upload android base code part8
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<html devsite>
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<head>
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<title>Graphics architecture</title>
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<meta name="project_path" value="/_project.yaml" />
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<meta name="book_path" value="/_book.yaml" />
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</head>
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<body>
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<!--
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Copyright 2017 The Android Open Source Project
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<p><em>What every developer should know about Surface, SurfaceHolder,
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EGLSurface, SurfaceView, GLSurfaceView, SurfaceTexture, TextureView,
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SurfaceFlinger, and Vulkan.</em></p>
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<p>This page describes essential elements of the Android system-level graphics
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architecture and how they are used by the application framework and multimedia
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system. The focus is on how buffers of graphical data move through the system.
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If you've ever wondered why SurfaceView and TextureView behave the way they do,
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or how Surface and EGLSurface interact, you are in the correct place.</p>
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<p>Some familiarity with Android devices and application development is assumed.
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You don't need detailed knowledge of the app framework and very few API calls
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are mentioned, but the material doesn't overlap with other public
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documentation. The goal is to provide details on the significant events
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involved in rendering a frame for output to help you make informed choices
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when designing an application. To achieve this, we work from the bottom up,
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describing how the UI classes work rather than how they can be used.</p>
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<p>This section includes several pages covering everything from background
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material to HAL details to use cases. It starts with an explanation of Android
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graphics buffers, describes the composition and display mechanism, then proceeds
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to the higher-level mechanisms that supply the compositor with data. We
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recommend reading pages in the order listed below rather than skipping to a
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topic that sounds interesting.</p>
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<h2 id=low_level>Low-level components</h2>
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<ul>
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<li><a href="/devices/graphics/arch-bq-gralloc.html">BufferQueue and
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gralloc</a>. BufferQueue connects something that generates buffers of graphical
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data (the <em>producer</em>) to something that accepts the data for display or
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further processing (the <em>consumer</em>). Buffer allocations are performed
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through the <em>gralloc</em> memory allocator implemented through a
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vendor-specific HAL interface.</li>
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<li><a href="/devices/graphics/arch-sf-hwc.html">SurfaceFlinger,
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Hardware Composer, and virtual displays</a>. SurfaceFlinger accepts buffers of
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data from multiple sources, composites them, and sends them to the display. The
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Hardware Composer HAL (HWC) determines the most efficient way to composite
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buffers with the available hardware, and virtual displays make composited output
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available within the system (recording the screen or sending the screen over a
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network).</li>
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<li><a href="/devices/graphics/arch-sh.html">Surface, Canvas, and
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SurfaceHolder</a>. A Surface produces a buffer queue that is often consumed by
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SurfaceFlinger. When rendering onto a Surface, the result ends up in a buffer
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that gets shipped to the consumer. Canvas APIs provide a software implementation
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(with hardware-acceleration support) for drawing directly on a Surface
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(low-level alternative to OpenGL ES). Anything having to do with a View involves
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a SurfaceHolder, whose APIs enable getting and setting Surface parameters such
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as size and format.</li>
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<li><a href="/devices/graphics/arch-egl-opengl.html">EGLSurface and
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OpenGL ES</a>. OpenGL ES (GLES) defines a graphics-rendering API designed to be
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combined with EGL, a library that knows how to create and access windows through
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the operating system (to draw textured polygons, use GLES calls; to put
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rendering on the screen, use EGL calls). This page also covers ANativeWindow,
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the C/C++ equivalent of the Java Surface class used to create an EGL window
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surface from native code.</li>
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<li><a href="/devices/graphics/arch-vulkan.html">Vulkan</a>. Vulkan is
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a low-overhead, cross-platform API for high-performance 3D graphics. Like OpenGL
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ES, Vulkan provides tools for creating high-quality, real-time graphics in
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applications. Vulkan advantages include reductions in CPU overhead and support
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for the <a href="https://www.khronos.org/spir">SPIR-V Binary Intermediate</a>
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language.</li>
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</ul>
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<h2 id=high_level>High-level components</h2>
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<ul>
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<li><a href="/devices/graphics/arch-sv-glsv.html">SurfaceView and
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GLSurfaceView</a>. SurfaceView combines a Surface and a View. SurfaceView's View
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components are composited by SurfaceFlinger (and not the app), enabling
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rendering from a separate thread/process and isolation from app UI rendering.
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GLSurfaceView provides helper classes to manage EGL contexts, inter-thread
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communication, and interaction with the Activity lifecycle (but is not required
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to use GLES).</li>
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<li><a href="/devices/graphics/arch-st.html">SurfaceTexture</a>.
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SurfaceTexture combines a Surface and GLES texture to create a BufferQueue for
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which your app is the consumer. When a producer queues a new buffer, it notifies
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your app, which in turn releases the previously-held buffer, acquires the new
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buffer from the queue, and makes EGL calls to make the buffer available to GLES
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as an external texture. Android 7.0 adds support for secure texture video
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playback enabling GPU post-processing of protected video content.</li>
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<li><a href="/devices/graphics/arch-tv.html">TextureView</a>.
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TextureView combines a View with a SurfaceTexture. TextureView wraps a
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SurfaceTexture and takes responsibility for responding to callbacks and
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acquiring new buffers. When drawing, TextureView uses the contents of the most
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recently received buffer as its data source, rendering wherever and however the
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View state indicates it should. View composition is always performed with GLES,
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meaning updates to contents may cause other View elements to redraw as well.</li>
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</ul>
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</body>
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</html>
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