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24 May 2024 : Day 242 #
It's funny how even when asleep I'm capable of making stupid mistakes. Yesterday I applied patch 0044 in order to restore the OnFirstPaint() trigger functionality. This is critical for getting the offscreen rendering pipeline to work. But as is the case after applying a patch I needed to rebuild the packages before they could be tested on my phone.

I kicked the build off to run overnight and then — d'oh! — promptly sent my laptop to sleep. It doesn't take a genius to realise that the build isn't going to run while the laptop is sleeping.

So here I am this morning without packages to test. At least my laptop is now awake and the build is continuing. But this has lost me the opportunity to do some development this morning.

Instead I've spent the time ordering myself a Jolla C2, the new Sailfish OS phone announced at Jolla Love Day 2 this last Monday. It's an interesting move by Jolla. For years now members of the community have been encouraging Jolla to offer Sailfish OS pre-installed. On the other hand, many in the community are also keen to see Sailfish OS offered on a very specific selection of handsets, be they PinePHones, Fairphones or brands that are more widely available in Europe, especially those known for being more "open".

My own opinion is that this is a good move by Jolla. There is no perfect phone and every choice has its benefits and drawbacks. Going with Sony phones all those years ago was controversial, but Sony hardware has (in my opinion) been both excellent and offering good value for the hardware. Nice materials, unassuming design and unexpectedly solid features (with headphones jacks, SD card slots, notification lights, and excellent screens to boot). Even more importantly Sony retained their commitment to openness over the long term, when other manufacturers have long since lost interest. On the other hand PinePhone and Fairphone have credentials that are really appealing for Sailfish users, who tend to prize openness and ethical considerations over price and features alone.

The new Reeder phone offers something a little different to either of these, which is the opportunity for Jolla to work hand-in-hand with the manufacturer. Jolla has a good track record doing this and the results historically have been very good. The new Reeder phone might not be open in the same way that the Sony or PinePhone are, but it's likely Jolla will have been given access to much more of what they need, including support, in order to build a really solid software experience for the hardware.

I'm speculating of course and only time will tell, but given we're still expecting Sailfish OS releases for the Xperia 10 IV and Xperia 10 V, and given I already have one of the latter, these are exciting times as far as I'm concerned.

Alright, let's get back to development. The build has carried on for a while but eventually failed with an error. Here's the debug output generated from the build process.
813:10.10 ${PROJECT}/gecko-dev/layout/base/nsRefreshDriver.cpp: In member 
    function ‘void nsRefreshDriver::Tick(mozilla::VsyncId, mozilla::TimeStamp, 
813:10.10 ${PROJECT}/gecko-dev/layout/base/nsRefreshDriver.cpp:2430:41: error: 
    ‘mNextTransactionId’ was not declared in this scope
813:10.10        transactionId.AppendInt((uint64_t)mNextTransactionId);
813:10.10                                          ^~~~~~~~~~~~~~~~~~
813:10.12 ${PROJECT}/gecko-dev/layout/base/nsRefreshDriver.cpp:2430:41: note: 
    suggested alternative: ‘GetTransactionId’
813:10.13        transactionId.AppendInt((uint64_t)mNextTransactionId);
813:10.13                                          ^~~~~~~~~~~~~~~~~~
813:10.13                                          GetTransactionId
813:14.49 make[4]: *** [${PROJECT}/gecko-dev/config/ 
    nsRefreshDriver.o] Error 1
The error is telling us that mNextTransactionIddoesn't exist and that's correct because it was removed by the patch. But there's still an instance remaining that the patch didn't capture. To get this through I've had to make one small change. This code looks to be related to profiling so probably isn't really needed for our purposes anyway, but we do need it to compile.
$ git diff layout/base/nsRefreshDriver.cpp
diff --git a/layout/base/nsRefreshDriver.cpp b/layout/base/nsRefreshDriver.cpp
index 33c90bb1f324..bb43dea053ea 100644
--- a/layout/base/nsRefreshDriver.cpp
+++ b/layout/base/nsRefreshDriver.cpp
@@ -2427,7 +2427,7 @@ void nsRefreshDriver::Tick(VsyncId aId, TimeStamp 
     nsCString transactionId;
     if (profiler_can_accept_markers()) {
       transactionId.AppendLiteral("Transaction ID: ");
-      transactionId.AppendInt((uint64_t)mNextTransactionId);
+      transactionId.AppendInt((uint64_t)mPendingTransaction);
         "ViewManagerFlush", GRAPHICS,
This is a similar change to that made elsewhere in the code, so should hopefully be pretty benign.

As the build is still taking a while I've decide I can't let all this potential development time go to waste. So I've decided to take the plunge and perform a test while the build continues. The current issue my most recent changes are aimed at addressing is the fact that the mIsPainted variable in the QMozViewPrivate class never gets set to true. So I'm wondering what will happen if I forcefully set it to true at a suitable time using the debugger.

If I'm honest I'm a little nervous about performing this test. If it turns out to have no effect then it'll leave me scratching my head yet again. I really want this rendering to work.

But I've plucked up the courage and am going to give it a go. First set the breakpoint on the method where the test for this flag is being made.
(gdb) b QuickMozView::updatePaintNode
Function "QuickMozView::updatePaintNode" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (QuickMozView::updatePaintNode) pending.
(gdb) r
Starting program: /usr/bin/harbour-webview
Now run the program through to the first time this breakpoint is hit. I don't want to flip the flag here because the rendering pipeline and textures aren't fully set up yet, so I'm going to wait for a later hit of the breakpoint.
Thread 9 "QSGRenderThread" hit Breakpoint 1, QuickMozView::
    updatePaintNode (this=0x555586dc20, oldNode=0x0) at quickmozview.cpp:172
172         if (width() <= 0 || height() <= 0) {
(gdb) c
=============== Preparing offscreen rendering context ===============
As we can see the rendering context has now been configured. Following this the breakpoint is hit again. Now is the time to change the flag from true to false. Here goes:
Thread 9 &quot;QSGRenderThread&quot; hit Breakpoint 1, QuickMozView::
    updatePaintNode (this=0x555586dc20, oldNode=0x7fc800c640) at 
172         if (width() <= 0 || height() <= 0) {
(gdb) p d->mIsPainted
$1 = false
(gdb) set d->mIsPainted = true
(gdb) p d->mIsPainted
$2 = true
(gdb) disable break
(gdb) c
Finally I disabled the breakpoint and set the program running again. And the result? I'm astonished to find that the result is a fully rendered Sailfish OS website!
A phone showing the website next to a laptop on a table with the debugger running in a console window.

Scrolling around, selecting links and interacting with the site all seem to work nicely. This is really encouraging. This means that once this patch is properly applied, that should be the final piece of the puzzle needed to get the WebView working again.
Three screenshots of the WebView rendering: the site at the top; the same site scrolled down a bit; and with the new Jolla C2 on display

I'm quite excited by this!

Unfortunately this is a debugging hack so we're not there yet. And the build has failed again. At least now, motivated by my excitement, I have plenty of energy to fix the build.

Here's the latest output from the failed build:
302:48.25 In file included from Unified_cpp_layout_base2.cpp:20:
302:48.25 ${PROJECT}/gecko-dev/layout/base/nsPresContext.cpp: In member 
    function ‘void nsPresContext::DetachPresShell()’:
302:48.25 ${PROJECT}/gecko-dev/layout/base/nsPresContext.cpp:843:15: error: 
    ‘class nsRootPresContext’ has no member named 
    ‘CancelApplyPluginGeometryTimer’; did you mean ‘mApplyPluginGeometryTimer’?
302:48.25      thisRoot->CancelApplyPluginGeometryTimer();
302:48.25                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
302:48.25                mApplyPluginGeometryTimer
302:48.40 ${PROJECT}/gecko-dev/layout/base/nsPresContext.cpp: In destructor 
    ‘virtual nsRootPresContext::~nsRootPresContext()’:
302:48.40 ${PROJECT}/gecko-dev/layout/base/nsPresContext.cpp:2683:3: error: 
    ‘CancelApplyPluginGeometryTimer’ was not declared in this scope
302:48.40    CancelApplyPluginGeometryTimer();
302:48.40    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
302:48.47 ${PROJECT}/gecko-dev/layout/base/nsPresContext.cpp:2683:3: note: 
    suggested alternative:  mApplyPluginGeometryTimer’
302:48.47    CancelApplyPluginGeometryTimer();
302:48.47    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
302:48.47    mApplyPluginGeometryTimer
302:48.51 ${PROJECT}/gecko-dev/layout/base/nsPresContext.cpp: In member 
    function ‘void nsRootPresContext::ComputePluginGeometryUpdates(nsIFrame*, 
    nsDisplayListBuilder*, nsDisplayList*)’:
302:48.51 ${PROJECT}/gecko-dev/layout/base/nsPresContext.cpp:2712:21: error: 
    ‘nsPluginFrame’ does not name a type; did you mean ‘nsPageFrame’?
302:48.51          static_cast<nsPluginFrame*>(iter.Get()->GetKey(
302:48.51                      ^~~~~~~~~~~~~
302:48.51                      nsPageFrame
These are actually rather odd errors. For example nsPageFrame has been added to the code even though it's not part of the upstream change. It must have been pulled in due to some changes applied later.

I'm not very happy with this, it's all a bit messy. So I've decided to revert my attempt to automatically merge in the patch and go back to a manual approach instead.

This will require a bit of a rework, which unfortunately I don't have time to do tonight. But I'll start on it in the morning and with any luck may be able to get it done tomorrow. Which means that's it for today. But we're definitely getting there!

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


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