1608875 - Merge uMode parameter with the shader program in WebRender

Status: NEW

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

Description

[Dzmitry Malyshau [:kvark]]

uMode is a uniform parameter that controls the mode of execution for brush_image and ps_text_run shaders. It changes the execution code path of these programs, and it's uniform across a batch. Effectively, speaking modern terms, it's a program specialization parameter. This leads Szeged team to treat it as such - https://github.com/szeged/webrender/issues/345 , which allows the Vulkan-based implementation to not have any per-batch uniform constants.

In order to reduce the difference with the Szeged branch, we could make uMode a part of the bind_program signature.