# Problem with double-buffering and Nvidia on Linux / wayland

**URL:** <https://discourse.glfw.org/t/problem-with-double-buffering-and-nvidia-on-linux-wayland/2170>\
**Category:** support\
**Created:** [October 9, 2022, 10:31am UTC](https://discourse.glfw.org/t/problem-with-double-buffering-and-nvidia-on-linux-wayland/2170 "2022-10-09T10:31:09Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![mulle-kybernetik-tv](https://yyz1.discourse-cdn.com/flex035/user_avatar/discourse.glfw.org/mulle-kybernetik-tv/32/678_2.png) [@mulle-kybernetik-tv](https://discourse.glfw.org/u/mulle-kybernetik-tv)\
**Post date:** [October 9, 2022, 10:31am UTC](https://discourse.glfw.org/t/problem-with-double-buffering-and-nvidia-on-linux-wayland/2170/1 "2022-10-09T10:31:09Z")

</div>

First up, I don’t think this is really a problem of glfw, but I am looking for some ideas. For example: is this only happening on my machine ?

I wrote a very simple program that makes one of the framebuffers “orange” and the other “blue”. Then the “orange” and “blue” are swapped every 0.5s. This works as expected on my notebook with Intel graphics, but not on my desktop with Nvidia:

```c
int main( int argc, char *argv[])
{
    if (!glfwInit())
        exit(EXIT_FAILURE);

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);

    GLFWwindow* window = glfwCreateWindow(640, 480, "Demo", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        exit(EXIT_FAILURE);
    }

    glfwMakeContextCurrent(window);
    glfwSwapInterval(0);

    glClearColor( 0.7, 0.3, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);
    glfwSwapBuffers(window);

    glClearColor( 0.0, 0.3, 0.7, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);
    glfwSwapBuffers(window);

    glfwSwapInterval(30);

    while (!glfwWindowShouldClose(window))
    {
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glfwDestroyWindow(window);

    glfwTerminate();
    exit( EXIT_SUCCESS);
}

```

On Nvidia I just see the “blue” buffer. That’s with the all the drivers I have available: nouveau and the 470/515 proprietary drivers.

I am running: `Ubuntu 22.04.01 LTS / Wayland / nouveau / Nvidia 3060 Ti`

---

<div class="post-metadata">

**Author:** ![dougbinks](https://yyz1.discourse-cdn.com/flex035/user_avatar/discourse.glfw.org/dougbinks/32/39_2.png) [@dougbinks](https://discourse.glfw.org/u/dougbinks)\
**Post date:** [October 9, 2022, 11:07am UTC](https://discourse.glfw.org/t/problem-with-double-buffering-and-nvidia-on-linux-wayland/2170/2 "2022-10-09T11:07:46Z")

</div>

Welcome to the GLFW forum!

GFLW on Wayland uses [EGL by default for context creation](https://github.com/glfw/glfw/blob/master/src/wl_window.c#L1806-L1823), and thus the `glfwSwapBuffers` calls [eglSwapBuffers](https://registry.khronos.org/EGL/sdk/docs/man/html/eglSwapBuffers.xhtml).

From the documentation `EGL_SWAP_BEHAVIOR` attribute would need to be set to `EGL_BUFFER_PRESERVED` to preserve the back buffer, and this is not set by GLFW. The behaviour of buffer swapping is not consistent across APIs/OSs/Drivers so I do not think it would be useful for GLFW to set this, but you could use [the native interface](https://www.glfw.org/docs/3.3/group__native.html) to get the EGL surface and set the surface attribute yourself.

Generally OpenGL programs which wish to preserve rendered pixel data do so through render to texture.

---

<div class="post-metadata">

**Author:** ![mulle-kybernetik-tv](https://yyz1.discourse-cdn.com/flex035/user_avatar/discourse.glfw.org/mulle-kybernetik-tv/32/678_2.png) [@mulle-kybernetik-tv](https://discourse.glfw.org/u/mulle-kybernetik-tv)\
**Post date:** [October 9, 2022, 12:50pm UTC](https://discourse.glfw.org/t/problem-with-double-buffering-and-nvidia-on-linux-wayland/2170/3 "2022-10-09T12:50:48Z")

</div>

Thanks, the information about `EGL_SWAP_BEHAVIOR` is very interesting, as I didn’t know that. Yet that can’t really be the problem here, as a swap should then reveal the destroyed framebuffer contents as some random garbage or black. Instead it’s just “blue” as if doesn’t really swap. I modified the example to use a single buffer and this just shows black, which is even worse 🙂 :

```c
int main(void)
{
   struct timespec delay = { 0, 500 * 1000L * 1000L};

   if (!glfwInit())
     exit(EXIT_FAILURE);

   glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
   glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
   glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
   glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
   glfwWindowHint(GLFW_DOUBLEBUFFER, GLFW_FALSE);

   GLFWwindow* window = glfwCreateWindow(640, 480, "Demo", NULL, NULL);
   if (!window)
   {
      glfwTerminate();
      exit(EXIT_FAILURE);
   }

   glfwMakeContextCurrent(window);

   for(;;)
   {
      glfwPollEvents();
      if( glfwWindowShouldClose(window))
         break;

      glClearColor( 0.7, 0.3, 0.0, 0.0);
      glClear(GL_COLOR_BUFFER_BIT);
      glFlush();
      nanosleep( &delay, NULL);

      glfwPollEvents();
      if( glfwWindowShouldClose(window))
         break;

      glClearColor( 0.0, 0.3, 0.7, 0.0);
      glClear(GL_COLOR_BUFFER_BIT);
      glFlush();
      nanosleep( &delay, NULL);
   }

   glfwDestroyWindow(window);

   glfwTerminate();
   exit( EXIT_SUCCESS);
}

```

---

<div class="post-metadata">

**Author:** ![mulle-kybernetik-tv](https://yyz1.discourse-cdn.com/flex035/user_avatar/discourse.glfw.org/mulle-kybernetik-tv/32/678_2.png) [@mulle-kybernetik-tv](https://discourse.glfw.org/u/mulle-kybernetik-tv)\
**Post date:** [October 9, 2022, 2:52pm UTC](https://discourse.glfw.org/t/problem-with-double-buffering-and-nvidia-on-linux-wayland/2170/4 "2022-10-09T14:52:35Z")

</div>

One thing I found out is, that I actually didn’t compile with `GLFW_USE_WAYLAND` anymore, due to a recently introduced misconfiguration in my build setup ☹. So the code is actually using X11.

Now with glfw compiled for Wayland, the window contents are complete trash, which is probably what one would expect. So now I tried `eglSurfaceAttrib( display, surface, EGL_SWAP_BEHAVIOR, EGL_BUFFER_PRESERVED);` but it returns `GL_FALSE`.

The EGL dox say:

```nohighlight
EGL_BAD_MATCH is generated if attribute is EGL_SWAP_BEHAVIOR, value 
is EGL_BUFFER_PRESERVED, and the EGL_SURFACE_TYPE attribute 
of the EGLConfig used to create surface does not contain 
EGL_SWAP_BEHAVIOR_PRESERVED_BIT.

```

I tried patching this into `src/egl_context.c` but this yields `error: 'EGL_SWAP_BEHAVIOR_PRESERVED_BIT' undeclared`.

The single buffer test code, now fails, as no window is being created, which is probably what one would expect in this situation, if framebuffer content preservation is not set.

Oh well…

---

<div class="post-metadata">

**Author:** ![dougbinks](https://yyz1.discourse-cdn.com/flex035/user_avatar/discourse.glfw.org/dougbinks/32/39_2.png) [@dougbinks](https://discourse.glfw.org/u/dougbinks)\
**Post date:** [October 9, 2022, 3:34pm UTC](https://discourse.glfw.org/t/problem-with-double-buffering-and-nvidia-on-linux-wayland/2170/5 "2022-10-09T15:34:37Z")

</div>

> [@mulle-kybernetik-tv](#):
>
> I tried patching this into `src/egl_context.c` but this yields `error: 'EGL_SWAP_BEHAVIOR_PRESERVED_BIT' undeclared`.

I’m guessing you mean it fails to compile because `EGL_SWAP_BEHAVIOR_PRESERVED_BIT` is undeclared? This is because GLFW places required defines in the `internal.h` header, you need to look up the value of the defines you need and add them to this (this is done to simplify building GLFW).

> [@mulle-kybernetik-tv](#):
>
> Yet that can’t really be the problem here, as a swap should then reveal the destroyed framebuffer contents as some random garbage or black. Instead it’s just “blue” as if doesn’t really swap.

The behaviour of EGL without `EGL_BUFFER_PRESERVED` set and the behaviour of GLX are that _The contents of the color buffer are undefined_. The swap behaviour of some drivers/hardware is to copy the contents, so the results you see on GLX could be due to this. Generally it is not safe to assume undefined behaviour will do a specific thing.

I would again recommend looking into render to texture (using OpenGL framebuffers) if you want to preserve your rendered pixel content for future use, especially as you are using OpenGL 3.3 which fully supports this.

---

<div class="post-metadata">

**Author:** ![mulle-kybernetik-tv](https://yyz1.discourse-cdn.com/flex035/user_avatar/discourse.glfw.org/mulle-kybernetik-tv/32/678_2.png) [@mulle-kybernetik-tv](https://discourse.glfw.org/u/mulle-kybernetik-tv)\
**Post date:** [October 9, 2022, 4:13pm UTC](https://discourse.glfw.org/t/problem-with-double-buffering-and-nvidia-on-linux-wayland/2170/6 "2022-10-09T16:13:21Z")

</div>

Rendering into textures is no problem per se. But I thought I could make this easier for me, by reusing framebuffer contents. Which I can’t now, unfortunately. Thanks for the help.