Surface lifecycle

We mentioned earlier that Wayland is designed to update everything atomically, such that no frame is ever presented in an invalid or intermediate state. Of the many attributes that can be configured for an application window and other surfaces, the driving mechanism behind that atomicity is the wl_surface itself.

我们之前提过，Wayland 旨在以原子性的方式更新所有内容，因此不会出现任何一帧处于无效 或中间状态。在为应用程序窗口和其他 surface 配置种种属性的过程中，背后的原子性是基于 wl_surface 驱动的。

Every surface has a pending state and an applied state, and no state at all when it’s first created. The pending state is negotiated over the course of any number of requests from clients and events from the server, and when both sides agree that it represents a consistent surface state, the surface is committed — and the pending state is applied to the current state of the surface. Until this time, the compositor will continue to render the last consistent state; once committed, will use the new state from the next frame forward.

除了第一次创建时没有状态，每个 surface 对象都有一个 pending 状态和一个 applied 状态。 挂起 状态作用于客户端的任意数量的请求和服务端对应的事件的协商（交互）过程，当双方一致 同意它（pending state）所代表的 surface 状态时，surface被 提交——并且挂起状态被应用于 当前表面状态。直到这个时候，合成器才会继续基于之前协商一致的状态进行渲染相关操作；（应用程序） 一旦提交完成，（合成器）将在下一帧显示给用户之前使用新状态。

Among the state which is updated atomically are:

需要原子更新的状态包括：

  • The attached wl_buffer, or the pixels making up the content of the surface
  • The region which was “damaged” since the last frame, and needs to be redrawn
  • The region which accepts input events
  • The region considered opaque1
  • Transformations on the attached wl_buffer, to rotate or present a subset of the buffer

  • The scale factor of the buffer, used for HiDPI displays

  • 附加的 wl_buffer，或构成表面内容的像素
  • 基于上一帧来说的 “损坏” 的区域，也就是需要重新绘制的区域
  • 能够接受输入事件的区域
  • 被认为不透明的区域1
  • 对附加的 wl_buffer 进行转换，以旋转或裁剪的方式呈现缓冲区
  • 缓冲区的缩放因子，用于 HiDPI 显示器

In addition to these features of the surface, the surface’s role may have additional double-buffered state like this. All of this state, along with any state associated with the role, is applied when wl_surface.commit is sent. You can send these requests several times if you change your mind, and only the most recent value for any of these properties will be considered when the surface is eventually committed.

表面不仅有这些特征，表面的 角色 可能还有像这样的额外的双缓冲状态。在发送 wl_surface.commit 时， surface 会应用所有这些状态以及与角色关联的任何状态。如果你需要修改这些状态，可以多次发送这些请求， 在最终提交 surface 时，只会考虑这些属性设置中的最新值。

When you first create your surface, the initial state is invalid. To make it valid (or to map the surface), you need to provide the necessary information to build the first consistent state for that surface. This includes giving it a role (like xdg_toplevel), allocating and attaching a buffer, and configuring any role-specific state for that surface. When you send a wl_surface.commit with this state correctly configured, the surface becomes valid (or mapped) and will be presented by the compositor.

首次创建 surface 时，初始状态无效。为了使其有效（或 映射 表面），你需要提供必要的 信息来为该表面构建第一个一致状态。 这包括为其赋予角色（如 xdg_toplevel）、分配和附加缓冲区， 以及为该表面配置任何特定于角色的状态。 当你正确配置状态，并发送 wl_surface.commit 时， 表面变为有效（或 映射）并将由合成器呈现。

The next question is: when should I prepare a new frame?

下一个问题是：我应该什么时候准备一个新的帧？

1：用于合成器优化（合成逻辑）。

原文链接:https://wayland-book.com/

  1. This is used by the compositor for optimization purposes. ↩ ↩2 ↩3