namespace android {
    class Functor {
    public:
    Functor() {}
    virtual ~Functor() {}
    virtual int operator()(int /*what*/, void * /*data*/) { return 0; }
    };
}

namespace android {
namespace uirenderer {
/**
* Structure used by OpenGLRenderer::callDrawGLFunction() to pass and
* receive data from OpenGL functors.
*/
struct DrawGlInfo {
// Input: current clip rect
int clipLeft;
int clipTop;
int clipRight;
int clipBottom;
// Input: current width/height of destination surface
int width;
int height;
// Input: is the render target an FBO
bool isLayer;
// Input: current transform matrix, in OpenGL format
float transform[16];
// Input: Color space.
// const SkColorSpace* color_space_ptr;
const void* color_space_ptr;
// Output: dirty region to redraw
float dirtyLeft;
float dirtyTop;
float dirtyRight;
float dirtyBottom;
/**
* Values used as the "what" parameter of the functor.
*/
enum Mode {
// Indicates that the functor is called to perform a draw
kModeDraw,
// Indicates the the functor is called only to perform
// processing and that no draw should be attempted
kModeProcess,
// Same as kModeProcess, however there is no GL context because it was
// lost or destroyed
kModeProcessNoContext,
// Invoked every time the UI thread pushes over a frame to the render thread
// *and the owning view has a dirty display list*. This is a signal to sync
// any data that needs to be shared between the UI thread and the render thread.
// During this time the UI thread is blocked.
kModeSync
};
/**
* Values used by OpenGL functors to tell the framework
* what to do next.
*/
enum Status {
// The functor is done
kStatusDone = 0x0,
// DisplayList actually issued GL drawing commands.
// This is used to signal the HardwareRenderer that the
// buffers should be flipped - otherwise, there were no
// changes to the buffer, so no need to flip. Some hardware
// has issues with stale buffer contents when no GL
// commands are issued.
kStatusDrew = 0x4
};
}; // struct DrawGlInfo
} // namespace uirenderer
} // namespace android

// MyFunctor定義
namespace android {
class MyFunctor : Functor {
public:
MyFunctor();
virtual ~MyFunctor() {}
virtual void onExec(int what,
android::uirenderer::DrawGlInfo* info);
virtual std::string getFunctorName() = 0;
int operator()(int /*what*/, void * /*data*/) override;
private:

};

}
// MyFunctor實現
int MyFunctor::operator() (int what, void *data) {
if (what == android::uirenderer::DrawGlInfo::Mode::kModeDraw) {
auto info = (android::uirenderer::DrawGlInfo*)data;
onExec(what, info);
}
return android::uirenderer::DrawGlInfo::Status::kStatusDone;

}
void MyFunctor::onExec(int what, android::uirenderer::DrawGlInfo* info) {
// 渲染實現

}

// java MyFunctor定義
class MyFunctor {
private long nativeHandle;
public MyFunctor() {
nativeHandle = createNativeHandle();

}
public long getNativeHandle() {
return nativeHanlde;

}
private native long createNativeHandle();

}
// jni 方法：
extern "C" JNIEXPORT jlong JNICALL
Java_com_test_MyFunctor_createNativeHandle(JNIEnv *env, jobject thiz) {
auto p = new MyFunctor();
return (jlong)p;
}

public class FunctorView extends View {
...
private static Method sDrawGLFunction;
private MyFunctor myFunctor = new MyFunctor();
@Override
public void onDraw(Canvas cvs) {
super.onDraw(cvs);
getDrawFunctorMethodIfNot();
invokeFunctor(cvs, myFunctor);
}
private void invokeFunctor(Canvas canvas, MyFunctor functor) {
if (functor.getNativeHandle() != 0 && sDrawGLFunction != null) {
try {
sDrawGLFunction.invoke(canvas, functor.getNativeHandle());
} catch (Throwable t) {
// log
}
}
}
public synchronized static Method getDrawFunctorMethodIfNot() {

if (sDrawGLFunction != null) {
return sDrawGLFunction;

}
hasReflect = true;
String className;
String methodName;
Class<?> paramClass = long.class;
try {
if (Build.VERSION.SDK_INT > Build.VERSION_CODES.P) {
className = "android.graphics.RecordingCanvas";
methodName = "callDrawGLFunction2";
} else if (Build.VERSION.SDK_INT > Build.VERSION_CODES.LOLLIPOP_MR1) {
className = "android.view.DisplayListCanvas";
methodName = "callDrawGLFunction2";
} else if (Build.VERSION.SDK_INT == Build.VERSION_CODES.LOLLIPOP) {
className = "android.view.HardwareCanvas";
methodName = "callDrawGLFunction";
} else if (Build.VERSION.SDK_INT == Build.VERSION_CODES.LOLLIPOP_MR1) {
className = "android.view.HardwareCanvas";
methodName = "callDrawGLFunction2";
} else {
className = "android.view.HardwareCanvas";
methodName = "callDrawGLFunction";
paramClass = int.class;
}
Class<?> canvasClazz = Class.forName(className);
sDrawGLFunction = SystemApiReflector.getInstance().
getDeclaredMethod(SystemApiReflector.KEY_GL_FUNCTOR, canvasClazz,
methodName, paramClass);
} catch (Throwable t) {
// 異常
}
if (sDrawGLFunction != null) {
sDrawGLFunction.setAccessible(true);
} else {
// （異常)
}
return sDrawGLFunction;
}
}

// Android 9.0 code
// 保存狀態
void RenderState::interruptForFunctorInvoke() {
mCaches->setProgram(nullptr);
mCaches->textureState().resetActiveTexture();
meshState().unbindMeshBuffer();

meshState().unbindIndicesBuffer();
meshState().resetVertexPointers();
meshState().disableTexCoordsVertexArray();
debugOverdraw(false, false);
// TODO: We need a way to know whether the functor is sRGB aware (b/32072673)
if (mCaches->extensions().hasLinearBlending() &&
mCaches->extensions().hasSRGBWriteControl()) {
glDisable(GL_FRAMEBUFFER_SRGB_EXT);
}
}
// 恢復狀態
void RenderState::resumeFromFunctorInvoke() {
if (mCaches->extensions().hasLinearBlending() &&
mCaches->extensions().hasSRGBWriteControl()) {
glEnable(GL_FRAMEBUFFER_SRGB_EXT);

}
glViewport(0, 0, mViewportWidth, mViewportHeight);
glBindFramebuffer(GL_FRAMEBUFFER, mFramebuffer);
debugOverdraw(false, false);
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
scissor().invalidate();
blend().invalidate();
mCaches->textureState().activateTexture(0);
mCaches->textureState().resetBoundTextures();
}

activity.getApplicationContext().registerComponentCallbacks(
new ComponentCallbacks2() {
@Override
public void onTrimMemory(int level) {
if (level == 15) {
// 觸發functor重建
}
}
@Override
public void onConfigurationChanged(Configuration newConfig) {
}
@Override
public void onLowMemory() {
}
});