I have a main window which has both a glut UI in the top 10% of the screen, and the openGL world in the bottom 90% of the screen. Every time my cursor starts hovering over the GLUT portion, openGL rendering will freeze. It resumes only when the cursor exits the GLUT area.
This is because as long as the cursor is hovering over the GLUT area, presumably glutIdleFunc is never called because glut is not "idle", so openGL stuff is not rendered.
I already tried making a new unrelated thread that just calls the display code and/or glutPostRedisplay but I got a framerate of whopping 20 fps as opposed to the 100+ fps the normal way. I don't know exactly why. (In this test I also disabled glutIdleFunc so there is no idle func, just the separate thread calling the display)
Ways to get around this (other than "stop using glut" which I might do in the future but for now I would like a temporary solution)?
I know this is an old question, but I was having a similar issue and wanted to share how I solved it.
Basically, in your idle function, you should manually set the window to your normal window ID. Thanks to Joel Davis' HexPlanet code ( https://github.com/joeld42/hexplanet/ ) for demonstrating this:
void glut_Idle( void )
{
// According to the GLUT specification, the current window is
// undefined during an idle callback. So we need to explicitly change
// it if necessary
if ( glutGetWindow() != g_glutMainWin )
{
glutSetWindow(g_glutMainWin);
}
...
}
Create a callback for passive motion func:
void passiveMouseFunc(int,int){
glutPostRedisplay();
}
And register it using:
glutPassiveMotionFunc(passiveMouseFunc);
Related
I have an application which renders a 3d object using OpenGL, allowing the user to rotate and zoom and inspect the object. Currently, this is driven directly by received mouse messages (it's a Windows MFC MDI application). When a mouse movement is received, the viewing matrix is updated, and the scene re-rendered into the back buffer, and then SwapBuffers is called. For a spinning view, I start a 20ms timer and render the scene on the timer, with small updates to the viewing matrix each frame. This is OK, but is not perfectly smooth. It sometimes pauses or skips frames, and is not linked to vsync. I would love to make it smoother and smarter with the rendering.
It's not like a game where it needs to be rendered every frame though. There are long periods where the object is not moved, and does not need to be re-rendered.
I have come across GLFW library and the glfwSwapInterval function. Is this a commonly used solution?
Should I create a separate thread for the render loop, rather than being message/timer driven?
Are there other solutions I should investigate?
Are there any good references for how to structure a suitable render loop? I'm OK with all the rendering code - just looking for a better structure around the rendering code.
So, I consider you are using GLFW for creating / operating your window.
If you don't have to update your window on each frame, suggest using glfwWaitEvents() or glfwWaitEventsTimeout(). The first one tells the system to put this process (not window) on sleep state, until any event happens (mouse press / resize event etc.). The second one is similar, but you can specify a timeout for the sleep state. The function will wait till any event happens OR till specified time runs out.
What's for the glfwSwapInterval(), this is probably not the solution you are looking for. This function sets the amount of frames that videocard has to skip (wait) when glfwSwapBuffers() is called.
If you, for example, use glfwSwapInterval(1) (assuming you have valid OpenGL context), this will sync your context to the framerate of your monitor (aka v-sync, but I'm not sure if it is valid to call it so).
If you use glfwSwapInterval(0), this will basicly unset your syncronisation with monitor, and videocard will swap buffers with glfwSwapBuffers() instanly, without waiting.
If you use glfwSwapInterval(2), this will double up the time that glfwSwapBuffers() waits after (or before?) flushing framebuffer to screen. So, if you have, for instance, 60 fps on your display, using glfwSwapInterval(2) will result in 30 fps in your program (assuming you use glfwSwapBuffers() to flush framebuffer).
The glfwSwapInterval(3) will give you 20 fps, glfwSwapInterval(4) - 15 fps and so on.
As for separate render thread, this is good if you want to divide your "thinking" and rendering processes, but it comes with its own advantages, disadvantages and difficulties. Tip: some window events can't be handled "properly" without having separate thread (See this question).
The usual render loop looks like this (as far as I've learned from learnopengl lessons):
// Setup process before...
while(!window_has_to_close) // <-- Run game loop until window is marked "has to
// close". In GLFW this is done using glfwWindowShouldClose()
// https://www.glfw.org/docs/latest/group__window.html#ga24e02fbfefbb81fc45320989f8140ab5
{
// Prepare for handling input events (e. g. callbacks in GLFW)
prepare();
// Handle events (if there are none, this is just skipped)
glfwPollEvents(); // <-- You can also use glfwWaitEvents()
// "Thinknig step" of your program
tick();
// Clear window framebuffer (better also put this in separate func)
glClearColor(0.f, 0.f, 0.f, 1.f);
glClear(GL_COLOR_BUFFER_BIT);
// Render everything
render();
// Swap buffers (you can also put this in separate function)
glfwSwapBuffers(window); // <-- Flush framebuffer to screen
}
// Exiting operations after...
See this ("Ready your engines" part) for additional info. Wish you luck!
So, I'm creating a game where I have two different windows which have different display functions. What I'm wondering is if it's possible to update two windows simultaneously. Let's say for one window, I implicitly call glutPostRedisplay() to force an update. This will only cause an update on the current window. Yet, I wanted to update both of them.
Is this even possible? I've been searching for quite a long time and didn't seem to some to a definitive answer.
Thanks.
4.5 glutPostRedisplay
glutPostRedisplay marks the current window as needing to be redisplayed.
"Current window" eh? I wonder if...
4.3 glutSetWindow, glutGetWindow
glutSetWindow sets the current window; glutGetWindow returns the identifier of the current window.
foreach( int window : windows )
{
glutSetWindow( window );
glutPostRedisplay();
}
I am trying to rotate a 3d object but it doesnt update when applying transforms in a for loop.
The object jumps to the last position.
How does one update a 3d object's position in a sequence of updates if it wont update in a for loop?
Just calling glTranslate, glRotate or such won't change things on the screen. Why? Because OpenGL is a plain drawing API, not a scene graph. All it knows about are points, lines and triangles that draws to a pixel framebuffer. That's it. You want to change something on the screen, you must redraw it, i.e. clear the picture, and draw it again, with the changes.
BTW: You should not use a dedicated loop to implement animations (neither for, nor while, nor do while). Instead perform animation in the idle handler and issue a redraw event.
I reckon you have a wrong understanding what OpenGL does for you.
I'll try to outline:
- Send vertex data to the GPU (once)
(this does only specify the (standard) shape of the object)
- Create matrices to rotate, translate or transform the object (per update)
- Send the matrices to the shader (per update)
(The shader then calculates the screen position using the original
vertex position and the transformation matrix)
- Tell OpenGL to draw the bound vertices (per update)
Imagine programming with OpenGL like being a web client - only specifying the request (changing the matrix and binding stuff) is not enough, you need to explicitly send the request (send the transformation data and tell OpenGL to draw) to receive the answer (having objects on the screen.)
It is possible to draw an animation from a loop.
for ( ...) {
edit_transformation();
draw();
glFlush(); // maybe glutSwapBuffers() if you use GLUT
usleep(100); // not standard C, bad
}
You draw, you flush/swap to make sure that what you just drew is sent to the screen, and you sleep.
However, it is not recommended to do this in an interactive application. The main reason is that while you are in this loop, nothing else can run. Your application will be unresponsive.
That's why window systems are event-based. Every few miliseconds, the window system pings your app so you can update your state, for example do animation. This is the idle function. When the state of your program changed, you tell the window system that you would like to draw again. It is then up the the window system to call your display function. You do your OpenGL calls when the system tells you to.
If you use GLUT for communicating with the window system, this looks like the code below. Other libraries like GLFW have equivalent functions.
int main() {
... // Create window, set everything up.
glutIdleFunc(update); // Register idle function
glutDisplayFunc(display); // Register display function
glutMainLoop(); // The window system is in charge from here on.
}
void update() {
edit_transformation(); // Update your models
glutPostRedisplay(); // Tell the window system that something changed.
}
void display() {
draw(); // Your OpenGL code here.
glFlush(); // or glutSwapBuffers();
}
I have a scene that is modified when mouse left button is clicked.
My problem is: this modified scene was supposed to appear with a sound, but the scene waits the sounds to finish before it renders itself.
I'm using this function:
do {
alGetSourcei(source, AL_SOURCE_STATE, &state);
} while (state == AL_PLAYING);
Of course, this function tells the program to wait. But what alternative could I use? if I remove this function, the sound isnt played
I even tried to create a function sound(), that is called after glutPostRedisplay but it still waits the sound complete to render
I think your problem, that the sounds stop, is somewhere else. alGetSourcei is not required to keep the sound playing.
Anyway you can't do that in a while loop because it will block the update of the windows messages and OpenGL and will prevent the scene from redrawing.
To play it you just need to call alSourcePlay, after this you could check each frame if the source is still playing ( if you need to do this for some reason ).
I have a strange problem rendering OpenGL to QGLWidget from a different thread than the main thread.
There are a lot of official statements from Qt Developers that it is "perfectly possible" to do rendering from a different thread. I followed the explanation in:
http://doc.qt.nokia.com/qq/qq06-glimpsing.html#writingmultithreadedglapplications
I implemented it nearly the same way. The only difference is, that I dont use QWorkspace with different GLWidgets but instead I just create a MainWindow with GLWidget as central widget.
When I start the application, the rendering thread starts rendering frames with a triangle at a random position. After a while (sometimes 2 seconds, sometimes 10 seconds) the thread starts to block on the swapBuffers() call for a very long time. Sometimes swapBuffers() returns spontanously after several seconds. When I move the mouse pointer over the widget or the main window, the swapBuffers returns immediately and the as long as I move the mouse pointer swapBuffers() does not block. After moving the mouse out of the widget or just stop moving the mouse, rendering continues for some seconds and then swapBuffers start blocking again.
I have absolutely no explanation for this behaviour. I am aware that swapBuffers() regulary blocks until a frame is completed and it's also clear to me, that a wait for vsync also might happen during OpenGL buffer swap call. But that should happen in some milliseconds and not block for several seconds. The environment is X11 with GLX.
Does anybody has an idea wtf is going on here?
I dont even have an idea how to find out what the problem might be..
Does anyone tried to implement the rendering from different thread as explained in the document that I linked above?