Name Description Size 150942 51118 10564 8805 73609 Types and definitions related to compositing picture cache tiles and/or OS compositor integration. 37857 14840 117993 12381 11796
device 3 6061 7585 43590 A generic backing store for caches. `FreeList` is a simple vector-backed data structure where each entry in the vector contains an Option<T>. It maintains an index-based (rather than pointer-based) free list to efficiently locate the next unused entry. If all entries are occupied, insertion appends a new element to the vector. It also supports both strong and weak handle semantics. There is exactly one (non-Clonable) strong handle per occupied entry, which must be passed by value into `free()` to release an entry. Strong handles can produce an unlimited number of (Clonable) weak handles, which are used to perform lookups which may fail of the entry has been freed. A per-entry epoch ensures that weak handle lookups properly fail even if the entry has been freed and reused. TODO(gw): Add an occupied list head, for fast iteration of the occupied list to implement retain() style functionality. 8108 ! Gamma correction lookup tables. This is a port of Skia gamma LUT logic into Rust, used by WebRender. 14022 10209
glyph_rasterizer 1 Overview of the GPU cache. The main goal of the GPU cache is to allow on-demand allocation and construction of GPU resources for the vertex shaders to consume. Every item that wants to be stored in the GPU cache should create a GpuCacheHandle that is used to refer to a cached GPU resource. Creating a handle is a cheap operation, that does *not* allocate room in the cache. On any frame when that data is required, the caller must request that handle, via ```request```. If the data is not in the cache, the user provided closure will be invoked to build the data. After ```end_frame``` has occurred, callers can use the ```get_address``` API to get the allocated address in the GPU cache of a given resource slot for this frame. 32663 25104 21996 The interning module provides a generic data structure interning container. It is similar in concept to a traditional string interning container, but it is specialized to the WR thread model. There is an Interner structure, that lives in the scene builder thread, and a DataStore structure that lives in the frame builder thread. Hashing, interning and handle creation is done by the interner structure during scene building. Delta changes for the interner are pushed during a transaction to the frame builder. The frame builder is then able to access the content of the interned handles quickly, via array indexing. Epoch tracking ensures that the garbage collection step which the interner uses to remove items is only invoked on items that the frame builder thread is no longer referencing. Items in the data store are stored in a traditional free-list structure, for content access and memory usage efficiency. The epoch is incremented each time a scene is built. The most recently used scene epoch is stored inside each handle. This is then used for cache invalidation. 12220 21002 ! A GPU based renderer for the web. It serves as an experimental render backend for [Servo](, but it can also be used as such in a standalone application. # External dependencies WebRender currently depends on [FreeType]( # Api Structure The main entry point to WebRender is the [`crate::Renderer`]. By calling [`Renderer::new(...)`](crate::Renderer::new) you get a [`Renderer`], as well as a [`RenderApiSender`](api::RenderApiSender). Your [`Renderer`] is responsible to render the previously processed frames onto the screen. By calling [`yourRenderApiSender.create_api()`](api::RenderApiSender::create_api), you'll get a [`RenderApi`](api::RenderApi) instance, which is responsible for managing resources and documents. A worker thread is used internally to untie the workload from the application thread and therefore be able to make better use of multicore systems. ## Frame What is referred to as a `frame`, is the current geometry on the screen. A new Frame is created by calling [`set_display_list()`](api::Transaction::set_display_list) on the [`RenderApi`](api::RenderApi). When the geometry is processed, the application will be informed via a [`RenderNotifier`](api::RenderNotifier), a callback which you pass to [`Renderer::new`]. More information about [stacking contexts][stacking_contexts]. [`set_display_list()`](api::Transaction::set_display_list) also needs to be supplied with [`BuiltDisplayList`](api::BuiltDisplayList)s. These are obtained by finalizing a [`DisplayListBuilder`](api::DisplayListBuilder). These are used to draw your geometry. But it doesn't only contain trivial geometry, it can also store another [`StackingContext`](api::StackingContext), as they're nestable. [stacking_contexts]: 6870 A picture represents a dynamically rendered image. # Overview Pictures consists of: - A number of primitives that are drawn onto the picture. - A composite operation describing how to composite this picture into its parent. - A configuration describing how to draw the primitives on this picture (e.g. in screen space or local space). The tree of pictures are generated during scene building. Depending on their composite operations pictures can be rendered into intermediate targets or folded into their parent picture. ## Picture caching Pictures can be cached to reduce the amount of rasterization happening per frame. When picture caching is enabled, the scene is cut into a small number of slices, typically: - content slice - UI slice - background UI slice which is hidden by the other two slices most of the time. Each of these slice is made up of fixed-size large tiles of 2048x512 pixels (or 128x128 for the UI slice). Tiles can be either cached rasterized content into a texture or "clear tiles" that contain only a solid color rectangle rendered directly during the composite pass. ## Invalidation Each tile keeps track of the elements that affect it, which can be: - primitives - clips - image keys - opacity bindings - transforms These dependency lists are built each frame and compared to the previous frame to see if the tile changed. The tile's primitive dependency information is organized in a quadtree, each node storing an index buffer of tile primitive dependencies. The union of the invalidated leaves of each quadtree produces a per-tile dirty rect which defines the scissor rect used when replaying the tile's drawing commands and can be used for partial present. ## Display List shape WR will first look for an iframe item in the root stacking context to apply picture caching to. If that's not found, it will apply to the entire root stacking context of the display list. Apart from that, the format of the display list is not important to picture caching. Each time a new scroll root is encountered, a new picture cache slice will be created. If the display list contains more than some arbitrary number of slices (currently 8), the content will all be squashed into a single slice, in order to save GPU memory and compositing performance. ## Compositor Surfaces Sometimes, a primitive would prefer to exist as a native compositor surface. This allows a large and/or regularly changing primitive (such as a video, or webgl canvas) to be updated each frame without invalidating the content of tiles, and can provide a significant performance win and battery saving. Since drawing a primitive as a compositor surface alters the ordering of primitives in a tile, we use 'overlay tiles' to ensure correctness. If a tile has a compositor surface, _and_ that tile has primitives that overlap the compositor surface rect, the tile switches to be drawn in alpha mode. We rely on only promoting compositor surfaces that are opaque primitives. With this assumption, the tile(s) that intersect the compositor surface get a 'cutout' in the rectangle where the compositor surface exists (not the entire tile), allowing that tile to be drawn as an alpha tile after the compositor surface. Tiles are only drawn in overlay mode if there is content that exists on top of the compositor surface. Otherwise, we can draw the tiles in the normal fast path before the compositor surface is drawn. Use of the per-tile valid and dirty rects ensure that we do a minimal amount of per-pixel work here to blend the overlay tile (this is not always optimal right now, but will be improved as a follow up). 307891
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prim_store 9 2774 61424 The high-level module responsible for managing the pipeline and preparing commands to be issued by the `Renderer`. See the comment at the top of the `renderer` module for a description of how these two pieces interact. 80166 41704 59239 9956 This module contains the render task graph. Code associated with creating specific render tasks is in the render_task module. 31963 The high-level module responsible for interfacing with the GPU. Much of WebRender's design is driven by separating work into different threads. To avoid the complexities of multi-threaded GPU access, we restrict all communication with the GPU to one thread, the render thread. But since issuing GPU commands is often a bottleneck, we move everything else (i.e. the computation of what commands to issue) to another thread, the RenderBackend thread. The RenderBackend, in turn, may delegate work to other thread (like the SceneBuilder threads or Rayon workers), but the Render-vs-RenderBackend distinction is the most important. The consumer is responsible for initializing the render thread before calling into WebRender, which means that this module also serves as the initial entry point into WebRender, and is responsible for spawning the various other threads discussed above. That said, WebRender initialization returns both the `Renderer` instance as well as a channel for communicating directly with the `RenderBackend`. Aside from a few high-level operations like 'render now', most of interesting commands from the consumer go over that channel and operate on the `RenderBackend`. ## Space conversion guidelines At this stage, we shuld be operating with `DevicePixel` and `FramebufferPixel` only. "Framebuffer" space represents the final destination of our rendeing, and it happens to be Y-flipped on OpenGL. The conversion is done as follows: - for rasterized primitives, the orthographics projection transforms the content rectangle to -1 to 1 - the viewport transformation is setup to map the whole range to the framebuffer rectangle provided by the document view, stored in `DrawTarget` - all the direct framebuffer operations, like blitting, reading pixels, and setting up the scissor, are accepting already transformed coordinates, which we can get by calling `DrawTarget::to_framebuffer_rect` 296041 68657 12331 34340 154783 Screen capture infrastructure for the Gecko Profiler and Composition Recorder. 17527 Primitive segmentation # Overview Segmenting is the process of breaking rectangular primitives into smaller rectangular primitives in order to extract parts that could benefit from a fast paths. Typically this is used to allow fully opaque segments to be rendered in the opaque pass. For example when an opaque rectangle has a non-axis-aligned transform applied, we usually have to apply some anti-aliasing around the edges which requires alpha blending. By segmenting the edges out of the center of the primitive, we can keep a large amount of pixels in the opaque pass. Segmenting also lets us avoids rasterizing parts of clip masks that we know to have no effect or to be fully masking. For example by segmenting the corners of a rounded rectangle clip, we can optimize both rendering the mask and the primitive by only rasterize the corners in the mask and not applying any clipping to the segments of the primitive that don't overlap the borders. It is a flexible system in the sense that different sources of segmentation (for example two rounded rectangle clips) can affect the segmentation, and the possibility to segment some effects such as specific clip kinds does not necessarily mean the primitive will actually be segmented. ## Segments and clipping Segments of a primitive can be either not clipped, fully clipped, or partially clipped. In the first two case we don't need a clip mask. For each partially masked segments, a mask is rasterized using a render task. All of the interesting steps happen during frame building. - The first step is to determine the segmentation and write the associated GPU data. See `PrimitiveInstance::build_segments_if_needed` and `write_brush_segment_description` in `prim_store/` which uses the segment builder of this module. - The second step is to generate the mask render tasks. See `BrushSegment::update_clip_task` and `RenderTask::new_mask`. For each segment that needs a mask, the contribution of all clips that affect the segment is added to the mask's render task. - Segments are assigned to batches (See ``). Segments of a given primitive can be assigned to different batches. See also the [`clip` module documentation][] for details about how clipping information is represented. []: ../clip/index.html 44708 40489 41900 34942 3550 9941 77046 38741