始终很好奇鼠标光标是如何实现的,它反映很快、提早很小,没有受到 Android 显示零碎的影响。正好最近做相干的工作,跟着源码好好钻研一下。
本文参考 Android 9.0 源码。
从 Input 说起
咱们并不是要讲 Input,只想看看鼠标光标的绘制过程。然而,Android 将鼠标光标的实现放到了 Input 中,这看起来也是正当的。在 Input 中,光标由类Sprite
实现。源码中对 Sprite
的解释为:显示在其余图层之上的图形对象。看来 Sprite
并非专为光标设计,但在源码中的地位表明,它在 Android 中也只为鼠标或触摸之类的输出设施的光标服务。Sprite
的定义中也只提供了简略的图形操作。
frameworks/base/libs/input/SpriteController.h
/*
* A sprite is a simple graphical object that is displayed on-screen above other layers.
* The basic sprite class is an interface.
* The implementation is provided by the sprite controller.
*/
class Sprite : public RefBase {
protected:
Sprite() { }
virtual ~Sprite() { }
public:
enum {
// The base layer for pointer sprites.
BASE_LAYER_POINTER = 0, // reserve space for 1 pointer
// The base layer for spot sprites.
BASE_LAYER_SPOT = 1, // reserve space for MAX_POINTER_ID spots
};
/* Sets the bitmap that is drawn by the sprite.
* The sprite retains a copy of the bitmap for subsequent rendering. */
virtual void setIcon(const SpriteIcon& icon) = 0;
inline void clearIcon() {
setIcon(SpriteIcon());
}
/* Sets whether the sprite is visible. */
virtual void setVisible(bool visible) = 0;
/* Sets the sprite position on screen, relative to the sprite's hot spot. */
virtual void setPosition(float x, float y) = 0;
/* Sets the layer of the sprite, relative to the system sprite overlay layer.
* Layer 0 is the overlay layer, > 0 appear above this layer. */
virtual void setLayer(int32_t layer) = 0;
/* Sets the sprite alpha blend ratio between 0.0 and 1.0. */
virtual void setAlpha(float alpha) = 0;
/* Sets the sprite transformation matrix. */
virtual void setTransformationMatrix(const SpriteTransformationMatrix& matrix) = 0;
};
管制光标的类叫做 SpriteController
,PointerController 会应用这个类来显示光标。这里咱们只关怀光标图形的合成,真正显示和更新光标的办法是 SpriteController::doUpdateSprites()
。
frameworks/base/libs/input/SpriteController.cpp
void SpriteController::doUpdateSprites() {
// 从invalidatedSprites 中收集须要更新的 Sprite
Vector<SpriteUpdate> updates;
size_t numSprites;
{ // acquire lock
AutoMutex _l(mLock);
numSprites = mLocked.invalidatedSprites.size();
for (size_t i = 0; i < numSprites; i++) {
const sp<SpriteImpl>& sprite = mLocked.invalidatedSprites.itemAt(i);
updates.push(SpriteUpdate(sprite, sprite->getStateLocked()));
sprite->resetDirtyLocked();
}
mLocked.invalidatedSprites.clear();
} // release lock
// surfaces 未创立或失落时,从新创立 surface
bool surfaceChanged = false;
for (size_t i = 0; i < numSprites; i++) {
SpriteUpdate& update = updates.editItemAt(i);
if (update.state.surfaceControl == NULL && update.state.wantSurfaceVisible()) {
update.state.surfaceWidth = update.state.icon.bitmap.width();
update.state.surfaceHeight = update.state.icon.bitmap.height();
update.state.surfaceDrawn = false;
update.state.surfaceVisible = false;
// 创立 Surface,咱们这次的关注点
update.state.surfaceControl = obtainSurface(
update.state.surfaceWidth, update.state.surfaceHeight);
if (update.state.surfaceControl != NULL) {
update.surfaceChanged = surfaceChanged = true;
}
}
}
// 如果须要,从新调整 sprites 大小
SurfaceComposerClient::Transaction t;
bool needApplyTransaction = false;
for (size_t i = 0; i < numSprites; i++) {
......
if (update.state.surfaceWidth < desiredWidth
|| update.state.surfaceHeight < desiredHeight) {
needApplyTransaction = true;
t.setSize(update.state.surfaceControl,
desiredWidth, desiredHeight);
......
}
}
}
if (needApplyTransaction) {
t.apply();
}
// 如果须要,重画 sprites
for (size_t i = 0; i < numSprites; i++) {
SpriteUpdate& update = updates.editItemAt(i);
if ((update.state.dirty & DIRTY_BITMAP) && update.state.surfaceDrawn) {
update.state.surfaceDrawn = false;
update.surfaceChanged = surfaceChanged = true;
}
if (update.state.surfaceControl != NULL && !update.state.surfaceDrawn
&& update.state.wantSurfaceVisible()) {
sp<Surface> surface = update.state.surfaceControl->getSurface();
ANativeWindow_Buffer outBuffer;
......
// 应用 SKIA 画图
SkBitmap surfaceBitmap;
ssize_t bpr = outBuffer.stride * bytesPerPixel(outBuffer.format);
surfaceBitmap.installPixels(SkImageInfo::MakeN32Premul(outBuffer.width, outBuffer.height),
outBuffer.bits, bpr);
SkCanvas surfaceCanvas(surfaceBitmap);
SkPaint paint;
paint.setBlendMode(SkBlendMode::kSrc);
surfaceCanvas.drawBitmap(update.state.icon.bitmap, 0, 0, &paint);
if (outBuffer.width > update.state.icon.bitmap.width()) {
paint.setColor(0); // transparent fill color
surfaceCanvas.drawRect(SkRect::MakeLTRB(update.state.icon.bitmap.width(), 0,
outBuffer.width, update.state.icon.bitmap.height()), paint);
}
if (outBuffer.height > update.state.icon.bitmap.height()) {
paint.setColor(0); // transparent fill color
surfaceCanvas.drawRect(SkRect::MakeLTRB(0, update.state.icon.bitmap.height(),
outBuffer.width, outBuffer.height), paint);
}
......
}
// 依据 dirty 值来设置 Surface
needApplyTransaction = false;
for (size_t i = 0; i < numSprites; i++) {
SpriteUpdate& update = updates.editItemAt(i);
bool wantSurfaceVisibleAndDrawn = update.state.wantSurfaceVisible()
&& update.state.surfaceDrawn;
bool becomingVisible = wantSurfaceVisibleAndDrawn && !update.state.surfaceVisible;
bool becomingHidden = !wantSurfaceVisibleAndDrawn && update.state.surfaceVisible;
if (update.state.surfaceControl != NULL && (becomingVisible || becomingHidden
|| (wantSurfaceVisibleAndDrawn && (update.state.dirty & (DIRTY_ALPHA
| DIRTY_POSITION | DIRTY_TRANSFORMATION_MATRIX | DIRTY_LAYER
| DIRTY_VISIBILITY | DIRTY_HOTSPOT))))) {
......
}
if (needApplyTransaction) {
status_t status = t.apply();
if (status) {
ALOGE("Error applying Surface transaction");
}
}
......
}
一次的光标的更新就会波及到如此多的代码逻辑,可见UI真是不容易。其余的逻辑线不论,这次咱们只关怀光标的图层。上述代码通过 obtainSurface()
来创立 Surface。
frameworks/base/libs/input/SpriteController.cpp
sp<SurfaceControl> SpriteController::obtainSurface(int32_t width, int32_t height) {
ensureSurfaceComposerClient();
sp<SurfaceControl> surfaceControl = mSurfaceComposerClient->createSurface(
String8("Sprite"), width, height, PIXEL_FORMAT_RGBA_8888,
ISurfaceComposerClient::eHidden |
ISurfaceComposerClient::eCursorWindow);
if (surfaceControl == NULL || !surfaceControl->isValid()) {
ALOGE("Error creating sprite surface.");
return NULL;
}
return surfaceControl;
}
这里咱们须要重点关注的是 createSurface()
办法中的参数 flags
。Sprite 中这个 flags
设置了eHidden
和eCursorWindow
,它们表明创立的 Surface 是暗藏的,并标识为 Cursor 应用。
来到 Surface
Input 中为光标创立了一个 Surface,并且标识这是一个 Cursor 应用的 Surface。之后,Surface 中会依据情景对光标图层做非凡解决,这里的关键字就是 Cursor
。
咱们还是以光标图层为主线进行跟踪,先持续看下createSurface()
。通过一系列的 Binder 调用和 Message传递,最终通过 SurfaceFlinger 的createLayer()
实现图层创立。
frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
status_t SurfaceFlinger::createLayer(const String8& name, const sp<Client>& client, uint32_t w,
uint32_t h, PixelFormat format, uint32_t flags,
int32_t windowType, int32_t ownerUid, sp<IBinder>* handle,
sp<IGraphicBufferProducer>* gbp,
const sp<IBinder>& parentHandle,
const sp<Layer>& parentLayer) {
......
switch (flags & ISurfaceComposerClient::eFXSurfaceMask) {
// 一般图层
case ISurfaceComposerClient::eFXSurfaceNormal:
result = createBufferLayer(client,
uniqueName, w, h, flags, format,
handle, gbp, &layer);
break;
// 纯色图层
case ISurfaceComposerClient::eFXSurfaceColor:
result = createColorLayer(client,
uniqueName, w, h, flags,
handle, &layer);
break;
default:
result = BAD_VALUE;
break;
}
......
// Client中通过Layer治理Surface,将创立的Layer退出到LayerStack中
result = addClientLayer(client, *handle, *gbp, layer, parentHandle, parentLayer);
if (result != NO_ERROR) {
return result;
}
mInterceptor->saveSurfaceCreation(layer);
setTransactionFlags(eTransactionNeeded);
return result;
}
createLayer()
中,光标算是一般图层,所以仅需调用createBufferLayer()
来创立。
frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
status_t SurfaceFlinger::createBufferLayer(const sp<Client>& client,
const String8& name, uint32_t w, uint32_t h, uint32_t flags, PixelFormat& format,
sp<IBinder>* handle, sp<IGraphicBufferProducer>* gbp, sp<Layer>* outLayer)
{
......
// 创立一个BufferLayer
sp<BufferLayer> layer = new BufferLayer(this, client, name, w, h, flags);
// 设置Buffer属性
status_t err = layer->setBuffers(w, h, format, flags);
if (err == NO_ERROR) {
*handle = layer->getHandle(); // 获取Layer的句柄
*gbp = layer->getProducer(); // 获取GraphicBufferProducer对象
*outLayer = layer;
}
ALOGE_IF(err, "createBufferLayer() failed (%s)", strerror(-err));
return err;
}
其中layer->setBuffers()
设置了该BufferLayer的属性。能够看到,当申请的是一个 Cursor 图层时,mPotentialCursor
被设置为true
,表明该 BufferLayer 作为 Cursor 应用。
frameworks/native/services/surfaceflinger/BufferLayer.cpp
status_t BufferLayer::setBuffers(uint32_t w, uint32_t h, PixelFormat format, uint32_t flags) {
......
mFormat = format;
mPotentialCursor = (flags & ISurfaceComposerClient::eCursorWindow) ? true : false;
mProtectedByApp = (flags & ISurfaceComposerClient::eProtectedByApp) ? true : false;
mCurrentOpacity = getOpacityForFormat(format);
mConsumer->setDefaultBufferSize(w, h);
mConsumer->setDefaultBufferFormat(format);
mConsumer->setConsumerUsageBits(getEffectiveUsage(0));
return NO_ERROR;
}
SurfaceFlinger 中的 Cursor 操作
下面讲到 Cursor Layer 最外围的属性mPotentialCursor
,createSurface()
只是设置了这个属性,真正的应用在 SurfaceFlinger 渲染过程中。接着我发现,想把这个货色看明确,先须要把 Android 图形合成弄清楚,这可是的宏大的工程。借张图,有趣味的本人钻研。
然而,工夫无限,怎么办?我的解决办法就是搜寻关键字。搜寻关键字Cursor
后,能够失去一些相干的操作。SurfaceFlinger 接管到 Vsync 信号后,会调用handleMessageRefresh()
来刷新显示。
frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
void SurfaceFlinger::handleMessageRefresh() {
......
preComposition(refreshStartTime); //合成预处理
rebuildLayerStacks(); //从新构建LayerStacks
setUpHWComposer(); //更新HWComposer的图层和属性
doDebugFlashRegions(); //图形绘制的debug模式
doTracing("handleRefresh");
logLayerStats();
doComposition(); //合成所有图层
postComposition(refreshStartTime); //合成后处理
......
}
咱们还是只关怀 Cursor 的操作,它位于 HWComposer 管制的图层中。
frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
void SurfaceFlinger::setUpHWComposer() {
......
// 遍历所有的DisplayDevice,为绘制做筹备
for (size_t dpy=0 ; dpy<mDisplays.size() ; dpy++) {
......
mDisplays[dpy]->beginFrame(mustRecompose);
if (mustRecompose) {
mDisplays[dpy]->lastCompositionHadVisibleLayers = !empty;
}
}
// 设置HWC Layer
if (CC_UNLIKELY(mGeometryInvalid)) {
mGeometryInvalid = false;
for (size_t dpy=0 ; dpy<mDisplays.size() ; dpy++) {
......
for (size_t i = 0; i < currentLayers.size(); i++) {
const auto& layer = currentLayers[i];
// 尝试创立HWC Layer,如果失败则强制OpenGL渲染
if (!layer->hasHwcLayer(hwcId)) {
if (!layer->createHwcLayer(getBE().mHwc.get(), hwcId)) {
layer->forceClientComposition(hwcId);
continue;
}
}
// 设置HWC Layer的显示区域、合成模式、Alpha、Order等
layer->setGeometry(displayDevice, i);
// HWC被禁止或绘制debug模式时,强制OpenGL渲染
if (mDebugDisableHWC || mDebugRegion) {
layer->forceClientComposition(hwcId);
}
......
}
// 筹备HWC须要渲染的数据
for (size_t displayId = 0; displayId < mDisplays.size(); ++displayId) {
auto& displayDevice = mDisplays[displayId];
const auto hwcId = displayDevice->getHwcDisplayId();
......
//调用 setPerFrameData办法
layer->setPerFrameData(displayDevice);
......
}
......
for (size_t displayId = 0; displayId < mDisplays.size(); ++displayId) {
......
// 尝试进行显示
status_t result = displayDevice->prepareFrame(*getBE().mHwc);
......
}
}
其中setPerFrameData()
实现 HWComposer 的相干设置,为显示做筹备。
frameworks/native/services/surfaceflinger/BufferLayer.cpp
void BufferLayer::setPerFrameData(const sp<const DisplayDevice>& displayDevice) {
......
// 设置可见区域
auto error = hwcLayer->setVisibleRegion(visible);
......
// 设置刷新区域
error = hwcLayer->setSurfaceDamage(surfaceDamageRegion);
......
// Sideband layers设置
if (getBE().compositionInfo.hwc.sidebandStream.get()) {
setCompositionType(hwcId, HWC2::Composition::Sideband);
error = hwcLayer->setSidebandStream(getBE().compositionInfo.hwc.sidebandStream->handle());
......
return;
}
if (mPotentialCursor) {
// Cursor layers设置
setCompositionType(hwcId, HWC2::Composition::Cursor);
} else {
// Device layers设置
setCompositionType(hwcId, HWC2::Composition::Device);
}
// 设置色调空间
error = hwcLayer->setDataspace(mCurrentDataSpace);
if (error != HWC2::Error::None) {
ALOGE("[%s] Failed to set dataspace %d: %s (%d)", mName.string(), mCurrentDataSpace,
to_string(error).c_str(), static_cast<int32_t>(error));
}
// 获取HDR数据并设置到HWC中
const HdrMetadata& metadata = mConsumer->getCurrentHdrMetadata();
error = hwcLayer->setPerFrameMetadata(displayDevice->getSupportedPerFrameMetadata(), metadata);
......
// 获取渲染的数据buffer和Fence,设置到HWC中
sp<GraphicBuffer> hwcBuffer;
hwcInfo.bufferCache.getHwcBuffer(getBE().compositionInfo.mBufferSlot,
getBE().compositionInfo.mBuffer, &hwcSlot, &hwcBuffer);
auto acquireFence = mConsumer->getCurrentFence();
error = hwcLayer->setBuffer(hwcSlot, hwcBuffer, acquireFence);
......
}
咱们终于找到了心愿看到的mPotentialCursor
,通过这个标识通知 HWC2 这是一个 CursorLayer。除此之外,对于 CursorLayer 的操作与 DeviceLayer 并没有区别。所以,SurfaceFlinger 更多的是心愿 HWComposer 依据 Layer 的类型进行不同解决。目前 HWC2 反对的 Layer 类型有,
- HWC2_COMPOSITION_CLIENT:不通过 HWC 硬件来合成图层。GPU 将这类图层合成到一个图像 Buffer 中,而后传递给 HWC。
- HWC2_COMPOSITION_DEVICE:应用 HWC 硬件来合成图层。
- HWC2_COMPOSITION_SOLID_COLOR:用来解决 ColorLayer 数据,如果 HWC 不反对,则改为应用 CLIENT 形式合成。
- HWC2_COMPOSITION_CURSOR:用来解决 CursorLayer 数据,地位通过
setCursorPosition
异步设置。如果 HWC 不反对,则改为应用 CLIENT 或 DEVICE 形式合成。 - HWC2_COMPOSITION_SIDEBAND:对于这种 Layer,须要由内部机制提供内容更新,例如电视信号的视频数据。如果 HWC 不反对,则改为应用 CLIENT 或 DEVICE 形式合成,但可能无奈正确显示。
Cursor Layer还有一个重要的操作,setCursorPosition()
,这个办法用来设置 Cursor 的地位,具体的实现仍然在 HWComposer 中。当用户过程更新 Surface 图形时,SurfaceFlinger 会发送INVALIDATE
音讯给相应的 Layer。音讯解决函数调用handleTransaction()
和handlePageFlip()
来更新Layer对象。handleTransaction()
用来解决 Layer 和显示设施的变动,它持续调用handleTransactionLocked()
。
frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
void SurfaceFlinger::handleTransactionLocked(uint32_t transactionFlags)
{
......
// 解决Layer的变动
if (transactionFlags & eTraversalNeeded) {
......
}
// 解决显示设施的变动
if (transactionFlags & eDisplayTransactionNeeded) {
processDisplayChangesLocked();
processDisplayHotplugEventsLocked();
}
// 设置transform hint
if (transactionFlags & (eDisplayLayerStackChanged|eDisplayTransactionNeeded)) {
......
}
//解决Layer的增减
if (mLayersAdded) {
......
}
if (mLayersRemoved) {
......
}
commitTransaction();
// 更新光标地位
updateCursorAsync();
}
咱们找到了 Cursor 更新的中央,SurfaceFlinger 更新图形时会同步更新光标地位。之后,在 Vsync 到来时,实现图像的更新显示。
frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
void SurfaceFlinger::updateCursorAsync()
{
for (size_t displayId = 0; displayId < mDisplays.size(); ++displayId) {
......
// 调用Layer的对应办法
for (auto& layer : displayDevice->getVisibleLayersSortedByZ()) {
layer->updateCursorPosition(displayDevice);
}
}
}
frameworks/native/services/surfaceflinger/Layer.cpp
void Layer::updateCursorPosition(const sp<const DisplayDevice>& displayDevice) {
// HWC Layer不存在或者不是Cursor Layer,不做解决
auto hwcId = displayDevice->getHwcDisplayId();
if (getBE().mHwcLayers.count(hwcId) == 0 ||
getCompositionType(hwcId) != HWC2::Composition::Cursor) {
return;
}
......
// 获取图层的地位
Rect bounds = reduce(win, s.activeTransparentRegion);
Rect frame(getTransform().transform(bounds));
frame.intersect(displayDevice->getViewport(), &frame);
if (!s.finalCrop.isEmpty()) {
frame.intersect(s.finalCrop, &frame);
}
auto& displayTransform(displayDevice->getTransform());
auto position = displayTransform.transform(frame);
// 调用HWC的办法来设置图层地位
auto error = getBE().mHwcLayers[hwcId].layer->setCursorPosition(position.left, position.top);
}
达到 HWComposer
下面剖析了许多代码,但真正与 Cursor 相干的并不多。CursorLayer 的真正实现还是在 HWComposer 中。然而 HWComposer 的实现是与平台相干的,不同的平台对 CursorLayer 的实现可能不同。效率的形式是应用一个独立的硬件 OSD 来显示 CursorLayer,而后通过硬件合成的形式将 CursorLayer 叠加到 UI 显示层。应用这种形式,光标的挪动效率也很高,只有扭转硬件 OSD 显示的地位即可。如果没有独立的硬件 OSD 来应用,就只能在规范显示层上进行软件叠加,或者应用 GPU 来叠加。
因为跟平台相干的实现具备私密性,这里不再持续剖析。
参考文档:
Android GUI零碎之SurfaceFlinger)
Android SurfaceFlinger学习-HWComposer Composition工作流程
挪动端显示技术杂谈