I've got a C++/QWidgets application with 2 Qt3DWindow embedded. The 3D windows can be hidden (i.e. the user switches to another view), while work is done in other parts of the application. Whenever the user switches back to the view with the embedded Qt3DWindow there are a lot of changes to be made to the scenegraph.
Rendering is set to OnDemand, but whenever the view is switched back to the 3D windows there is a big lag, up to several seconds. Profiling the application has shown that a lot of work is done for rendering at that point because the scenegraph is changing (most time is spent in the material classes).
My working theory is, that each change to the scenegraph (i.e. removing an entity, adding a new one) causes a separate render update, which leads to the lag due to the amount of separate changes.
So my question is:
Is there a way to stop all render updates until the scenegraph has been updated/modified completely?
I'm thinking of something similar to the beginResetModel() and endResetModel() methods in QAbstractItemModel.
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My app uses modern OpenGL and MFC. I have a very large model, which means rendering is heavy and slow. I want to avoid frequent redraw of the large model as much as possible.
I know OpenGL always redraws everything to show updates. What I am looking for is sth like below:
The large model will be rendered once and then stays as background.
On top of the model, users can drag&draw line works. During the drag&draw process, the OpenGL will constantly update/redraw the line works(but not the model).
When users are done with line works, the large model will update once to include the lineworks.
The problem is that how do I make OpenGL only redraw the line works but keep the model as background during the drag&draw?
As I understand rendering textures in SDL2, everything is waiting behind the scenes and a texture appears after using the SDL_RenderPresent() function and vanishes with SDL_RenderClear(), which you use before advancing to the next frame.
I understand that as far as it goes for imagery, but what about functionality? I have two button textures linked to mouse events that I want to see and use at different times in different places. I've got them rendering during different enum states and each button does indeed appear and disappear on cue when the states change.
However, since both button textures are always "there" even while not being rendered, I can still mouse click on the invisible button that isn't being rendered at any given time. This doesn't seem to be an issue for mouse motion events, just mouse button events. How do I make a texture inactive as well as invisible when it's not being rendered?
I solved this one with some tinkering and a more experienced programmer named mbozzi's help to clue me in the right direction as to what was going on. The underlying issue was due to my completely decoupling the GUI logic and GUI rendering. Which is what we are always told to do: decouple everything, right? But I needed to couple the logic and rendering that I want to occur at the same time and place.
My event poll>>mouse input>>image rendering code was one giant loop. However, when I split that giant loop into separate mini event poll>>mouse input>>image rendering loops that each runs independently (but not concurrently, I just put them in their own different enum game states), that clears up the issue. So, if anyone has a similar problem with clicking invisible buttons, hopefully this will help.
I'm working on an OpenGL project where there are many scenes. I have successfully implemented the functionality of switching scenes at runtime, so the user can change to another scene by choosing a scene name through the ImGui menu. When that happens, the current scene is deleted to clean up dirty OpenGL internal states, then the new scene will be loaded from a factory pattern. Everything works fine, except that the window will freeze for a few seconds during the transition because unloading/loading scenes takes quite a while to finish.
What I want to do now is to create a loading screen, which will be displayed in between. The task of unloading/loading scenes is scheduled asynchronously using std::async and std::future, so that the caller is non-blocking and my loading screen can show up. However, since I'm creating the new scene in background in another thread, that thread cannot see the OpenGL context in the main thread, as a result, any glxxxx() calls would cause access violation so the new scene cannot be created.
I know that OpenGL is a global state machine which does not support multithreading quite well. I've also read somewhere that it is driver-dependent. Most threads on this topic is old, I wonder if it is still difficult to use multithreading in OpenGL as of 2021. From what I see, loading screen and switching scenes are just very basic functionalities, many applications are able to do so, and I believe there're a bunch of them using OpenGL, why is this problem still not commonly addressed today?
Does anyone know of any external libraries in this regard? Or is there another workaround without using multiple threads?
I am planning on making a 3D scene editor app using c++ and open gl. And I have to keep track of the current loaded project and different scenes it contains also the user preferences and other things. The best solution I can think of is to wrap them in a context class which will be a singleton. Is there a better way of doing this?
Not a good idea, probably. One reason is technical. The actual OpenGL context's lifetime is limited and is far shorter than app itself, usually related to surface you're outputting to. You would need to initialize context after your visualizing window is ready and de-initialize it before window is gone. Trying to do so when window gone may end to undefined behaviour depending on platform. In some cases you might need several contexts.
Another reason is, it doesn't look like proper separation of responsibilities. User settings aren't part of context, but some may affect only a single render pass (out of plural). You likely would have Preferences, Renderer which would be an interface to Context manager, Geometries, Textures (or materials) separate, an Scene Manager as well (think of scene tree in Blender or DAZ studio, each item in scene can have separate user settings, regarding how to visualize them).
I've been developing a 2d RPG based on the LWJGL alongside with Java 1.6 for 3 months now. My next goal is to write all of the non-game-ish stuff. This includes menus, text input boxes, buttons and things like the inventory and character information screens. As I am a Computer Engineering student, I'm trying to write everything on my own (except, of course, for the OpenGL part of the LWJGL) so that I "test" myself on the writing of a simple 2d game engine.
I know that making such things from scratch requires basically mapping textures to quads (like the buttons), writing stuff on them and testing mouse/keyboard events which trigger other events inside the code.
The doubt I have is: should I use VBO's (as I'm using for the actual game rendering) or Immediate Mode when rendering such elements? I don't really know if Immediate Mode would be such a drop on performance. Another point is: do the interface elements have to be updated as fast as the game itself? I don't think so, because nothing is actually moving... Are actual games made like that?
Immediate Mode is more straightforward for the task, you would not need to take care about caching and controls composition/batching. Performance dropoff is not that big, unless you render a lot of text (thousands of letters) with each glyph in a separate glBegin..glEnd. If you don't use VBO anywhere else I would recommend trying it out for text output and doing everything else in easier Immediate Mode.
GUI elements might not change as often as game state does, but there's a catch - you could need to update them each time there's a cursor interaction (e.g. button gets OnMouseOver event and needs to be rendered with a highlight). These kind of events may happen very frequently, so thats why rendering may be needed at a full speed.