lunarview.java

android 例子中的LunarLander。很有代表意义

                            || keyCode == KeyEvent.KEYCODE_SPACE) {
                        setFiring(false);
                        handled = true;
                    } else if (keyCode == KeyEvent.KEYCODE_DPAD_LEFT
                            || keyCode == KeyEvent.KEYCODE_Q
                            || keyCode == KeyEvent.KEYCODE_DPAD_RIGHT
                            || keyCode == KeyEvent.KEYCODE_W) {
                        mRotating = 0;
                        handled = true;
                    }
                }
            }

            return handled;
        }

        /**
         * Draws the ship, fuel/speed bars, and background to the provided
         * Canvas.
         */
        private void doDraw(Canvas canvas) {
            // Draw the background image. Operations on the Canvas accumulate
            // so this is like clearing the screen.
            canvas.drawBitmap(mBackgroundImage, 0, 0, null);

            int yTop = mCanvasHeight - ((int) mY + mLanderHeight / 2);
            int xLeft = (int) mX - mLanderWidth / 2;

            // Draw the fuel gauge
            int fuelWidth = (int) (UI_BAR * mFuel / PHYS_FUEL_MAX);
            mScratchRect.set(4, 4, 4 + fuelWidth, 4 + UI_BAR_HEIGHT);
            canvas.drawRect(mScratchRect, mLinePaint);

            // Draw the speed gauge, with a two-tone effect
            double speed = Math.sqrt(mDX * mDX + mDY * mDY);
            int speedWidth = (int) (UI_BAR * speed / PHYS_SPEED_MAX);

            if (speed <= mGoalSpeed) {
                mScratchRect.set(4 + UI_BAR + 4, 4,
                        4 + UI_BAR + 4 + speedWidth, 4 + UI_BAR_HEIGHT);
                canvas.drawRect(mScratchRect, mLinePaint);
            } else {
                // Draw the bad color in back, with the good color in front of
                // it
                mScratchRect.set(4 + UI_BAR + 4, 4,
                        4 + UI_BAR + 4 + speedWidth, 4 + UI_BAR_HEIGHT);
                canvas.drawRect(mScratchRect, mLinePaintBad);
                int goalWidth = (UI_BAR * mGoalSpeed / PHYS_SPEED_MAX);
                mScratchRect.set(4 + UI_BAR + 4, 4, 4 + UI_BAR + 4 + goalWidth,
                        4 + UI_BAR_HEIGHT);
                canvas.drawRect(mScratchRect, mLinePaint);
            }

            // Draw the landing pad
            canvas.drawLine(mGoalX, 1 + mCanvasHeight - TARGET_PAD_HEIGHT,
                    mGoalX + mGoalWidth, 1 + mCanvasHeight - TARGET_PAD_HEIGHT,
                    mLinePaint);


            // Draw the ship with its current rotation
            canvas.save();
            canvas.rotate((float) mHeading, (float) mX, mCanvasHeight
                    - (float) mY);
            if (mMode == STATE_LOSE) {
                mCrashedImage.setBounds(xLeft, yTop, xLeft + mLanderWidth, yTop
                        + mLanderHeight);
                mCrashedImage.draw(canvas);
            } else if (mEngineFiring) {
                mFiringImage.setBounds(xLeft, yTop, xLeft + mLanderWidth, yTop
                        + mLanderHeight);
                mFiringImage.draw(canvas);
            } else {
                mLanderImage.setBounds(xLeft, yTop, xLeft + mLanderWidth, yTop
                        + mLanderHeight);
                mLanderImage.draw(canvas);
            }
            canvas.restore();
        }

        /**
         * Figures the lander state (x, y, fuel, ...) based on the passage of
         * realtime. Does not invalidate(). Called at the start of draw().
         * Detects the end-of-game and sets the UI to the next state.
         */
        private void updatePhysics() {
            long now = System.currentTimeMillis();

            // Do nothing if mLastTime is in the future.
            // This allows the game-start to delay the start of the physics
            // by 100ms or whatever.
            if (mLastTime > now) return;

            double elapsed = (now - mLastTime) / 1000.0;

            // mRotating -- update heading
            if (mRotating != 0) {
                mHeading += mRotating * (PHYS_SLEW_SEC * elapsed);

                // Bring things back into the range 0..360
                if (mHeading < 0)
                    mHeading += 360;
                else if (mHeading >= 360) mHeading -= 360;
            }

            // Base accelerations -- 0 for x, gravity for y
            double ddx = 0.0;
            double ddy = -PHYS_DOWN_ACCEL_SEC * elapsed;

            if (mEngineFiring) {
                // taking 0 as up, 90 as to the right
                // cos(deg) is ddy component, sin(deg) is ddx component
                double elapsedFiring = elapsed;
                double fuelUsed = elapsedFiring * PHYS_FUEL_SEC;

                // tricky case where we run out of fuel partway through the
                // elapsed
                if (fuelUsed > mFuel) {
                    elapsedFiring = mFuel / fuelUsed * elapsed;
                    fuelUsed = mFuel;

                    // Oddball case where we adjust the "control" from here
                    mEngineFiring = false;
                }

                mFuel -= fuelUsed;

                // have this much acceleration from the engine
                double accel = PHYS_FIRE_ACCEL_SEC * elapsedFiring;

                double radians = 2 * Math.PI * mHeading / 360;
                ddx = Math.sin(radians) * accel;
                ddy += Math.cos(radians) * accel;
            }

            double dxOld = mDX;
            double dyOld = mDY;

            // figure speeds for the end of the period
            mDX += ddx;
            mDY += ddy;

            // figure position based on average speed during the period
            mX += elapsed * (mDX + dxOld) / 2;
            mY += elapsed * (mDY + dyOld) / 2;

            mLastTime = now;

            // Evaluate if we have landed ... stop the game
            double yLowerBound = TARGET_PAD_HEIGHT + mLanderHeight / 2
                    - TARGET_BOTTOM_PADDING;
            if (mY <= yLowerBound) {
                mY = yLowerBound;

                int result = STATE_LOSE;
                CharSequence message = "";
                Resources res = mContext.getResources();
                double speed = Math.sqrt(mDX * mDX + mDY * mDY);
                boolean onGoal = (mGoalX <= mX - mLanderWidth / 2 && mX
                        + mLanderWidth / 2 <= mGoalX + mGoalWidth);

                // "Hyperspace" win -- upside down, going fast,
                // puts you back at the top.
                if (onGoal && Math.abs(mHeading - 180) < mGoalAngle
                        && speed > PHYS_SPEED_HYPERSPACE) {
                    result = STATE_WIN;
                    mWinsInARow++;
                    doStart();

                    return;
                    // Oddball case: this case does a return, all other cases
                    // fall through to setMode() below.
                } else if (!onGoal) {
                    message = res.getText(R.string.message_off_pad);
                } else if (!(mHeading <= mGoalAngle || mHeading >= 360 - mGoalAngle)) {
                    message = res.getText(R.string.message_bad_angle);
                } else if (speed > mGoalSpeed) {
                    message = res.getText(R.string.message_too_fast);
                } else {
                    result = STATE_WIN;
                    mWinsInARow++;
                }

                setState(result, message);
            }
        }
    }

    /** Handle to the application context, used to e.g. fetch Drawables. */
    private Context mContext;

    /** Pointer to the text view to display "Paused.." etc. */
    private TextView mStatusText;

    /** The thread that actually draws the animation */
    private LunarThread thread;

    public LunarView(Context context, AttributeSet attrs) {
        super(context, attrs);

        // register our interest in hearing about changes to our surface
        SurfaceHolder holder = getHolder();
        holder.addCallback(this);

        // create thread only; it's started in surfaceCreated()
        thread = new LunarThread(holder, context, new Handler() {
            @Override
            public void handleMessage(Message m) {
                mStatusText.setVisibility(m.getData().getInt("viz"));
                mStatusText.setText(m.getData().getString("text"));
            }
        });

        setFocusable(true); // make sure we get key events
    }

    /**
     * Fetches the animation thread corresponding to this LunarView.
     * 
     * @return the animation thread
     */
    public LunarThread getThread() {
        return thread;
    }

    /**
     * Standard override to get key-press events.
     */
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent msg) {
        return thread.doKeyDown(keyCode, msg);
    }

    /**
     * Standard override for key-up. We actually care about these, so we can
     * turn off the engine or stop rotating.
     */
    @Override
    public boolean onKeyUp(int keyCode, KeyEvent msg) {
        return thread.doKeyUp(keyCode, msg);
    }

    /**
     * Standard window-focus override. Notice focus lost so we can pause on
     * focus lost. e.g. user switches to take a call.
     */
    @Override
    public void onWindowFocusChanged(boolean hasWindowFocus) {
        if (!hasWindowFocus) thread.pause();
    }

    /**
     * Installs a pointer to the text view used for messages.
     */
    public void setTextView(TextView textView) {
        mStatusText = textView;
    }

    /* Callback invoked when the surface dimensions change. */
    public void surfaceChanged(SurfaceHolder holder, int format, int width,
            int height) {
        thread.setSurfaceSize(width, height);
    }

    /*
     * Callback invoked when the Surface has been created and is ready to be
     * used.
     */
    public void surfaceCreated(SurfaceHolder holder) {
        // start the thread here so that we don't busy-wait in run()
        // waiting for the surface to be created
        thread.setRunning(true);
        thread.start();
    }

    /*
     * Callback invoked when the Surface has been destroyed and must no longer
     * be touched. WARNING: after this method returns, the Surface/Canvas must
     * never be touched again!
     */
    public void surfaceDestroyed(SurfaceHolder holder) {
        // we have to tell thread to shut down & wait for it to finish, or else
        // it might touch the Surface after we return and explode
        boolean retry = true;
        thread.setRunning(false);
        while (retry) {
            try {
                thread.join();
                retry = false;
            } catch (InterruptedException e) {
            }
        }
    }
}