing with GTK and Cairo in Python 3 . However is it possible there is another solution to this problem?
To start with, I have created UI in PyGtk with my custom animations executed with the use of threading (Gtk.threads_enter() and Gtk.threads_leave()). It works good and gives out no errors. I also wanted to add some kind of point cloud and I saw that Cairo may be a good fit for it with supposedly support for Gtk.DrawingArea to handle it.
Here is where problem starts. Due to Cairo using drawing event and pretty much overriding it, it draws over my UI the image I made for Gtk.DrawingArea.Image of cairo drawing over UI
So image appears in DrawingArea and is drawn once again over every UI element. I used this tutorial https://blog.fossasia.org/creating-animations-in-gtk-with-pycairo-in-susi-linux-app/ to draw Cairo animation.
Is there a way to somehow make drawing calls from PyGTK to redraw UI elements, so they are not overdrawn by Cairo?
I answered my own question. Draw call needs to be in its own class for DrawingArea as in example https://blog.fossasia.org/creating-animations-in-gtk-with-pycairo-in-susi-linux-app/
I tried to connect it with my own main class but then it was redrawing whole window instead of redrawing only DrawingArea. So when you want to use Cairo, remember to make DrawingArea a custom class.
How to make text scrollable (horizontal and vertical) using Cairo library?
Are there any cairo API which provide scrolling functionality without the use of gtk library?
Cairo only draws things. It has nothing to do with user interaction and thus the whole question does not really make sense, sorry.
Of course you can draw text with cairo at whatever position you want. Thus, to make text scroll you just have to redraw your text based on user input and use a slightly different position each time.
I am working on a game using GTK3 as a rendering technique (terrible idea, but it's a school project).
My gameobjects are made of Image widgets and are placed in a Fixed container. It's working pretty well, however when i move widgets beoynd right or bottom border, the window automatically grows along with it.
I want the window to stay at the sam size, event if widget leaves its area and becomes invisible. It works when i move widget past the upper or left border.
I tried using gtk_widget_set_vexpand and gtk_widget_set_hexpand. My window is set as not resizable (gtk_window_set_resizable).
Is there any way I can achieve this?
This isn't the right way to use GTK+. GTK+ is intended for laying out widgets in a GUI program.
There are better options for animating 2D elements. One that works with GTK+ natively is the Clutter library. You can also integrate SDL or OpenGL or something like that if you so choose.
That being said, you can also use GtkLayout instead of GtkFixed, or put the GtkFixed in a GtkScrolledWindow and hide the scrollbars and set the scroll policy to prevent scrolling. It's still technically misuse, and in fact GtkFixed (and possibly GtkLayout too but the docs don't say) is really not supposed to be used anymore unless absolutely necessary because it doesn't give you automatic support for tricky UI layout problems, but it doesn't have extra dependencies.
I'd like to allow a user to add a shape (which would just be a UIImage) onto some sort of canvas, then move and resize it on the screen but I'm not sure how to go about this. Ideally I'd like the basics of a drawing app which can use images from a user's device. Each shape would have an associated position, size and z-index.
The only thing I'm unsure of is how I'd create a bounding box (the one with four blue dots to allow resizing/moving). I have experience with UIKit, and would prefer to keep the majority of the app in this for the time being, but I get the feeling this type of thing might be better suited to Cocos2D or a similar framework.
If anyone has any pointers/open source code I can dig through it would be hugely appreciated.
I think you should look into CALayer, or even CAShapeLayer. I'm just starting to play with them, but I'm pretty sure you can easily get the functionality you want with either. Draw the border in the layer's drawLayer:inContext:. Check out the Quartz2d Guide path drawing section for the functions you need.