I'm writing a video annotation application with Qt4 in which users need to be able to seek to various points in a video, putting markers on various objects and then setting keypoints for those markers so that they stay on the objects in the video as they move around. QGraphicsItemAnimation seems like a great place to start for these markers, however they need to be able to appear and disappear at specific times, which I can't figure out how to do with the QGraphicsItemAnimation. I could set the scale at 0 to make the objects disappear, but that seems like a pretty hacky solution, and I'm guessing that the paint engine would still waste cpu cycles trying to draw those invisible objects. Does anyone have a better solution than this? I'm using Qt 4.5.3 right now, but I'm willing to upgrade to 4.6 if it makes things easier. Thanks!!
It seems like the functionality you want of showing/hiding QGraphicsItem objects is beyond the scope of the simple "tweening" that the animation class performs. It is only for one object at a time, and any appearance or disappearance you have to write yourself.
You still might get some mileage out of QGraphicsItemAnimation (although the fact that it uses its own timer instead of being locked to the frame clock of your video is a little dodgy).
Neglecting "seeking" for a moment, there is a QTimeLine::finished() signal. If you let the end of an annotation's active animation timeline represent the point where you want it to disappear, you can trigger QGraphicsItem::hide() at that point. When it comes time to turn it back on, you would construct a new QGraphicsItemAnimation (based on the next run of keyframe data for that object) and call QGraphicsItem::show().
Note that one of the headlining features of Qt 4.6 is the QtAnimation framework, which is more sophisticated but also rather complex. I've not used it yet, but looking over the examples it seems like you might be able to "animate" a visibility or opacity property.
Related
wisgetwas wondering what widget in gtk (using gtkmm) could be used to implemented the movable button looking thing in the picture. and also the dotted line.
dotted line
edit: the widget is supposed to be able to move left and right along the time-track to be able to set the play bounds. Here is a video showing how it looks like in after effects. From sescond 37 is how the behaviour for it supposed to be. https://www.youtube.com/watch?v=QxXevteeumg
edit: from what it looks like there isnt a specific widget which could simplify this. However a regular button can be used and then implementing a method for its drage using the various signal handlers associated with a Gtk button
There is no widget that does this (see the widget gallery).
You can, however, add custom widgets using Cairo. In the official Gtkmm book, there is an example for creating a custom clock widget using the Gtk::DrawingArea. The Gtk::DrawingArea offers a lot of signals which you can connect to.
I have created my own widgets in the past using this and it worked just fine. However, it was a lot of work because:
Cairo lacks good documentation. Understanding the philosophy behind this library is a lot of work, often empirical.
It can be hard to acheive acceptable performance using Cairo. One has to be really careful in how the drawing of the widget is performed. There is often a naive way to do it, which is clearer in the code, but devastating in terms of performance (it often involves useless redraws on the CPU).
I've been trying to figure out the best way to show an existing CALayer in a secondary window to allow real-time full-screen output on a secondary monitor. Additionally I would like to have the ability to show real-time thumbnails in my application of the original CALayer, it seems like I should be able to find a setup that could fulfill both requirements.
So far my research resulted in the following options:
CALayer.render(in: CGContext) Using the original layer and redrawing it to additional views this way and setting up a timer or a CVDisplayLink to redraw it every frame.
Rendering the CALayer to a NSBitmap every frame. And using that bitmap in NSImageView across the application.
Using a CAMetalLayer and rendering the texture multiple times using a MTKView. I'm not really familiar with Metal, this seems like a fairly elegant solution, but I'm not sure if it is required to go all the way down to Metal myself.
Using a CARemoteLayerServer with a CARemoteLayerServer.
This seems like an overly complicated setup for in-process sharing of a CALayer and it feels like this approach is more suitable if I'd need to share the layer cross-process.
Using CAReplicatorLayer. Instead of using the replicator layer to create a grid of copies I tried to use it to create just one copy, but it seems like you cant add a CALayer to multiple "parent layers".
All in all I've found some workable solutions, but as I'm quite a novice working with Core Animation I'm not sure which direction is the least resource-heavy and I might still be missing an easier solution.
Has anyone tried something similar?
I am making a drawing on NSView using a timer that is set to update every .02 seconds. On update some physical simulation makes a step, and then Canvas!.needsDisplay = true. It works when app is in foreground (usually), but when some lags happen, simulation progresses forward despite the fact that view hasn't reflected it yet. How do I pause the timer during these times to make simulation happen only when NSView can show it? I do not want to call step_over from inside drawRect, cause it seems like a bad idea, because then it would be harder to stop the simulation.
Generally this kind of update should be done the other way around, by letting the display ask you for frames as it can display them. This is done with a CADisplayLink CVDisplayLink (this is Mac; CADisplayLink is iOS). Configure it with a method you want to be called when a frame can be drawn.
Generally you do want your simulation to keep moving forward, even if it means dropping frames occasionally. For that, you check the timestamp and use that to work out what time to use for your new frame. But if you only want to move forward when the display can show it, then just update once per call.
Note that generating at 50fps is often going to mismatch the system that's trying to draw at 60fps, so you're going to wind up missing frames occasionally. That's one of several reasons not to try to push drawing with a timer.
See also Alternative of CADisplayLink for Mac OS X. Note that trying to draw at 50fps with Core Graphics usually isn't going to give good results in any case. The right tool here in OS X is Core Animation (or SpriteKit for games on 10.10, or OpenGL for more advanced high-speed rendering). You can do very basic animations with an NSTimer (and we did for years before Core Animation came along), but it's not really a tool for complex drawing.
Nearly every example I see of OpenGL ES involves it updating every frame, even if the image itself is not moving in any way.
I did some tests and I see it works quite fine to just render (using drawArrays etc) and then present the render buffer (these two actions, together) just once and then not do either again until you have something change onscreen.
Is this "normal" ? I just don't see this really done much. Once drawn, the graphics stay on the screen without additional constant rendering.
Is this acceptable?
Yes, it is acceptable and completely valid. You also need to take account to render again when the context is lost. To give you an example, using Android standard OpenGL helper classes there is an option to only draw when needed, not in loop (RENDERMODE_WHEN_DIRTY).
I'm developing my first Android game and I'm having a bit of difficulty making the UI as smooth as I would like. I've spent a couple of hours googling around with no luck, I'm probably just searching for the wrong thing.
I have two different XML layout resources where each layout contains just one SurfaceView subclass. When I call activity.setContentView(R.layout.second_layout) to transition from the first layout to the second layout there is a noticeable period of time where a black screen (with a small white bar along the top) is displayed in between the two views.
I've tried various things such as; constructing the second view manually at runtime (i.e not using a layout XML file), calling activity.overridePendingTransition(android.R.anim.fade_in, android.R.anim.fade_out) after activity.setContentView(R.layout.second_layout) and attempting to render to the canvas before the view has loaded (turns out the canvas is unavailable).
I don't see other games (or apps) having this issue so I presume there is a reasonably simple solution.
If you need some more information about my particular situation in order to help out then please let me know what information is missing. Any help would be largely appreciated.
Update: My answer below was written in 2010. Since then Fragments have become the norm, particularly since Fragment nesting was made possible and the support library allows this functionality to be used in a backwards compatible fashion. As such, instead of transitioning to a new Activity to perform a new "user task", you can use the one Activity and push and pop fragments within that Activity's view hierarchy. Animations can also be performed as a part of a fragment transaction (e.g. Fragment transaction animation: slide in and slide out).
This became pretty apparent not long after posting this question, however I thought I should come back here and make it clear to everyone else.
Activities are positively the way to go when developing for Android. Don't be put off by the fact that a transition may seem too minor for a separate Activity, the very foundation of Android is built around the idea of an Activity.