BouncyBall: Prefer to run the test at 60Hz

package com.prefabulated.bouncyball;

import android.hardware.display.DisplayManager;

import android.os.Bundle;

import android.os.Trace;

import android.util.Log;

import android.view.Display;

import android.view.Window;

import android.view.WindowManager;

import androidx.appcompat.app.AppCompatActivity;

import java.util.concurrent.Executors;

public class BouncyBallActivity extends AppCompatActivity {

    private static final String LOG_TAG = "BouncyBall";

    private static final float DESIRED_FRAME_RATE = 60.0f;

    private int mDisplayId = -1;

    private float mFrameRate;

    private final DisplayManager.DisplayListener mDisplayListener =

            new DisplayManager.DisplayListener() {

                @Override

                public void onDisplayAdded(int ignored) { /* Don't care. */ }

                @Override

                public void onDisplayRemoved(int ignored) { /* Don't care. */ }

                @Override

                public void onDisplayChanged(int displayId) {

                    if (displayId != mDisplayId) {

                        return;

                    }

                    mFrameRate = getDisplay().getMode().getRefreshRate();

                    Log.d(LOG_TAG, "Using frame rate " + mFrameRate + "Hz");

                }

            };

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        Trace.beginSection("BouncyBallActivity onCreate");

        setContentView(R.layout.activity_bouncy_ball);

        DisplayManager manager = getSystemService(DisplayManager.class);

        manager.registerDisplayListener(Executors.newSingleThreadExecutor(),

                                        DisplayManager.EVENT_TYPE_DISPLAY_REFRESH_RATE,

                                        mDisplayListener);

        setFrameRatePreference();

        Trace.endSection();

    }

    // If available at our current resolution, use 60Hz.  If not, use the

    // lowest refresh rate above 60Hz which is available.  Otherwise, throw

    // an exception which kills the app.

    //

    // The philosophy is that, for now, we only require this test to run

    // solidly at 60Hz.  If a device has a higher refresh rate than that,

    // we slow it down to 60Hz to make this easier to pass.  If a device

    // isn't able to go all the way down to 60Hz, we use the lowest refresh

    // rate above 60Hz.  If the device only supports below 30Hz, that's below

    // our standards so we abort.

    private void setFrameRatePreference() {

        float preferredRate = Float.POSITIVE_INFINITY;

        Display display = getDisplay();

        Display.Mode currentMode = display.getMode();

        mDisplayId = display.getDisplayId();

        mFrameRate = currentMode.getRefreshRate();

        if (mFrameRate == DESIRED_FRAME_RATE) {

            Log.d(LOG_TAG, "Already running at " + mFrameRate + "Hz");

            // We're already using what we want.  Nothing to do here.

            return;

        }

        for (Display.Mode mode : display.getSupportedModes()) {

            if ((currentMode.getPhysicalHeight() != mode.getPhysicalHeight())

                    || (currentMode.getPhysicalWidth() != mode.getPhysicalWidth())) {

                // This is a different resolution; we'll skip it.

                continue;

            }

            float rate = mode.getRefreshRate();

            if (rate == DESIRED_FRAME_RATE) {

                // This is exactly what we were hoping for, so we can stop

                // looking.

                preferredRate = rate;

                break;

            }

            if ((rate > DESIRED_FRAME_RATE) && (rate < preferredRate)) {

                // This is the best rate we've seen so far in terms of being

                // closest to our desired rate without being under it.

                preferredRate = rate;

            }

        }

        if (preferredRate == Float.POSITIVE_INFINITY) {

            String msg = "No display mode with at least " + DESIRED_FRAME_RATE + "Hz";

            throw new RuntimeException(msg);

        }

        Log.d(LOG_TAG, "Changing preferred rate from " + mFrameRate + "Hz to "

                + preferredRate + "Hz");

        Window window = getWindow();

        WindowManager.LayoutParams params = window.getAttributes();

        params.preferredRefreshRate = preferredRate;

        window.setAttributes(params);

    }

}