1888096 - (blob-layerization) [meta] [project] Improve the blob layerization algorithm

Status: NEW

(Core :: Graphics: WebRender, enhancement)

Description

[Nicolas Silva [:nical]]

The current blob layerization algorithm has some very bad performance cliffs. It has to strike a balance between favoring webrender display items over using software rasterization, and avoiding to allocate too many layers.

We get into trouble when the algorithm ends up allocating many layers because:

• it can require an unbounded amount of memory to be allocated (For example bug 1743190)
• it causes heavy jank during texture upload

A better layerization algorithm would:

• Take item overlap into account to decide whether to add to an existing layer or create a new one. It could use something similar to webrender's batching algorithm to achieve that.
• Take into consideration whether using webrender display items would cause extra overlapping layers and weight that against the cost of rasterizing the display item via the software fallback (its area).
• Enforce an upper bound on the total number of layers