fix: set window contents as opaque to decrease DWM GPU usage

[brhenrique]

Description of Change

The window contents of Electron windows are marked as transparent even though neither transparent nor opacity settings are set in the BrowserWindow options.

Debugging DirectComposition redraws

Chromium 118 has a new flag called DCompDebugVisualization that uses EnableDrawRegions to display on the screen sections of a window that are redrawn by DirectComposition.

The problem

With DCompDebugVisualization, we can notice a difference in the frequency of redraws of <video> elements in Chromium compared to a regular non-transparent window in Electron.

While a video stream is rendered on screen, almost no redraws are displayed in Chromium. On Electron, a redraw is displayed for every video frame rendered.

Electron Fiddle gist: https://gist.github.com/brhenrique/100fc28409508d1730fb4216268cf04a

Why it happens?

When the contents of the window are set to be transparent, DirectCompositionChildSurfaceWin::SetDrawRectangle will use DXGI_ALPHA_MODE_PREMULTIPLIED instead of DXGI_ALPHA_MODE_IGNORE. This will trigger the DC redraw for every video frame.

Solution

If neither transparent nor opacity settings are used with a BrowserWindow, it seems safe to assume the contents of the BrowserWindow won't need alpha blending with other windows. So in this PR we override ShouldWindowContentsBeTransparent to take into account the transparency and opacity settings of the native window.

Results

Rendering 4 480p video elements in a blank opaque non-fullscreen Electron window on a 2160p display

Before: DWM uses 16-18% GPU
After: DWM uses less than 1%

Rendering 4 480p video elements in a blank opaque non-fullscreen Electron window on a 1080p display

Before: DWM uses 6-8% GPU
After: DWM uses less than 1%

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• relevant documentation, tutorials, templates and examples are changed or added
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: prevent DWM from redrawing video frames rendered on opaque windows

[deepak1556]

Thanks for the detailed analysis!

In case of Electron the title bar are system drawn unlike Chrome, so we get the default behavior defined in https://source.chromium.org/chromium/chromium/src/+/main:ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc;l=533-538. Do we regress with undrawn regions in the titlebar with this change ?

[brhenrique]

Thanks for the detailed analysis!

In case of Electron the title bar are system drawn unlike Chrome, so we get the default behavior defined in https://source.chromium.org/chromium/chromium/src/+/main:ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc;l=533-538. Do we regress with undrawn regions in the titlebar with this change ?

Yeah I got a bit confused by that comment because I couldn't remember of any app that draws underneath the title bar. Looking further back the commit history, this setting seems to originally come from a requirement from Aero Glass (removed on W8+)

https://codereview.chromium.org/2487893002/diff/1/ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc

Maybe this could be an issue if there was some code using DwmExtendFrameIntoClientArea to extend the client area to invade the title bar (never tried that so not sure if it's possible), but I couldn't find any place where this function is used that way in Electron.

Tried this PR with backgroundMaterial: acrylic, no issues there as well. titleBarStyle: hidden and titleBarOverlay: true also seem to work fine.

[MarshallOfSound]

@brhenrique can you rebase on latest main to pull in the depot_tools CI fixes

[brhenrique]

@brhenrique can you rebase on latest main to pull in the depot_tools CI fixes

@MarshallOfSound sure, done. Now appveyor: win-woa-testing failed but I couldn't find in the CI logs which test failed 🤔

[release-clerk]

Release Notes Persisted

Fixed opaque window performance regression on DWM

[trop]

I have automatically backported this PR to "27-x-y", please check out #40003