I'm trying to fiddle a bit with a Qt example regarding 2D Graphics.
Basically it is a small diagram editor. In the example, the author explains that the tracknodes() function is used to update the line's endpoints, when the user drags a connected node into a different position.
This actually does not happen. After looking at the code, I have the feeling it's because there is no event being called after moving the node QGraphicItem, in order to update the link's rendering.
I figured I have to find out where and how the QGraphicItem's movement is handled in order to send a wasDropped signal (or something like that) to a slot that re-renders the link. Does this make sense?
I'm pretty new to Qt/C++ in general, so I don't have a very clear idea on how to achieve this, does anyone have any pointers he/she could share?
He seems to be using the QGraphicsItem::itemChange virtual function to call the tracknodes() function which draws the lines. ItemChange should be called every time a node is moved. It's called in other cases as well but he only uses it for tracking the movement of the QGraphicsItem.
Related
I am creating a game in GMS2. I am using "show_message_async()" in my code. I know that when it is run, a message pops up on the screen and the game still runs in the background. However, I want the game to freeze in the background while the message pops up. Is it possible to do this? And if so how.
You should try looking up instance_deactivate_all(notme) and instance_activatie_all(notme)
https://docs.yoyogames.com/source/dadiospice/002_reference/objects%20and%20instances/instances/deactivating%20instances/index.html
This will disable all objects in a room except the object that's calling it (which should be the menu object that shows the message)
The only tricky part of it, it that it also disables drawing the objects. resulting in an empty screen. For this, you could either use a black screen, or draw a screenshot of the scene before they're disabled.
I agree with Steven's answer. To add on his answer about taking the screenshot of the game, you probably need to make a new surface, then use surface_copy from application_surface before deactivating the object.
How would I use Processing to make visually-appealing buttons that when clicked will send data through a serial port? Is this possible in Processing or would I need to use something else?
You're really talking about two different things:
How do I draw a button?
How you do this depends entirely on you. You could just draw a rectangle using the rect() function or a circle using the ellipse() function, then put some text in there with the text() function. Or you could load an image file and draw that using the image() function. It's entirely up to you.
How do I do something when the user clicks a button?
This is a little trickier, but still pretty easy in Processing. You would use the mouseX and mouseY variables and if statements to check whether that position is inside one of your buttons, and then do the correct thing if so.
Processing comes with several examples of buttons, you should take a look at those.
Another option is to use a GUI library, but that's probably overkill if you just want to show a couple buttons.
Using Cocos3D, is it possible to take screenshot of the 3D model in the background without the user knowing it?
For pre-processing purpose and other usage, I want to take screenshots of the 3D model at various angles. Following the Render-To-Texture capability, I noticed when my scene is not visible, the drawSceneContentWithVisitor: method only execute once rather than at every rendering cycle. For obvious reason, the CC3GLFramebuffer* won't get updated with new data, hence, I'm only able to take the initial screenshot.
Thanks.
In Cocos3D, you can render your 3D scene to an off-screen surface. See the CC3DemoMashUp addTelevision and drawSceneContentWithVisitor: methods for an example of how to do this.
What is important is that the 3D drawing environment has been established when you perform your drawing. The safest place to do this is inside your drawSceneContentWithVisitor: method. But if you want to render somewhere else, you need to invoke the CC3Scene open3DWithVisitor: and CC3Scene close3DWithVisitor: methods before and after rendering. See the implementations of the CC3Scene processInitializeScene and open methods for examples of how to do that.
To render your scene from multiple viewpoints, you need to add multiple cameras to your scene, and set the camera property of your drawing visitor appropriately to select a camera before rendering. See how this is done in the CC3DemoMashUpScene addTelevision and drawToTVScreen methods. The drawToTVScreen method also shows how to handle clearing the color and depth buffers of your surface.
Looking through the documentation, it seems that the new advanced gestures API doesn't determine the direction of a swipe beyond the basic { left, right, up, down }.
I need the start point of the swipe and the direction.
Is there anyway to retrieve this other than coding my own advanced gesture library from scratch out the basic gestures?
And if this is my only option, could anyone point me to some open source code that does this?
Got it! Documentation is here, under 'Creating Custom Gesture Recognizers' at the bottom.
Basically the six gestures Apple provides all derive from UIGestureRecognizer, and you can make your own gesture recogniser in the same way.
then, inside your view's init, you hook up your recogniser. and just the act of hooking it up automatically reroutes incoming touch events.
Actually, the default behaviour is to make your recogniser an Observer of these events. Which means your view gets them as it used to, and in addition if your recogniser spots a gesture it will trigger your myCustomEventHandler method inside your view (you passed its selector when you hooked up your recogniser).
But sometimes you want to prevent the original touch events from reaching the view, and you can fiddle around in your recogniser to do that. so it's a bit misleading to think of it as an ' observer '.
There is one other scenario, where one gesture needs to eat another. Like you can't just send back a single click if your view is also primed to receive double clicks. You have to wait for the double-click recogniser to report failure. and if it is successful, you need to fail the single click -- obviously you don't want to send both back!
I am naive to Qt and GUI programming.
Qt jpg image display
The procedure given for displaying an image is working fine and thank you for providing that. But I want to display an image when I click on radiobutton.
I created a slot, and I connected the button click event to the slot (dispImage is my slot). My slot consists only the code which is working to display an image (First answer in this link).
I am able to compile it and run it. But the o/p is not as we desire.
On button click, image window flashes for a sec and disappears.
One more point to share is, I tried the same with windowsflags example present in qt examples.
In this example I want to display the image on the preview window created by us. Even this is also not worked for me.
Please provide me the solution.
Thanks in advance.
This is happening because the method that you're connecting to the slot is creating all of the objects needed to display the image on the stack and they're going out of scope and being destroyed when that method returns. The linked example has the event loop running at the end of the method, so the objects don't go out of scope until the program exits.
You can fix this by making the necessary objects member variables of a class that has application lifetime.
Stu's answer above is correct.
If you don't understand what he's talking about, you may want to get a little bit more familiar with C++ before jumping into Qt. The example you are citing is different from what you are trying to do. It's a main() function whose stack variables aren't going to go out of scope until the process exits (that's when main() returns). The stack variables in a method go out of scope as soon as the method returns.
Using the example you cite as a template for your method, you need to declare the QGraphicsView object as a class variable in the header file for your radioslot object. This will make it so it stays in scope until your radioslot object is destroyed.