android Surface概述

Surface的主要作用是存储View树的绘制数据，主要由屏幕组合器管理（screen compositor），每个Window都有一个Surface。

android中Surface分为两种：

一、Java层surface

二、Native层Surface

Java层产生Surface的主要有两个地方：ViewRoot和SurfaceView。

Native层主要由NativeWindow产生。

Surface是如何和View树搭上关系的呢？

不过相信大家对View中的draw（）方法一定很熟悉！

   boolean draw(Canvas canvas, ViewGroup parent, long drawingTime) {      }   protected void onDraw(Canvas canvas) {     }

draw里面的Canvas都是由Framework传递来的参数，那么Canvas就是View树和Surface的连接点。

View树的测绘（measure）、布局（layout）和绘制（draw）都是由ViewRoot发起和管理的，View树绘制起点由ViewRoot的drawSoftware开始的！

drawSoftware的方法体大致如下：

 private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff,            boolean scalingRequired, Rect dirty) {        // Draw with software renderer.        final Canvas canvas;          canvas = mSurface.lockCanvas(dirty);//获取Canvas        try {            if (!canvas.isOpaque() || yoff != 0 || xoff != 0) {                canvas.drawColor(0, PorterDuff.Mode.CLEAR);            }            dirty.setEmpty();            mIsAnimating = false;            attachInfo.mDrawingTime = SystemClock.uptimeMillis();            mView.mPrivateFlags |= View.PFLAG_DRAWN;            if (DEBUG_DRAW) {                Context cxt = mView.getContext();            }            try {                canvas.translate(-xoff, -yoff);                if (mTranslator != null) {                    mTranslator.translateCanvas(canvas);                }                canvas.setScreenDensity(scalingRequired ? mNoncompatDensity : 0);                attachInfo.mSetIgnoreDirtyState = false;                mView.draw(canvas);//绘制view树                drawAccessibilityFocusedDrawableIfNeeded(canvas);            } finally {                if (!attachInfo.mSetIgnoreDirtyState) {                    // Only clear the flag if it was not set during the mView.draw() call                    attachInfo.mIgnoreDirtyState = false;                }            }        } finally {            try {                surface.unlockCanvasAndPost(canvas);            } catch (IllegalArgumentException e) {                Log.e(TAG, "Could not unlock surface", e);                mLayoutRequested = true;    // ask wm for a new surface next time.                //noinspection ReturnInsideFinallyBlock                return false;            }        }        return true;    }

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