This is a fragile bit, very device specific, and hard to maintain. Let's take some burden off gfx team :)

Okay, digging into this I could see that on Gonk we have Hwc also handling VSync. Should we also kill this ?

Review commit: https://reviewboard.mozilla.org/r/68896/diff/#index_header See other reviews: https://reviewboard.mozilla.org/r/68896/

Ok, this patch builds but effectively kills any gfx rendering after the boot animation. I have no idea why :)

On recent android, hwc always exist as final stage of composition. We can not remove HwcComposer2D. If we want to remove "full hwc composition" for "GL-hwc-mixed" composition, pref "layers.composer2d.enabled" just does it. Or we could remove HwcComposer2D::TryRenderWithHwc(). Even when composition is fully done by OpenGL(Compositor), its buffer is finally handled by hwc on android framework. In this case, HwcComposer2D::Render() is used to do it. The following is related diagram. https://github.com/sotaroikeda/firefox-diagrams/blob/master/widget/widget_GonkDisplayJB_FirefoxOS_3_0.pdf

(In reply to Alexandre LISSY :gerard-majax from comment #1) > Okay, digging into this I could see that on Gonk we have Hwc also handling > VSync. Should we also kill this ? We can not kill vsync handling. It is important for smooth rendering. It is used by VsyncSource. The following is a related diagram. https://github.com/sotaroikeda/firefox-diagrams/blob/master/gfx/gfx_VsyncSource_FirefoxOS_2_5.pdf

Sounds like getting rid of HWC would be more painful than keeping it around. Could we maybe just simplify it a bit?