On Thu 20 Nov 2014, Daniel Kurtz wrote:
On Thu, Nov 20, 2014 at 10:34 AM, Chad Versace <[email protected]> wrote:
diff --git a/src/utils/wflinfo.c b/src/utils/wflinfo.c
index 0b03e55..0907b4b 100644
--- a/src/utils/wflinfo.c
+++ b/src/utils/wflinfo.c
@@ -1037,7 +1037,28 @@ main(int argc, char **argv)
if (!glGetString)
error_get_gl_symbol("glGetString");
- glGetStringi = waffle_get_proc_address("glGetStringi");
+ // Retrieving GL functions is tricky. When glGetStringi is supported,
here
+ // are some boggling variations as of 2014-11-19:
+ // - Mali drivers on EGL 1.4 expose glGetStringi statically from
+ // libGLESv2 but not dynamically from eglGetProcAddress. The EGL
1.4 spec
+ // permits this behavior.
In fact, AFAICT, EGL <= 1.4 mandates this behavior, since glGetStringi
is an OpenGL ES 3.0 "non-extension" function.
I think the EGL 1.4 is ambiguous on the topic of OpenGL ES 3.0
functions. Hence the creation of EGL_KHR_get_all_proc_addresses. From
that spec:
With the addition of OpenGL and OpenGL ES 3 support to EGL, the
definition of a non-extension function becomes less clear.
And the EGL 1.4 spec, page 56, 2013-12-04, made a concession to this
ambiguity by adding footnote 21:
eglGetProcAddress may not be queried for core (non-extension) functions
in EGL or client APIs [21].
For functions that are queryable with eglGetProcAddress,
implementations may choose to also export those functions statically
from the object libraries im- plementing those functions. However,
portable clients cannot rely on this behavior.
[...]
[21] In practice, some implementations have chosen to relax this restriction.
So you're right. EGL 1.4 under one interpretation mandates Mali's
behavior. But I believe Mesa is also right under a different
interpretation allowed by the ambiguity.
Anyhow, I think we all agree that what *really* matters is that
everybody's code works, not what some vague phrase in the spec claims.
That is, unless your EGL has EGL_KHR_get_all_proc_addresses [0]:
[0]
https://www.khronos.org/registry/egl/extensions/KHR/EGL_KHR_get_all_proc_addresses.txt
I just sent a patch to mesa-dev to expose this extension, with you CC'd.
+ // - EGL 1.5 requires that eglGetStringi be exposed dynamically
through
+ // eglGetProcAddress. Exposing statically with dlsym is optional.
EGL 1.5 essentially makes EGL_KHR_get_all_proc_addresses part of the standard.
So perhaps the check is something crazy like:
if (extension-function(function) ||
EGL >=1.5 ||
(is_display_init() &&
EGL_has_extension("EGL_KHR_get_all_proc_addresses")) ||
(EGL_supports_client_extensions() && EGL_has_client_
extension("EGL_KHR_client_get_all_proc_addresses")) {
use eglGetProcAddress(function);
} else {
use platform-specific-lookup(function);
}
Do you agree with this?
But you hide the truly crazy part! "use platform-specific-lookup" is
where all the fun code lives, which would contain a fairly large web of
logic.
Rather than correctly implement platform-specific-lookup today, I prefer
the below code, which non-intrusively applies to the maintenance branch:
glGetStringi = dlsym();
if (!glGetStringi) {
glGetStringi = glX/wgl/eglGetProcAddress();
}
I think the above code works for every platform.
But... couldn't we avoid this whole mess by just always using
glGetString() in wflinfo instead of jumping through hoops just to try
to use glGetStringi()?
I wish. glGetString (no i) was removed from OpenGL Core Profile. OpenGL
ES 3.0 kept the function to retain backwards compatibility with OpenGL
ES 2.0.
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