1873123 - When WebRender samples a frame from APZ, have APZ provide all the information in one API call

Status: NEW

(Core :: Graphics: WebRender, task, P3)

Description

[Botond Ballo [:botond]]

Currently, when WebRender prepares to build a frame and samples async properties for that frame from APZ by calling apz_sample_transforms, APZ makes a number of WebRender API calls to provide the information being sampled:

• one call to wr_transaction_scroll_layer for every scroll frame to provide async scroll offsets
• (since bug 1604280) if the minimap is enabled, one call to wr_transaction_add_minimap_data for every scroll frame to provide minimap data
• one call to wr_transaction_set_is_transform_async_zooming to tell WebRender whether we are currently in an "async zoom" operation
• one call to wr_transaction_append_transform_properties to tell WebRender about APZ transforms (other than async scroll offsets) such as the zoom transform, and translation transforms applicable to fixed elements, sticky elements, and scrollbar thumbs

During the review of bug 1604280, Glenn suggested that we consider changing the API to provide all this information in a single API call.