/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.gecko.gfx;

import org.mozilla.gecko.AppConstants;
import org.mozilla.gecko.GeckoAppShell;
import org.mozilla.gecko.R;
import org.mozilla.gecko.Tab;
import org.mozilla.gecko.Tabs;
import org.mozilla.gecko.gfx.Layer.RenderContext;
import org.mozilla.gecko.mozglue.DirectBufferAllocator;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.graphics.Rect;
import android.graphics.RectF;
import android.opengl.GLES20;
import android.os.SystemClock;
import android.util.Log;

import org.mozilla.gecko.annotation.WrapForJNI;
import org.mozilla.gecko.util.ThreadUtils;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.ArrayList;
import java.util.List;

import javax.microedition.khronos.egl.EGLConfig;

/**
 * The layer renderer implements the rendering logic for a layer view.
 */
public class LayerRenderer implements Tabs.OnTabsChangedListener {
    private static final String LOGTAG = "GeckoLayerRenderer";
    private static final String PROFTAG = "GeckoLayerRendererProf";

    /*
     * The amount of time a frame is allowed to take to render before we declare it a dropped
     * frame.
     */
    private static final int MAX_FRAME_TIME = 16;   /* 1000 ms / 60 FPS */

    private static final int FRAME_RATE_METER_WIDTH = 128;
    private static final int FRAME_RATE_METER_HEIGHT = 32;

    private static final long NANOS_PER_MS = 1000000;
    private static final int NANOS_PER_SECOND = 1000000000;

    private static final int MAX_SCROLL_SPEED_TO_REQUEST_ZOOM_RENDER = 5;

    private final LayerView mView;
    private final ScrollbarLayer mHorizScrollLayer;
    private final ScrollbarLayer mVertScrollLayer;
    private final FadeRunnable mFadeRunnable;
    private ByteBuffer mCoordByteBuffer;
    private FloatBuffer mCoordBuffer;
    private RenderContext mLastPageContext;
    private int mMaxTextureSize;
    private int mBackgroundColor;

    private long mLastFrameTime;
    private final CopyOnWriteArrayList<RenderTask> mTasks;

    private final CopyOnWriteArrayList<Layer> mExtraLayers = new CopyOnWriteArrayList<Layer>();

    // Dropped frames display
    private final int[] mFrameTimings;
    private int mCurrentFrame, mFrameTimingsSum, mDroppedFrames;

    // Render profiling output
    private int mFramesRendered;
    private float mCompleteFramesRendered;
    private boolean mProfileRender;
    private long mProfileOutputTime;

    private IntBuffer mPixelBuffer;

    // Used by GLES 2.0
    private int mProgram;
    private int mPositionHandle;
    private int mTextureHandle;
    private int mSampleHandle;
    private int mTMatrixHandle;

    private List<LayerView.ZoomedViewListener> mZoomedViewListeners;
    private float mLastViewLeft;
    private float mLastViewTop;

    // column-major matrix applied to each vertex to shift the viewport from
    // one ranging from (-1, -1),(1,1) to (0,0),(1,1) and to scale all sizes by
    // a factor of 2 to fill up the screen
    public static final float[] DEFAULT_TEXTURE_MATRIX = {
        2.0f, 0.0f, 0.0f, 0.0f,
        0.0f, 2.0f, 0.0f, 0.0f,
        0.0f, 0.0f, 2.0f, 0.0f,
        -1.0f, -1.0f, 0.0f, 1.0f
    };

    private static final int COORD_BUFFER_SIZE = 20;

    // The shaders run on the GPU directly, the vertex shader is only applying the
    // matrix transform detailed above

    // Note we flip the y-coordinate in the vertex shader from a
    // coordinate system with (0,0) in the top left to one with (0,0) in
    // the bottom left.

    public static final String DEFAULT_VERTEX_SHADER =
        "uniform mat4 uTMatrix;\n" +
        "attribute vec4 vPosition;\n" +
        "attribute vec2 aTexCoord;\n" +
        "varying vec2 vTexCoord;\n" +
        "void main() {\n" +
        "    gl_Position = uTMatrix * vPosition;\n" +
        "    vTexCoord.x = aTexCoord.x;\n" +
        "    vTexCoord.y = 1.0 - aTexCoord.y;\n" +
        "}\n";

    // We use highp because the screenshot textures
    // we use are large and we stretch them alot
    // so we need all the precision we can get.
    // Unfortunately, highp is not required by ES 2.0
    // so on GPU's like Mali we end up getting mediump
    public static final String DEFAULT_FRAGMENT_SHADER =
        "precision highp float;\n" +
        "varying vec2 vTexCoord;\n" +
        "uniform sampler2D sTexture;\n" +
        "void main() {\n" +
        "    gl_FragColor = texture2D(sTexture, vTexCoord);\n" +
        "}\n";

    public LayerRenderer(LayerView view) {
        mView = view;

        final BitmapFactory.Options bitmapOptions = new BitmapFactory.Options();
        bitmapOptions.inScaled = false;
        Bitmap scrollbarImage =
                BitmapUtils.decodeResource(view.getContext(), R.drawable.scrollbar, bitmapOptions);
        IntSize size = new IntSize(scrollbarImage.getWidth(), scrollbarImage.getHeight());
        scrollbarImage = expandCanvasToPowerOfTwo(scrollbarImage, size);

        mTasks = new CopyOnWriteArrayList<RenderTask>();
        mLastFrameTime = System.nanoTime();

        if (!AppConstants.MOZ_ANDROID_APZ) {
            mVertScrollLayer = new ScrollbarLayer(this, scrollbarImage, size, true);
            mHorizScrollLayer = new ScrollbarLayer(this, diagonalFlip(scrollbarImage), new IntSize(size.height, size.width), false);
            mFadeRunnable = new FadeRunnable();
        } else {
            // final variables need to be initialized in the constructor
            mVertScrollLayer = null;
            mHorizScrollLayer = null;
            mFadeRunnable = null;
        }

        mFrameTimings = new int[60];
        mCurrentFrame = mFrameTimingsSum = mDroppedFrames = 0;

        Tabs.registerOnTabsChangedListener(this);
        mZoomedViewListeners = new ArrayList<LayerView.ZoomedViewListener>();
    }

    private Bitmap expandCanvasToPowerOfTwo(Bitmap image, IntSize size) {
        IntSize potSize = size.nextPowerOfTwo();
        if (size.equals(potSize)) {
            return image;
        }
        // make the bitmap size a power-of-two in both dimensions if it's not already.
        Bitmap potImage = Bitmap.createBitmap(potSize.width, potSize.height, image.getConfig());
        new Canvas(potImage).drawBitmap(image, new Matrix(), null);
        return potImage;
    }

    private Bitmap diagonalFlip(Bitmap image) {
        Matrix rotation = new Matrix();
        rotation.setValues(new float[] { 0, 1, 0, 1, 0, 0, 0, 0, 1 }); // transform (x,y) into (y,x)
        Bitmap rotated = Bitmap.createBitmap(image, 0, 0, image.getWidth(), image.getHeight(), rotation, true);
        return rotated;
    }

    public void destroy() {
        if (mCoordByteBuffer != null) {
            DirectBufferAllocator.free(mCoordByteBuffer);
            mCoordByteBuffer = null;
            mCoordBuffer = null;
        }
        if (!AppConstants.MOZ_ANDROID_APZ) {
            mHorizScrollLayer.destroy();
            mVertScrollLayer.destroy();
        }
        Tabs.unregisterOnTabsChangedListener(this);
        mZoomedViewListeners.clear();
    }

    void onSurfaceCreated(EGLConfig config) {
        checkMonitoringEnabled();
        createDefaultProgram();
        activateDefaultProgram();
    }

    public void createDefaultProgram() {
        int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, DEFAULT_VERTEX_SHADER);
        int fragmentShader = loadShader(GLES20.GL_FRAGMENT_SHADER, DEFAULT_FRAGMENT_SHADER);

        mProgram = GLES20.glCreateProgram();
        GLES20.glAttachShader(mProgram, vertexShader);   // add the vertex shader to program
        GLES20.glAttachShader(mProgram, fragmentShader); // add the fragment shader to program
        GLES20.glLinkProgram(mProgram);                  // creates OpenGL program executables

        // Get handles to the vertex shader's vPosition, aTexCoord, sTexture, and uTMatrix members.
        mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");
        mTextureHandle = GLES20.glGetAttribLocation(mProgram, "aTexCoord");
        mSampleHandle = GLES20.glGetUniformLocation(mProgram, "sTexture");
        mTMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uTMatrix");

        int maxTextureSizeResult[] = new int[1];
        GLES20.glGetIntegerv(GLES20.GL_MAX_TEXTURE_SIZE, maxTextureSizeResult, 0);
        mMaxTextureSize = maxTextureSizeResult[0];
    }

    // Activates the shader program.
    public void activateDefaultProgram() {
        // Add the program to the OpenGL environment
        GLES20.glUseProgram(mProgram);

        // Set the transformation matrix
        GLES20.glUniformMatrix4fv(mTMatrixHandle, 1, false, DEFAULT_TEXTURE_MATRIX, 0);

        // Enable the arrays from which we get the vertex and texture coordinates
        GLES20.glEnableVertexAttribArray(mPositionHandle);
        GLES20.glEnableVertexAttribArray(mTextureHandle);

        GLES20.glUniform1i(mSampleHandle, 0);

        // TODO: Move these calls into a separate deactivate() call that is called after the
        // underlay and overlay are rendered.
    }

    // Deactivates the shader program. This must be done to avoid crashes after returning to the
    // Gecko C++ compositor from Java.
    public void deactivateDefaultProgram() {
        GLES20.glDisableVertexAttribArray(mTextureHandle);
        GLES20.glDisableVertexAttribArray(mPositionHandle);
        GLES20.glUseProgram(0);
    }

    void restoreState(boolean enableScissor, int scissorX, int scissorY, int scissorW, int scissorH) {
        GLES20.glScissor(scissorX, scissorY, scissorW, scissorH);
        if (enableScissor) {
            GLES20.glEnable(GLES20.GL_SCISSOR_TEST);
        } else {
            GLES20.glDisable(GLES20.GL_SCISSOR_TEST);
        }
    }

    public int getMaxTextureSize() {
        return mMaxTextureSize;
    }

    public void postRenderTask(RenderTask aTask) {
        mTasks.add(aTask);
        mView.requestRender();
    }

    public void removeRenderTask(RenderTask aTask) {
        mTasks.remove(aTask);
    }

    private void runRenderTasks(CopyOnWriteArrayList<RenderTask> tasks, boolean after, long frameStartTime) {
        for (RenderTask task : tasks) {
            if (task.runAfter != after) {
                continue;
            }

            boolean stillRunning = task.run(frameStartTime - mLastFrameTime, frameStartTime);

            // Remove the task from the list if its finished
            if (!stillRunning) {
                tasks.remove(task);
            }
        }
    }

    public void addLayer(Layer layer) {
        synchronized (mExtraLayers) {
            if (mExtraLayers.contains(layer)) {
                mExtraLayers.remove(layer);
            }

            mExtraLayers.add(layer);
        }
    }

    public void removeLayer(Layer layer) {
        synchronized (mExtraLayers) {
            mExtraLayers.remove(layer);
        }
    }

    private void printCheckerboardStats() {
        Log.d(PROFTAG, "Frames rendered over last 1000ms: " + mCompleteFramesRendered + "/" + mFramesRendered);
        mFramesRendered = 0;
        mCompleteFramesRendered = 0;
    }

    /** Used by robocop for testing purposes. Not for production use! */
    IntBuffer getPixels() {
        IntBuffer pixelBuffer = IntBuffer.allocate(mView.getWidth() * mView.getHeight());
        synchronized (pixelBuffer) {
            mPixelBuffer = pixelBuffer;
            mView.requestRender();
            try {
                pixelBuffer.wait();
            } catch (InterruptedException ie) {
            }
            mPixelBuffer = null;
        }
        return pixelBuffer;
    }

    private RenderContext createScreenContext(ImmutableViewportMetrics metrics) {
        RectF viewport = new RectF(0.0f, 0.0f, metrics.getWidth(), metrics.getHeight());
        RectF pageRect = metrics.getPageRect();

        return createContext(viewport, pageRect, 1.0f);
    }

    private RenderContext createPageContext(ImmutableViewportMetrics metrics) {
        RectF viewport = metrics.getViewport();
        RectF pageRect = metrics.getPageRect();
        float zoomFactor = metrics.zoomFactor;

        return createContext(new RectF(RectUtils.round(viewport)), pageRect, zoomFactor);
    }

    private RenderContext createContext(RectF viewport, RectF pageRect, float zoomFactor) {
        if (mCoordBuffer == null) {
            // Initialize the FloatBuffer that will be used to store all vertices and texture
            // coordinates in draw() commands.
            mCoordByteBuffer = DirectBufferAllocator.allocate(COORD_BUFFER_SIZE * 4);
            mCoordByteBuffer.order(ByteOrder.nativeOrder());
            mCoordBuffer = mCoordByteBuffer.asFloatBuffer();
            if (mCoordBuffer == null) {
                throw new IllegalStateException();
            }
        }
        return new RenderContext(viewport, pageRect, zoomFactor,
                                 mPositionHandle, mTextureHandle, mCoordBuffer);
    }

    private void updateDroppedFrames(long frameStartTime) {
        int frameElapsedTime = (int)((System.nanoTime() - frameStartTime) / NANOS_PER_MS);

        /* Update the running statistics. */
        mFrameTimingsSum -= mFrameTimings[mCurrentFrame];
        mFrameTimingsSum += frameElapsedTime;
        mDroppedFrames -= (mFrameTimings[mCurrentFrame] + 1) / MAX_FRAME_TIME;
        mDroppedFrames += (frameElapsedTime + 1) / MAX_FRAME_TIME;

        mFrameTimings[mCurrentFrame] = frameElapsedTime;
        mCurrentFrame = (mCurrentFrame + 1) % mFrameTimings.length;

        int averageTime = mFrameTimingsSum / mFrameTimings.length;
    }

    void checkMonitoringEnabled() {
        mProfileRender = Log.isLoggable(PROFTAG, Log.DEBUG);
    }

    /*
     * create a vertex shader type (GLES20.GL_VERTEX_SHADER)
     * or a fragment shader type (GLES20.GL_FRAGMENT_SHADER)
     */
    public static int loadShader(int type, String shaderCode) {
        int shader = GLES20.glCreateShader(type);
        GLES20.glShaderSource(shader, shaderCode);
        GLES20.glCompileShader(shader);
        return shader;
    }

    public Frame createFrame(ImmutableViewportMetrics metrics) {
        return new Frame(metrics);
    }

    class FadeRunnable implements Runnable {
        private boolean mStarted;
        long mRunAt; // Would be private but we need both file access and high performance.

        void scheduleStartFade(long delay) {
            mRunAt = SystemClock.elapsedRealtime() + delay;
            if (!mStarted) {
                mView.postDelayed(this, delay);
                mStarted = true;
            }
        }

        void scheduleNextFadeFrame() {
            if (mStarted) {
                Log.e(LOGTAG, "scheduleNextFadeFrame() called while scheduled for starting fade");
            }
            mView.postDelayed(this, 1000L / 60L); // request another frame at 60fps
        }

        boolean timeToFade() {
            return !mStarted;
        }

        @Override
        public void run() {
            long timeDelta = mRunAt - SystemClock.elapsedRealtime();
            if (timeDelta > 0) {
                // the run-at time was pushed back, so reschedule
                mView.postDelayed(this, timeDelta);
            } else {
                // reached the run-at time, execute
                mStarted = false;
                mView.requestRender();
            }
        }
    }

    public class Frame {
        // The timestamp recording the start of this frame.
        private long mFrameStartTime;
        // A fixed snapshot of the viewport metrics that this frame is using to render content.
        private final ImmutableViewportMetrics mFrameMetrics;
        // A rendering context for page-positioned layers, and one for screen-positioned layers.
        private final RenderContext mPageContext, mScreenContext;
        // Whether a layer was updated.
        private boolean mUpdated;
        private final Rect mPageRect;
        private final Rect mAbsolutePageRect;

        public Frame(ImmutableViewportMetrics metrics) {
            mFrameMetrics = metrics;

            // Work out the offset due to margins
            Layer rootLayer = mView.getLayerClient().getRoot();
            mPageContext = createPageContext(metrics);
            mScreenContext = createScreenContext(metrics);

            RectF pageRect = mFrameMetrics.getPageRect();
            mAbsolutePageRect = RectUtils.round(pageRect);

            PointF origin = mFrameMetrics.getOrigin();
            pageRect.offset(-origin.x, -origin.y);
            mPageRect = RectUtils.round(pageRect);
        }

        /** This function is invoked via JNI; be careful when modifying signature. */
        @WrapForJNI(allowMultithread = true)
        public void beginDrawing() {
            mFrameStartTime = System.nanoTime();

            TextureReaper.get().reap();
            TextureGenerator.get().fill();

            mUpdated = true;

            Layer rootLayer = mView.getLayerClient().getRoot();

            // Run through pre-render tasks
            runRenderTasks(mTasks, false, mFrameStartTime);

            if (!AppConstants.MOZ_ANDROID_APZ) {
                boolean hideScrollbars = (mView.getFullScreenState() == FullScreenState.NON_ROOT_ELEMENT);
                if (!mPageContext.fuzzyEquals(mLastPageContext) && !hideScrollbars) {
                    // The viewport or page changed, so show the scrollbars again
                    // as per UX decision. Don't do this if we're disabling scrolling due to
                    // full-screen mode though.
                    mVertScrollLayer.unfade();
                    mHorizScrollLayer.unfade();
                    mFadeRunnable.scheduleStartFade(ScrollbarLayer.FADE_DELAY);
                } else if (mFadeRunnable.timeToFade()) {
                    final long currentMillis = SystemClock.elapsedRealtime();
                    final boolean stillFading = mVertScrollLayer.fade(mFadeRunnable.mRunAt, currentMillis) |
                            mHorizScrollLayer.fade(mFadeRunnable.mRunAt, currentMillis);
                    if (stillFading) {
                        mFadeRunnable.scheduleNextFadeFrame();
                    }
                }
                mLastPageContext = mPageContext;
                mUpdated &= mVertScrollLayer.update(mPageContext);  // called on compositor thread
                mUpdated &= mHorizScrollLayer.update(mPageContext); // called on compositor thread
            }

            /* Update layers. */
            if (rootLayer != null) {
                // Called on compositor thread.
                mUpdated &= rootLayer.update(mPageContext);
            }

            for (Layer layer : mExtraLayers) {
                mUpdated &= layer.update(mPageContext); // called on compositor thread
            }
        }

        private void clear(int color) {
            GLES20.glClearColor(((color >> 16) & 0xFF) / 255.0f,
                                ((color >> 8) & 0xFF) / 255.0f,
                                (color & 0xFF) / 255.0f,
                                0.0f);
            // The bits set here need to match up with those used
            // in gfx/layers/opengl/LayerManagerOGL.cpp.
            GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT |
                           GLES20.GL_DEPTH_BUFFER_BIT);
        }

        /** This function is invoked via JNI; be careful when modifying signature. */
        @WrapForJNI(allowMultithread = true)
        public void drawBackground() {
            // Any GL state which is changed here must be restored in
            // restoreState(...)

            GLES20.glDisable(GLES20.GL_SCISSOR_TEST);

            // Update background color.
            mBackgroundColor = mView.getBackgroundColor();

            // Clear the page area to the page background colour.
            clear(mBackgroundColor);
        }

        @WrapForJNI(allowMultithread = true)
        public void drawForeground() {
            // Any GL state which is changed here must be restored in
            // restoreState(...)

            /* Draw any extra layers that were added (likely plugins) */
            if (mExtraLayers.size() > 0) {
                for (Layer layer : mExtraLayers) {
                    layer.draw(mPageContext);
                }
            }

            if (!AppConstants.MOZ_ANDROID_APZ) {
                /* Draw the vertical scrollbar. */
                if (mPageRect.height() > mFrameMetrics.getHeight())
                    mVertScrollLayer.draw(mPageContext);

                /* Draw the horizontal scrollbar. */
                if (mPageRect.width() > mFrameMetrics.getWidth())
                    mHorizScrollLayer.draw(mPageContext);
            }

            /* Measure how much of the screen is checkerboarding */
            Layer rootLayer = mView.getLayerClient().getRoot();
            if ((rootLayer != null) &&
                (mProfileRender || PanningPerfAPI.isRecordingCheckerboard())) {
                // Calculate the incompletely rendered area of the page
                float checkerboard =  1.0f - GeckoAppShell.computeRenderIntegrity();

                PanningPerfAPI.recordCheckerboard(checkerboard);
                if (checkerboard < 0.0f || checkerboard > 1.0f) {
                    Log.e(LOGTAG, "Checkerboard value out of bounds: " + checkerboard);
                }

                mCompleteFramesRendered += 1.0f - checkerboard;
                mFramesRendered ++;

                if (mFrameStartTime - mProfileOutputTime > NANOS_PER_SECOND) {
                    mProfileOutputTime = mFrameStartTime;
                    printCheckerboardStats();
                }
            }

            runRenderTasks(mTasks, true, mFrameStartTime);

        }

        private void maybeRequestZoomedViewRender(RenderContext context) {
            // Concurrently update of mZoomedViewListeners should not be an issue here
            // because the following line is just a short-circuit
            if (mZoomedViewListeners.size() == 0) {
                return;
            }

            // When scrolling fast, do not request zoomed view render to avoid to slow down
            // the scroll in the main view.
            // Speed is estimated using the offset changes between 2 display frame calls
            final float viewLeft = context.viewport.left;
            final float viewTop = context.viewport.top;
            boolean shouldWaitToRender = false;

            if (Math.abs(mLastViewLeft - viewLeft) > MAX_SCROLL_SPEED_TO_REQUEST_ZOOM_RENDER ||
                Math.abs(mLastViewTop - viewTop) > MAX_SCROLL_SPEED_TO_REQUEST_ZOOM_RENDER) {
                shouldWaitToRender = true;
            }

            mLastViewLeft = viewLeft;
            mLastViewTop = viewTop;

            if (shouldWaitToRender) {
                return;
            }

            ThreadUtils.postToUiThread(new Runnable() {
                @Override
                public void run() {
                    for (LayerView.ZoomedViewListener listener : mZoomedViewListeners) {
                        listener.requestZoomedViewRender();
                    }
                }
            });
        }

        /** This function is invoked via JNI; be careful when modifying signature. */
        @WrapForJNI(allowMultithread = true)
        public void endDrawing() {
            // If a layer update requires further work, schedule another redraw
            if (!mUpdated)
                mView.requestRender();

            PanningPerfAPI.recordFrameTime();

            maybeRequestZoomedViewRender(mPageContext);

            /* Used by robocop for testing purposes */
            IntBuffer pixelBuffer = mPixelBuffer;
            if (mUpdated && pixelBuffer != null) {
                synchronized (pixelBuffer) {
                    pixelBuffer.position(0);
                    GLES20.glReadPixels(0, 0, (int)mScreenContext.viewport.width(),
                                        (int)mScreenContext.viewport.height(), GLES20.GL_RGBA,
                                        GLES20.GL_UNSIGNED_BYTE, pixelBuffer);
                    pixelBuffer.notify();
                }
            }

            // Remove background color once we've painted. GeckoLayerClient is
            // responsible for setting this flag before current document is
            // composited.
            if (mView.getPaintState() == LayerView.PAINT_BEFORE_FIRST) {
                mView.post(new Runnable() {
                    @Override
                    public void run() {
                        mView.setSurfaceBackgroundColor(Color.TRANSPARENT);
                    }
                });
                mView.setPaintState(LayerView.PAINT_AFTER_FIRST);
            }
            mLastFrameTime = mFrameStartTime;
        }
    }

    @Override
    public void onTabChanged(final Tab tab, Tabs.TabEvents msg, String data) {
        // Sets the background of the newly selected tab. This background color
        // gets cleared in endDrawing(). This function runs on the UI thread,
        // but other code that touches the paint state is run on the compositor
        // thread, so this may need to be changed if any problems appear.
        if (msg == Tabs.TabEvents.SELECTED) {
            if (mView != null) {
                mView.setSurfaceBackgroundColor(tab.getBackgroundColor());
                mView.setPaintState(LayerView.PAINT_START);
            }
        }
    }

    public void updateZoomedView(final ByteBuffer data) {
        ThreadUtils.postToUiThread(new Runnable() {
            @Override
            public void run() {
                for (LayerView.ZoomedViewListener listener : mZoomedViewListeners) {
                    data.position(0);
                    listener.updateView(data);
                }
            }
        });
    }

    public void addZoomedViewListener(LayerView.ZoomedViewListener listener) {
        ThreadUtils.assertOnUiThread();
        mZoomedViewListeners.add(listener);
    }

    public void removeZoomedViewListener(LayerView.ZoomedViewListener listener) {
        ThreadUtils.assertOnUiThread();
        mZoomedViewListeners.remove(listener);
    }
}
