What are the thick orange borders when "Show layer borders" is enabled in DevTools?

[Xianzhu Wang]

Hi, graphics-dev,

When I enable "Show layer borders" in the Rendering panel in DevTools, there are thick orange borders shown in the page, see this video. I see them on Windows, Mac and ChromeOS, but not Linux through remote desktop. I don't think they are layer borders or tile borders. Is there a document about them?

Thanks,

Xianzhu

[Sunny Sachanandani]

Maybe you can try matching the color with the predefined ones in debug_colors.cc. There are several orange like colors there though :/

[Xianzhu Wang]

There are 4 orange like colors:

1 TiledContentLayerBorderColor

2 SurfaceDamageRectBorderColor

3 NonFastScrollableRectBorderColor

4 MainThreadScrollingReasonRectBorderColor

The thick orange borders I see are not 1, 3 or 4. Suspected 2, but the thick orange borders are obviously different from what I see with --show-surface-damage-rects on Linux. There are also no debug borders with such a thick width (>=5 pixels).

I want to understand them because they look very annoying when I just want to see layer borders.

[Xianzhu Wang]

I bisected on Mac to https://chromium.googlesource.com/chromium/src/+log/7b74f72619ebc25c86e3cc09a407d1e43ca80ee7..612daee53a0c8a3aa91881e5eb799e752f0586c0 which includes the CL to enable SkiaRenderer on Mac.

I debugged a bit and found that the color used is TiledContentLayerBorderColor to show layer borders for tiled layers, but the borders shown are obviously incorrect. Filed crbug.com/1354009.