1973818 - With zoom, tall pages show gaps in surface tiles

Status: NEW

(Core :: Graphics: WebRender, defect)

Description

[Brad Werth [:bradwerth]]

On sites like https://worlds-highest-website.com, which is a very tall page, if the user zooms in, the bottom of the page shows gaps in the surface tiles. Before the landing of Bug 1971296, this would also crash the browser on macOS.

WebRender has rounding errors which are checked by a debug_assert. This crashes debug build before they can show the rendering problem. We need a solution that ensures correct rendering in all build types.

Comment 1

[Glenn Watson [:gw]]

Marking as an S3 for now, since it's likely quite rare. However, we do need a proper long term solution for this, and it's (probably) a non-trivial amount of work. I suspect the end result will be converting tile units throughout WR to be some kind of 64-bit fixed point int with some number of bits specified for subpixel fractions.

Comment 2

[Brad Werth [:bradwerth]]

Attachment: Tile gap at bottom of page

This shows an example of the tile gap. It also shows the problem we have with glyph box-shifting we have on tall pages, which is some other Bug I can't find right now.