| width | 渲染通道表面的宽度（以像素为单位）。 |
| height | 渲染通道表面的高度（以像素为单位）。 |
| samples | MSAA 样本数；设置为 1 以禁用抗锯齿。 |
| attachments | 渲染通道中使用的颜色附件数组。数组中的值会立即复制。 |
| depthAttachmentIndex | 用作此渲染通道的深度/模板缓冲区的附件索引，或为 -1 以禁用深度/模板。 |
| subPasses | Array containing information of each subpass. The values in the array are copied immediately. |
Begin a new native render pass.
The render pass allows multiple subpasses within the same renderpass, where the pixel shaders have a read access to the current pixel value within the renderpass. This allows for efficient implementation of various rendering methods on tile-based GPUs, such as deferred rendering.
渲染通道在 Metal (iOS) 和 Vulkan 上原生实现，但 API 能够通过仿真在所有渲染后端上完全正常运行（使用旧版 SetRenderTargets 调用并通过纹素抓取读取当前像素值）。
渲染通道机制具有以下限制：
- 所有附件必须拥有相同的分辨率和 MSAA 样本数
- The rendering results of previous subpasses are only available within the same screen-space pixel
coordinate via the UNITY_READ_FRAMEBUFFER_INPUT(x) macro in the shader; the attachments cannot be bound as textures or otherwise accessed until the renderpass has ended
- iOS Metal 不允许从 Z 缓冲区读取，因此需要其他渲染目标来执行这项操作
- The maximum amount of attachments allowed per render pass is currently 8 + depth, but note that various GPUs may have stricter limits.
The first subpass is started implictly upon calling this function with following subpasses activating upon NextSubPass.
After the last subpass has been scheduled, you need to close the render pass using EndRenderPass.
Only one render pass can be active at any time.
Additional resources: EndRenderPass, NextSubPass.