flypig.co.uk

I've spent this last week participating in a HackWeek. Organised at my place of work for the Research Engineering Group I'm part of, it allowed us to work with a different team on different projects and with different technologies than we usually would do.

My team developed a "Plantcraft" simulation, built on a three-dimensional grid where each cell satisfies a small set of physical rules approximating those of reality. A cell can be one of Air, Soil, Rock or Plant, each with a state that determines its water content, energy level, colour and memory. Despite the naming the four types of cell are actually identical, save for the state values and the fact that Plant cells execute a state-machine programme which determines their behaviour.

If you're interested all the documentation and executable code is available in the project's git repository. Please don't judge the code too harshly: it was all written under tight time constraints!
 
While it was huge fun to work with such a great team during the week, it's also nice to now be getting back to gecko once again. Time to get things moving and maybe apply some of the pressure of a time-constrained project to getting the gecko changes over the line too.

Let's recap where we were at last weekend before I paused during the week. I'll be continuing to work on getting WebGL rendering once again. The WebGL code was working nicely at one point, but since it makes use of the same offscreen rendering pipeline as the WebView, the changes I made to get the latter working seem to have broken the former.

I've already established and tweaked some of the relevant changes, namely that TileGenFunc() now executes CreateBasicTextureImage() in all circumstances and GLContext::ResizeScreenBuffer() now acts on SwapChain rather than GLScreenBuffer. Here's the full diff showing the changes I've made up to now to reverse these:

$ git diff
diff --git a/gfx/gl/GLContext.cpp b/gfx/gl/GLContext.cpp
index 1177768bb92e..aac6912bb914 100644
--- a/gfx/gl/GLContext.cpp
+++ b/gfx/gl/GLContext.cpp
@@ -1875,7 +1875,8 @@ void GLContext::MarkDestroyed() {
 
   // Null these before they're naturally nulled after dtor, as we want 
    GLContext
   // to still be alive in *their* dtors.
-  mScreen = nullptr;
+  //mScreen = nullptr;
+  mSwapChain = nullptr;
   mBlitHelper = nullptr;
   mReadTexImageHelper = nullptr;
 
@@ -1886,7 +1887,7 @@ void GLContext::MarkDestroyed() {
 bool GLContext::ResizeScreenBuffer(const gfx::IntSize& size) {
   if (!IsOffscreenSizeAllowed(size)) return false;
 
-  return mScreen->Resize(size);
+  return mSwapChain->Resize(size);
 }
 // -
 
diff --git a/gfx/gl/GLTextureImage.cpp b/gfx/gl/GLTextureImage.cpp
index c2def2dedb18..8152128bdc9c 100644
--- a/gfx/gl/GLTextureImage.cpp
+++ b/gfx/gl/GLTextureImage.cpp
@@ -47,6 +47,9 @@ already_AddRefed<TextureImage> CreateTextureImage(
 static already_AddRefed<TextureImage> TileGenFunc(
     GLContext* gl, const IntSize& aSize, TextureImage::ContentType 
    aContentType,
     TextureImage::Flags aFlags, TextureImage::ImageFormat aImageFormat) {
+  return CreateBasicTextureImage(gl, aSize, aContentType,
+                                 LOCAL_GL_CLAMP_TO_EDGE, aFlags);
+
   switch (gl->GetContextType()) {
     case GLContextType::EGL:
       return TileGenFuncEGL(gl, aSize, aContentType, aFlags, aImageFormat);

As I left things last weekend these changes were triggering a segfault. My task for today is to check the backtrace of the crash. It's bound to reveal something useful...

But oddly it doesn't. Or it might have were it not for the fact there's no crash after all. So since there's no backtrace I've had to go with a different approach. Instead I've been through the diff of the previous commit again to see whether it reveals any further gentle differences I can try to reverse. Ones that are unlikely to cause damage while at the same time might help resolve the WebGL issue.

One such change can be found in the SurfaceFactory constructor. This accepts an allocator and a flags parameter, neither of which appear to be used. So I've removed them to see what happens, setting the allocator to be nullptr where it's needed later instead.

Here's the diff of the changes I made:

diff --git a/gfx/gl/SharedSurface.cpp b/gfx/gl/SharedSurface.cpp
index 687d18b95893..1d911b84379a 100644
--- a/gfx/gl/SharedSurface.cpp
+++ b/gfx/gl/SharedSurface.cpp
[...]
@@ -149,10 +164,105 @@ UniquePtr<SurfaceFactory> SurfaceFactory::Create(
   return nullptr;
 }
 
-SurfaceFactory::SurfaceFactory(const PartialSharedSurfaceDesc& partialDesc)
-    : mDesc(partialDesc), mMutex(&quot;SurfaceFactor::mMutex&quot;) {}
+SurfaceFactory::SurfaceFactory(const PartialSharedSurfaceDesc& partialDesc,
+                               const RefPtr<layers::LayersIPCChannel>& 
    allocator,
+                               const layers::TextureFlags& flags)
+    : mDesc(partialDesc),
+      mAllocator(allocator),
+      mFlags(flags),
+      mMutex(&quot;SurfaceFactor::mMutex&quot;)
+{
+}
[...]

Changing, building, installing and testing this doesn't result in any change. The browser and WebView both work as before, but the WebGL functionality is still broken.

Given that I'm not getting a crash and that the various changes I've made today haven't had any apparent effect, tomorrow I'm going to go through the methods in the previous commit again, set breakpoints on them and see which are being used by the browser. Hopefully this will shed more light, while also giving me the opportunity to refresh my memory about the changes. A refresh is going to be helpful given I spent last week thinking about other things.

So, more on this tomorrow.

If you'd like to read any of my other gecko diary entries, they're all available on my Gecko-dev Diary page.