Bug 38528 – [Qt] WebGL viewport does not show up on N900

• Status: RESOLVED
• Resolution: FIXED
• Component: WebKit Qt

[Jarkko Sakkinen]

WebGL viewport does not show up anymore on N900 when tested with QtLauncher.

[Jarkko Sakkinen]

Issue here is simple. Higher-level WebGL code does not handle precision arguments yet (I suppose) and WebGL applications do not usually define precisions.

[Jarkko Sakkinen]

Verified that there is no code that handles shader precisions.

[Jarkko Sakkinen]

https://cvs.khronos.org/svn/repos/registry/trunk/public/webgl/doc/spec/WebGL-spec.html#4.4

Issue here is that most of the WebGL pages do not respect that at all :) Shaders are not ES GLSL compatible. They don't define precision arguments.

[Jarkko Sakkinen]

QGLContext::drawTexture functions do not work in Maemo version. Tweaked qgl.cpp a little bit:

diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index 644a737..da61e61 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -2706,7 +2706,7 @@ void QGLContext::drawTexture(const QRectF &target, QMacCompatGLuint textureId, Q
 void QGLContext::drawTexture(const QPointF &point, GLuint textureId, GLenum textureTarget)
 {
     // this would be ok on OpenGL ES 2.0, but currently we don't have a define for that
-#ifdef QT_OPENGL_ES
+#if !defined(QT_OPENGL_ES_2) && defined(QT_OPENGL_ES)
     Q_UNUSED(point);
     Q_UNUSED(textureId);
     Q_UNUSED(textureTarget);


Let's how that helps.

[Jarkko Sakkinen]

Kenneth, Simon says that you have some ideas on handling the precision argument in shader code. Can you elaborate a bit what you have in mind? :)

I think I'll add the following work-around to Qt backend:
- QtWebKit is compiled for a desktop system: define precision arguments as empty macros so that shaders still compile (similar idea as in http://doc.qt.nokia.com/4.6-snapshot/qglshaderprogram.html)
- QtWebKit is compiled for a mobile device: define default precisions and append to the beginning of shader code.

When something more higher-level comes out this workaround can be dropped. Simon, I don't find that too hackish, what do you think?

[Jarkko Sakkinen]

Added new bugreport to Qt Jira: http://bugreports.qt.nokia.com/browse/QTBUG-10420

[Jarkko Sakkinen]

See my comment on Qt Jira. I think point version of drawTexture() is really impossible to make work ES 2.0 but I don't actually can't figure out why rect version is only available for ES versions less than 2.0.

[Jarkko Sakkinen]

Ok that first "patch snippet" was completely crap but now I have patch candidate for rect version, let's see if it works :)

[Kenneth Russell]

(In reply to comment #5)
> Kenneth, Simon says that you have some ideas on handling the precision argument
> in shader code. Can you elaborate a bit what you have in mind? :)

In the context of the ANGLE project ( http://code.google.com/p/angleproject/ ) a GLSL ES -> GLSL translator is being developed. Once this is complete, we hope to work with all browser vendors developing WebGL on the desktop to integrate it simultaneously, because as you've discovered, none of the shaders in the WebGL content currently on the web are GLSL ES compliant.

> I think I'll add the following work-around to Qt backend:
> - QtWebKit is compiled for a desktop system: define precision arguments as
> empty macros so that shaders still compile (similar idea as in
> http://doc.qt.nokia.com/4.6-snapshot/qglshaderprogram.html)
> - QtWebKit is compiled for a mobile device: define default precisions and
> append to the beginning of shader code.
> 
> When something more higher-level comes out this workaround can be dropped.
> Simon, I don't find that too hackish, what do you think?

This sounds like the best short-term workaround.

[Jarkko Sakkinen]

drawTexture() issue is now fixed by Qt people: http://bugreports.qt.nokia.com/browse/QTBUG-10420. Great :) I'm submitting soon patch with workaround for shaders.

[Jesus Sanchez-Palencia]

Please remember to block the 2.0 release meta-bug if you want this to be cherry-picked when the patch is ready.

[Jarkko Sakkinen]

Still waiting for the drawTexture() fix to arrive to Qt public repositories.

[Simon Hausmann]

(In reply to comment #12)
> Still waiting for the drawTexture() fix to arrive to Qt public repositories.

Sounds like we should also make WebGL only available when compiling against Qt 4.7?

[Jarkko Sakkinen]

Depends. If we want to keep readPixels as a fallback for 4.6 then we can support both. I don't really have an opinnion on this, I'll let others to decide this :) 

Simon, have you already created bug for dropping readPixels? We already discussed about readPixels support but does everyone else share the opinnion that WebGL should be only supported with GL viewport? 

drawTexture() can be used for both cases (AC enabled/disabled) when GL viewport is active. I have already fix for this in my gitorious repository and I'm planning to add that change to this patch.

[Jarkko Sakkinen]

Created attachment 56592 [details]
Fixes shader issues with OGLES2, improves drawTexture usage a bit.

[WebKit Commit Bot]

Comment on attachment 56592 [details]
Fixes shader issues with OGLES2, improves drawTexture usage a bit.

Clearing flags on attachment: 56592

Committed r61301: <http://trac.webkit.org/changeset/61301>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.

[Simon Hausmann]

WebGL is not part of the QtWebKit 2.0 release, so removing from the blocker bug.