private void performDraw() {
final boolean fullRedrawNeeded = mFullRedrawNeeded;
mFullRedrawNeeded = false;
try {
draw(fullRedrawNeeded);
} finally {
}
}

 private void draw(boolean fullRedrawNeeded) {
if (mAttachInfo.mHardwareRenderer != null && mAttachInfo.mHardwareRenderer.isEnabled()) {
// If accessibility focus moved, always invalidate the root.
boolean invalidateRoot = accessibilityFocusDirty || mInvalidateRootRequested;
mInvalidateRootRequested = false;
// Draw with hardware renderer.
mIsAnimating = false;
if (mHardwareYOffset != yOffset || mHardwareXOffset != xOffset) {
mHardwareYOffset = yOffset;
mHardwareXOffset = xOffset;
invalidateRoot = true;
}
if (invalidateRoot) {
mAttachInfo.mHardwareRenderer.invalidateRoot();
}
dirty.setEmpty();
// Stage the content drawn size now. It will be transferred to the renderer
// shortly before the draw commands get send to the renderer.
final boolean updated = updateContentDrawBounds();
if (mReportNextDraw) {
// report next draw overrides setStopped()
// This value is re-sync'd to the value of mStopped
// in the handling of mReportNextDraw post-draw.
mAttachInfo.mHardwareRenderer.setStopped(false);
}
if (updated) {
requestDrawWindow();
}
mAttachInfo.mHardwareRenderer.draw(mView, mAttachInfo, this);
}
}

void draw(View view, AttachInfo attachInfo, HardwareDrawCallbacks callbacks) {
attachInfo.mIgnoreDirtyState = true;
final Choreographer choreographer = attachInfo.mViewRootImpl.mChoreographer;
choreographer.mFrameInfo.markDrawStart();
updateRootDisplayList(view, callbacks);
attachInfo.mIgnoreDirtyState = false;
}

 private void updateRootDisplayList(View view, HardwareDrawCallbacks callbacks) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "Record View#draw()");
updateViewTreeDisplayList(view);
if (mRootNodeNeedsUpdate || !mRootNode.isValid()) {
DisplayListCanvas canvas = mRootNode.start(mSurfaceWidth, mSurfaceHeight);
try {
final int saveCount = canvas.save();
canvas.translate(mInsetLeft, mInsetTop);
callbacks.onHardwarePreDraw(canvas);
canvas.insertReorderBarrier();
canvas.drawRenderNode(view.updateDisplayListIfDirty());
canvas.insertInorderBarrier();
callbacks.onHardwarePostDraw(canvas);
canvas.restoreToCount(saveCount);
mRootNodeNeedsUpdate = false;
} finally {
mRootNode.end(canvas);
}
}
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}

public RenderNode updateDisplayListIfDirty() {
if ((mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == 0
|| !renderNode.isValid()
|| (mRecreateDisplayList)) {
if (renderNode.isValid()
&& !mRecreateDisplayList) {
mPrivateFlags |= PFLAG_DRAWN | PFLAG_DRAWING_CACHE_VALID;
mPrivateFlags &= ~PFLAG_DIRTY_MASK;
dispatchGetDisplayList();
return renderNode; // no work needed
}
try {
if (layerType == LAYER_TYPE_SOFTWARE) {
buildDrawingCache(true);
Bitmap cache = getDrawingCache(true);
if (cache != null) {
canvas.drawBitmap(cache, 0, 0, mLayerPaint);
}
} else {
computeScroll();
canvas.translate(-mScrollX, -mScrollY);
mPrivateFlags |= PFLAG_DRAWN | PFLAG_DRAWING_CACHE_VALID;
mPrivateFlags &= ~PFLAG_DIRTY_MASK;
// Fast path for layouts with no backgrounds
if ((mPrivateFlags & PFLAG_SKIP_DRAW) == PFLAG_SKIP_DRAW) {
dispatchDraw(canvas);
if (mOverlay != null && !mOverlay.isEmpty()) {
mOverlay.getOverlayView().draw(canvas);
}
} else {
draw(canvas);
}
}
} finally {
renderNode.end(canvas);
setDisplayListProperties(renderNode);
}
} else {
mPrivateFlags |= PFLAG_DRAWN | PFLAG_DRAWING_CACHE_VALID;
mPrivateFlags &= ~PFLAG_DIRTY_MASK;
}
return renderNode;
}

未开启硬件加速View的绘制流程

private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff,
boolean scalingRequired, Rect dirty) {
Canvas
canvas = mSurface.lockCanvas(dirty);
mView.draw(canvas);
return true;
}
mSurface.lockCanvas(dirty);会调用如下代码：
public Canvas lockCanvas(Rect inOutDirty)
throws Surface.OutOfResourcesException, IllegalArgumentException {
Canvas mCanvas = new CompatibleCanvas();
return mCanvas;
}
}

ScrollView滑动流程分析

protected void onOverScrolled(int scrollX, int scrollY,
boolean clampedX, boolean clampedY) {
// Treat animating scrolls differently; see #computeScroll() for why.
if (!mScroller.isFinished()) {
final int oldX = mScrollX;
final int oldY = mScrollY;
mScrollX = scrollX;
mScrollY = scrollY;
invalidateParentIfNeeded();
onScrollChanged(mScrollX, mScrollY, oldX, oldY);
if (clampedY) {
mScroller.springBack(mScrollX, mScrollY, 0, 0, 0, getScrollRange());
}
} else {
super.scrollTo(scrollX, scrollY);
}
awakenScrollBars();
}

postInvalidateOnAnimationScroll来更新视图。
public void postInvalidateOnAnimation() {
// We try only with the AttachInfo because there's no point in invalidating
// if we are not attached to our window
final AttachInfo attachInfo = mAttachInfo;
if (attachInfo != null) {
attachInfo.mViewRootImpl.dispatchInvalidateOnAnimation(this);
}
}