CyclicTransitionDrawable.java

package com.darkrockstudios.apps.tminus.misc;

/**
 * NOTICE
 * Based on the TransitionDrawable code from Android Open Source Project
 * http://source.android.com/
 */

import android.graphics.Canvas;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.LayerDrawable;
import android.os.SystemClock;

public class CyclicTransitionDrawable extends LayerDrawable implements Drawable.Callback
{
	protected enum TransitionState
	{
		STARTING,
		PAUSED, RUNNING
	}

	protected Drawable[] drawables;
	protected int        currentDrawableIndex;
	protected int alpha = 0;
	protected int  fromAlpha;
	protected int  toAlpha;
	protected long duration;
	protected long startTimeMillis;
	protected long pauseDuration;

	protected TransitionState transitionStatus;

	public CyclicTransitionDrawable( final Drawable[] drawables )
	{
		super( drawables );
		this.drawables = drawables;
	}

	public void startTransition( final int durationMillis, final int pauseTimeMillis )
	{
		fromAlpha = 0;
		toAlpha = 255;
		duration = durationMillis;
		pauseDuration = pauseTimeMillis;
		startTimeMillis = SystemClock.uptimeMillis();
		transitionStatus = TransitionState.PAUSED;
		currentDrawableIndex = 0;

		invalidateSelf();
	}

	@Override
	public void draw( final Canvas canvas )
	{
		boolean done = true;

		switch( transitionStatus )
		{
			case STARTING:
				done = false;
				transitionStatus = TransitionState.RUNNING;
				break;

			case PAUSED:
				if( (SystemClock.uptimeMillis() - startTimeMillis) < pauseDuration )
				{
					break;
				}
				else
				{
					done = false;
					startTimeMillis = SystemClock.uptimeMillis();
					transitionStatus = TransitionState.RUNNING;
				}

			case RUNNING:
				break;
		}

		// Determine position within the transition cycle
		if( startTimeMillis >= 0 )
		{
			float normalized = (float) (SystemClock.uptimeMillis() - startTimeMillis) / duration;
			done = normalized >= 1.0f;
			normalized = Math.min( normalized, 1.0f );
			alpha = (int) (fromAlpha + (toAlpha - fromAlpha) * normalized);
		}

		if( transitionStatus == TransitionState.RUNNING )
		{
			// Cross fade the current
			int nextDrawableIndex = 0;

			if( currentDrawableIndex + 1 < drawables.length )
			{
				nextDrawableIndex = currentDrawableIndex + 1;
			}

			Drawable currentDrawable = getDrawable( currentDrawableIndex );
			Drawable nextDrawable = getDrawable( nextDrawableIndex );

			// Apply cross fade and draw the current drawable
			currentDrawable.setAlpha( 255 - alpha );
			currentDrawable.draw( canvas );
			currentDrawable.setAlpha( 0xFF );

			if( alpha > 0 )
			{
				nextDrawable.setAlpha( alpha );
				nextDrawable.draw( canvas );
				nextDrawable.setAlpha( 0xFF );
			}

			// If we have finished, move to the next transition
			if( done )
			{
				currentDrawableIndex = nextDrawableIndex;
				startTimeMillis = SystemClock.uptimeMillis();

				transitionStatus = TransitionState.PAUSED;
			}
		}
		else
		{
			getDrawable( currentDrawableIndex ).draw( canvas );
		}

		invalidateSelf();
	}
}