[Interest] OpenGL ES 3.1 and Tessellation

[Daniel Watkins]

Thanks Laszlo,

The conflict with including <GLES3/gl31.h> ended up being an issue with
including other Qt headers at the same time. I was able to resolve all
needed functions with getProcAddress and got ES 3.1 working fine.
QOopenglES2ext.h had everything else I was worried about such as
GL_PATCHES_EXT too.

On Sun, May 17, 2015 at 12:47 PM, Agocs Laszlo <
laszlo.agocs at theqtcompany.com> wrote:

>
>  Hi,
>
>  When targeting Android, setVersion(3,1) is enough (and may not even be
> required with most drivers since they will give you the highest ES version
> anyhow). Setting the renderable type is not necessary since the default on
> that platform is ES. Setting the profile is wrong, that concept does not
> exist in ES.
>
>  You can then simply include <GLES3/gl31.h> and use the functions
> directly. (this should work, the conflicts you mentioned are not expected)
> For extensions, use
> http://doc.qt.io/qt-5/qopenglcontext.html#getProcAddress and extension()
> / hasExtension(). qopengles2ext.h provides the constants and function
> pointer typedefs for pretty much all extensions, but you have to do the
> function resolving manually.
>
>  If you are after something more cross-platform, for example developing
> your app with GLES 3.1 features on a desktop platform using OpenGL 3/4,
> then it becomes trickier. QOpenGLFunctions (the non-versioned one) provides
> a cross-platform, cross-GL-GLES wrapper for all of GLES 2.0, but it does
> not contain any ES 3.x functions at the moment. Therefore the way to go for
> now is to use QOpenGLFunctions for ES 2.0 functions and call the ES 3.x
> specific ones directly (when running on an OpenGL ES platform) or via the
> versioned QOpenGLFunctions_N_M wrappers (when on OpenGL).
>
>  The versioned wrappers are fairly useless when it comes to ES:
> QOpenGLFunctions_ES2 has no proper cross-GL-GLES compatibility and is
> available only in -opengl es2 builds, i.e. when the functions are callable
> directly anyhow. Adding an ES3 or ES31 variant would not really solve the
> problems here.
>
>  Extending QOpenGLFunctions with ES 3.0/3.1 is on the table, but no
> concrete plans are available yet. Maybe Qt 5.6, maybe 5.7.
>
>  Best regards,
> Laszlo
>
>
>   From: Daniel Watkins <dwatkins at valpineware.com>
> Date: Sunday 17 May 2015 06:04
> To: "interest at qt-project.org" <interest at qt-project.org>
> Subject: [Interest] OpenGL ES 3.1 and Tessellation
>
>   Hey guys,
>
>  I've been scavenging the internet for a few weeks here trying to figure
> out how to access OpenGL ES 3.1 through Qt. According to the new features
> list for the 5.4 and 5.5 releases, there is talk about ES 3, but there
> doesn't appear to be much documentation about how to use it. It seems that
> to get an ES 3.1 context for a QQuickView, you can do the following:
>
>  QSurfaceFormat format = view.format();
>
> format.setProfile(QSurfaceFormat::CoreProfile);
>
> format.setRenderableType(QSurfaceFormat ::OpenGLES);
>
> format.setVersion(3, 1);
>
> view.setFormat(format);
>
>
> But is there a way to actually access the ES31 functions? There clearly is not a QOpenGLFunctions_ES31 class. I tried straight up including the Khronos header file, but that ended up with some conflicts. Rummaging around in the qtbase/src/gui/opengl directory, there appears to be a private QOpenGLES3Helper class, and talk about the Android extensions pack, which leads to my next concern.
>
>
> How might someone go about accessing the tessellation shader extensions available on certain Android devices? I'm seeing this #define GL_ANDROID_extension_pack_es31a in qopengles2ext.h, so it appears likely possible.
>
>
> Thanks in advance
>
>
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