[Bug 730864] New: gl: manage GLSL versions

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=730864
  GStreamer | gst-plugins-bad | git

           Summary: gl: manage GLSL versions
    Classification: Platform
           Product: GStreamer
           Version: git
        OS/Version: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-bad
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: julien.isorce at gmail.com
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


* for deprecated keywords
* for new features

I would like to open the discussion about how to manage the GLSL versions for
deprecated key words, as I have not found an ideal solution after a first
investigation.

attribute and varying keywords are deprecated since GLSL 1.3 (GL3, GLES2 ?).
Not sure in which version they are removed though. in/out should be used
instead.

After initial investigation we could add the following in top of every shader
text:

vs:
"#if __VERSION__ >= 130"
"#define attribute in"
"#define varying out"
"#endif"

fs:
"#if __VERSION__ >= 130"
"#define varying in\n"
"#define out vec4 gl_FragColor\n"
"#endif\n"


If not set by the user, "#version N core" is automatically set with N be the
highest that implementation supports if nothing is specified.

"#version N compatibility" (core is implicit if you do not put it) could be
added to allow using attribute and varying. So maybe "#version __VERSION__
compatibility" could be a solution too. Though I already saw that on my Mac
__VERSION__ is set to 0 whereas it's explicitly mentioned in the 1.2 spec that
it should be defined to the top most supported version.

Or just put "#version 120" in top of our current shaders.

In any cases it seems to also depend of if the driver correctly implement the
spec or not. As mentioned above, __VERSION__ is set to 0 in some cases even on
some mesa versions.

For new features, i.e. in case of one of our shader require a minimal version
to work, we would need to do some probing first to check which version is
available and enable gl elements + some of their feature according to the
actual version. (using GstDeviceMonitor ?)

Any thought ?

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