Why configID = 0 when call eglQueryContext after Unity 2018.3(include)

Unity Engine
,
1

############Code Review##############

eglCurrentContext = eglGetCurrentContext();
if (eglCurrentContext == EGL_NO_CONTEXT)
{
FAIL( “YYYY EGL_NO_CONTEXT”);
}

ret = eglQueryContext(eglDisplay, eglCurrentContext, EGL_CONFIG_ID, &configID);
if (!ret)
{
FAIL( “eglQueryContext EGL_CONFIG_ID failed”);
}

LOG(“eglQueryContext configID : %d”, configID); // configId > 0 before Unity 2018.2, configID = 0 after Unity 2018.3 ???

############Code Review##############

why? I am going to collapse…

2

Did you try using eglGetError - EGL Reference Pages to understand what is happening? :slight_smile:

3

Thanks for your reply.
I have tried to call eglGetError(), but there is no error message.

I checked the egl source code and found that it is allowed to return 0, but I am not clear why it was not 0 before Unity 2018.3。

switch (attribute) {
   case EGL_CONFIG_ID:
      /*
       * From EGL_KHR_no_config_context:
       *
       *    "Querying EGL_CONFIG_ID returns the ID of the EGLConfig with
       *     respect to which the context was created, or zero if created
       *     without respect to an EGLConfig."
       */
      *value = c->Config ? c->Config->ConfigID : 0;
      break;

What was changed in unity 2018.3? why c->Config is null?

4

Then it’s probably due to this: https://www.khronos.org/registry/EGL/extensions/KHR/EGL_KHR_no_config_context.txt

5

Thanks for your reply again.
At present, I use eglQuerySurfece() instead of eglQueryContext() to get the CONFIG_ID。

/*will return correct configID*/
EGLBoolean ret = eglQuerySurface(eglDisplay, eglMainSurface, EGL_CONFIG_ID, &configID);

/*will return configID = 0 */
EGLBoolean ret = eglQueryContext(eglDisplay, eglShareContext, EGL_CONFIG_ID, &configID);

why eglQuerySurface() is OK?:frowning:

6

The extension I linked says:

A context can be used with any EGLSurface that it is
with (subject to the restrictions discussed in the section on
address space). A context and surface are compatible if they were
created with respect to the same EGLDisplay, and if either of the
following sets of conditions apply:

  • The context was created without an EGLConfig. Such contexts match
    any valid EGLSurface.

Which in turn means that:
When a valid surface is created, it has to have a valid config.
When a context is created without a config, if will accept any valid surface.

So it’s totally fine to get the config from the surface.

7

Keep in mind, though, that the surface can be recreated during appliaction runtime.

8

I have the same issue.

I want to know why Unity 2018.3.X can’t get configID through eglQueryContext but Unity 2018.2.X could.

ret = eglQueryContext(eglDisplay, eglCurrentContext, EGL_CONFIG_ID, &configID);

Is there a bug in Unity 2018.3.X ?

9

As I mentioned earlier, I suppose this is because we started using the EGL_KHR_no_config_context (https://www.khronos.org/registry/EGL/extensions/KHR/EGL_KHR_no_config_context.txt) extension.