Android(安卓)Framework层看硬件加速

Android 从Android3.0(API Level 11)开始就支持了硬件加速，在target api >= 14会默认开启，利用GPU代替CPU绘制，软加速是利用Skia，而硬件加速是利用OpenGL绘制。缺点是增加了内存占用。

本文只是在java层去看硬件加速，没有深究jni层如何绘制。

RenderNode 每个View都有一个RenderNode与之对应
RenderThread jin层会创建一个对应的线程，loop循环接收RenderNode
DisplayList jin层将DisplayListCanvas的操作转化到DisplayList
DisplayListCanvas java层上canvas缓存所有绘制操作，设置到RenderNode中

基本流程：

UI线程负责构建操作DisplayList
RenderThread线程利用OpenGL去绘制DisplayList的操作

参考之前的文章《View/ViewGroup 绘制流程和疑惑(一)》可以了解整个View/ViewGroup/ViewRootImpl整体的绘制流程。

硬件加速的绘制流程基本上是一致的，只不过在draw流程上有不同的分歧点。

我们知道，子View的invalidate标记dirty区域，借由着ViewParent的invalidateChildInParent(int[] location, Rect dirty)，到顶层的DecorView，最后触发了ViewRootImpl的invalidateChildInParent()，引起schedualTraversals()。

在文章《Android 屏幕刷新机制》讲过Vsync信号到来的时候，才会引起ViewRootImpl的preformTraversals()流程到draw()。

ThreadedRender初始化

在添加窗口WindowManagerGlobal.addView()会调用ViewRootlImpl的setView()

// WindowManagerGlobalpublic void addView(View view, ViewGroup.LayoutParams params,            Display display, Window parentWindow) {root.setView(view, wparams, panelParentView);}public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {if (mSurfaceHolder == null) {enableHardwareAcceleration(attrs);    }}private void enableHardwareAcceleration(WindowManager.LayoutParams attrs) {        mAttachInfo.mHardwareAccelerated = false;        mAttachInfo.mHardwareAccelerationRequested = false;        // 根据标记位，判断是否要硬件加速        final boolean hardwareAccelerated =                (attrs.flags & WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED) != 0;        if (hardwareAccelerated) {            // 是否支持硬件加速：判断是否支持OpenGL            if (!ThreadedRenderer.isAvailable()) {                return;            }            if (!ThreadedRenderer.sRendererDisabled                    || (ThreadedRenderer.sSystemRendererDisabled && forceHwAccelerated)) {                if (mAttachInfo.mThreadedRenderer != null) {                    mAttachInfo.mThreadedRenderer.destroy();                }                // 创建ThreadedRender                mAttachInfo.mThreadedRenderer = ThreadedRenderer.create(mContext, translucent,                        attrs.getTitle().toString());                          }        }    }public static ThreadedRenderer create(Context context, boolean translucent, String name) {    ThreadedRenderer renderer = null;    if (isAvailable()) {        renderer = new ThreadedRenderer(context, translucent, name);    }    return renderer;}ThreadedRenderer(Context context, boolean translucent, String name) {    // jni 创建 RenderNode    long rootNodePtr = nCreateRootRenderNode();    // 赋值给根布局的RenderNode    mRootNode = RenderNode.adopt(rootNodePtr);    // 创建ThreadProxy用来向RenderThread线程提交操作    mNativeProxy = nCreateProxy(translucent, rootNodePtr);}

View的RenderNode初始化

// View.javapublic View(Context context) {mRenderNode = RenderNode.create(getClass().getName(), this);}public static RenderNode create(String name, @Nullable View owningView) {    return new RenderNode(name, owningView);}private RenderNode(String name, View owningView) {    mNativeRenderNode = nCreate(name);    NoImagePreloadHolder.sRegistry.registerNativeAllocation(this, mNativeRenderNode);    mOwningView = owningView;}

Draw() 流程

private void draw(boolean fullRedrawNeeded) {    Surface surface = mSurface;    final Rect dirty = mDirty;    if (!dirty.isEmpty() || mIsAnimating || accessibilityFocusDirty) {        // 硬件加速        if (mAttachInfo.mThreadedRenderer != null && mAttachInfo.mThreadedRenderer.isEnabled()) {            boolean invalidateRoot = accessibilityFocusDirty || mInvalidateRootRequested;            mInvalidateRootRequested = false;            if (invalidateRoot) {                mAttachInfo.mThreadedRenderer.invalidateRoot();            }            mAttachInfo.mThreadedRenderer.draw(mView, mAttachInfo, this);        } else {        // 软件加速            if (!drawSoftware(surface, mAttachInfo, xOffset, yOffset, scalingRequired, dirty)) {                return;            }        }}

硬件加速：mAttachInfo.mThreadedRenderer.draw(mView, mAttachInfo, this)

软件加速：drawSoftware(surface, mAttachInfo, xOffset, yOffset, scalingRequired, dirty)

// ThreadedRender// view指向的DecorViewvoid draw(View view, AttachInfo attachInfo, DrawCallbacks callbacks) {    attachInfo.mIgnoreDirtyState = true;    final Choreographer choreographer = attachInfo.mViewRootImpl.mChoreographer;    choreographer.mFrameInfo.markDrawStart();    updateRootDisplayList(view, callbacks);    …    int syncResult = nSyncAndDrawFrame(mNativeProxy, frameInfo, frameInfo.length);}// 更新所有RenderNode 创建DisplayListCanvas赋值到RenderNodeprivate void updateRootDisplayList(View view, DrawCallbacks callbacks) {    updateViewTreeDisplayList(view);    if (mRootNodeNeedsUpdate || !mRootNode.isValid()) {        DisplayListCanvas canvas = mRootNode.start(mSurfaceWidth, mSurfaceHeight);        try {            final int saveCount = canvas.save();            canvas.translate(mInsetLeft, mInsetTop);            callbacks.onPreDraw(canvas);            canvas.insertReorderBarrier();            canvas.drawRenderNode(view.updateDisplayListIfDirty());            canvas.insertInorderBarrier();            callbacks.onPostDraw(canvas);            canvas.restoreToCount(saveCount);            mRootNodeNeedsUpdate = false;        } finally {            mRootNode.end(canvas);        }    }}//private void updateViewTreeDisplayList(View view) {    ...    view.updateDisplayListIfDirty();}

RenderedThread从DecorView开始，往所有的ViewGroup/View更新RenderNode

// View.javapublic RenderNode updateDisplayListIfDirty() {    final RenderNode renderNode = mRenderNode;    final DisplayListCanvas canvas = renderNode.start(width, height);    canvas.setHighContrastText(mAttachInfo.mHighContrastText);try {        if (layerType == LAYER_TYPE_SOFTWARE) {            buildDrawingCache(true);            Bitmap cache = getDrawingCache(true);            if (cache != null) {                canvas.drawBitmap(cache, 0, 0, mLayerPaint);            }        } else {           // 如果是ViewGroup，自身不用绘制，直接递归子View           if ((mPrivateFlags & PFLAG_SKIP_DRAW) == PFLAG_SKIP_DRAW) {               dispatchDraw(canvas);           } else {               draw(canvas);           }        }     } finally {        renderNode.end(canvas);        setDisplayListProperties(renderNode);     }     return renderNode;}public void end(DisplayListCanvas canvas) {    long displayList = canvas.finishRecording();    nSetDisplayList(mNativeRenderNode, displayList);    canvas.recycle();}

从RenderNode获取DisplayListCanvas，将所有操作写入到DisplayListCanvas，最后交给RenderNode，完成构建DisplayList。最后调用nSyncAndDrawFrame

参考：
https://www.jianshu.com/p/7bf306c09c7e
https://www.jb51.net/article/143618.htm

ThreadedRender初始化

View的RenderNode初始化

Draw() 流程

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