Here&#39;s an excellent article with illustrations by a Google engineer:

http://ssp.impulsetrain.com/porterduff.html

PorterDuff is described as a way of combining images as if they were &quot;irregular shaped pieces of cardboard&quot; overlayed on each other, as well as a scheme for blending the overlapping parts.

The default Android way of composing images is &lt;a href=&quot;http://developer.android.com/reference/android/graphics/PorterDuff.Mode.html#SRC_OVER&quot;&gt;PorterDuff.Mode.SRC_OVER&lt;/a&gt;, which equates to drawing the source image/color &lt;i&gt;over&lt;/i&gt; the target image. In other words, it does what you would expect and draws the source image (the one you&#39;re drawing) on top of the destination image (the canvas) with the destination image showing through to the degree defined by the source image&#39;s alpha.


![PorterDuff infographic from the article][1]

You can use the key below to understand the algebra that &lt;a href=&quot;http://developer.android.com/reference/android/graphics/PorterDuff.Mode.html&quot;&gt;the Android docs&lt;/a&gt; use to describe the other modes (see &lt;a href=&quot;http://ssp.impulsetrain.com/porterduff.html&quot;&gt;the article&lt;/a&gt; for a fuller desription with similar terms).

&lt;ul&gt;
  &lt;li&gt;&lt;b&gt;Sa&lt;/b&gt; Source alpha&lt;/li&gt;
  &lt;li&gt;&lt;b&gt;Sc&lt;/b&gt; Source color&lt;/li&gt;
  &lt;li&gt;&lt;b&gt;Da&lt;/b&gt; Destination alpha&lt;/li&gt;
  &lt;li&gt;&lt;b&gt;Dc&lt;/b&gt; Destination color&lt;/li&gt;
&lt;/ul&gt;

Where alpha is a value &lt;code&gt;[0..1]&lt;/code&gt;, and color is substituted once per channel (so use the formula once for each of red, green and blue)

The resulting values are specified as a pair in square braces as follows.

    [&lt;alpha-value&gt;,&lt;color-value&gt;]

Where &lt;code&gt;alpha-value&lt;/code&gt; and &lt;code&gt;color-value&lt;/code&gt; are formulas for generating the resulting alpha chanel and each color chanel respectively.


  [1]: http://i.stack.imgur.com/B9syg.png

It defines how to compose images based on the alpha value. See more here http://en.wikipedia.org/wiki/Alpha_compositing

**Note:** this is mostly for debugging and understanding KnockoutJS.

Is there a way to explicitly request Knockout to refresh the view from (already bound) view model? I am looking for something like: 

    ko.refreshView();

I understand that this is not an intended use of Knockout, but I still want to know if there is a such method for debugging and learning purposes.

How to force a view refresh without having it trigger automatically from an observable?

&gt; **Possible Duplicate:**  
&gt; [What&amp;#39;s the difference between is_null($var) and ($var === null)?](https://stackoverflow.com/questions/4662588/whats-the-difference-between-is-nullvar-and-var-null)  

&lt;!-- End of automatically inserted text --&gt;

PHP has two (that I know of, and three if you count `isset()`) methods to determine if a value is null: `is_null()` and `=== null`.  I have heard, but not confirmed, that `=== null` is faster, but in a code review someone strongly suggested that I use `is_null()` instead as it is specifically designed for the null-evaluation purpose.  He also started talking about math or something.

Anyway, the fact that `is_null()` is apparently slower also leads me to believe that it&#39;s doing more than `=== null` does and is probably preferred.  Is there any reason to use one or the other?  Is one always preferred?  What about `isset()`?

As an addendum to possibly not get this question closed, what about `isset()` vs. `is_null()`?  It seems that all `isset()` will do is suppress the notice, so unless you actually *want* a notice for an undefined variable, any reason to use `is_null()` instead?  How about if you know the variable is initialized at the time?

Finally, is there any mathematical reason to prefer `is_null()` over `=== null`?  Something about null not being comparable?

is_null($x) vs $x === null in PHP

I would like to know what **PorterDuff.Mode** means in android graphics.

I know that it is a *transfer mode*. 

I also know, that it has attributes such as DST_IN, Multiply etc.

What does PorterDuff.Mode mean in android graphics.What does it do?

I would like to know what PorterDuff.Mode means in android graphics.
I know that it is a transfer mode.
I also know, that it has attributes such as DST_IN, Multiply etc.

I would like to finish an activity from inside the `onCreate` method. When I call `finish()`, `onDestroy()` is not immediately called, the code keeps flowing past `finish()`. `onDestroy()` isn&#39;t called until after the `onCreate()` closing brace.

Per the `onCreate()` description at developer.android.com/reference.

&gt; You can call finish() from within this function, in which case
&gt; onDestroy() will be immediately called without any of the rest of the
&gt; activity lifecycle (onStart(), onResume(), onPause(), etc) executing.

Reason I ask is: I would like to check data from the Bundle passed to `onCreate()`. Of course I have control of what is passed to `onCreate`, but I still think it should be checked at the point of delivery.

My code contains class `A`, which starts Activity `B`. I believe the last two &quot;outside of if clause&quot; tags, shouldn&#39;t be called because the `finish` method in the `if` statement should have destroyed the activity.  It has nothing to do with the if clause because the tag line after the second `finish()` call is still also read.

My Code:

Class A

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
            
        // goToBButton: when pressed sends message to class B.    
        Button goToBButton = (Button)this.findViewById(R.id.go_to__b_btn);
        goToBButton.setOnClickListener(new OnClickListener() {
        	@Override
            public void onClick (View v) {    	
        		Log.i(TAG,&quot;A Class: goToBButton, onClick&quot;);
        		Intent i = new Intent(A.this, B.class);
      			startActivityForResult(i,REQ_TO_B);
        	}     	
        });                
    } // end onCreate

My Code ClassB

        public class B extends Activity{

	private static final String TAG = &quot;tag&quot;;
	
	@Override
       public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.layoutb);
      
      // set as true, should always print Tag: one line before first finish&quot;
      if (true)  {
      	
      	Log.i(TAG,&quot;B Class: one line before 1st finish&quot;);
        finish();
      }
       
      // shouldn&#39;t get here after first finish
      Log.i(TAG,&quot;B Class: outside of if clause, before second finish&quot;);
      finish();
      // shouldn&#39;t get here after second finish
      Log.i(TAG,&quot;B Class: outside of if clause, after finish&quot;);                  
       } // end onCreate
	

	@Override
	public void onStart () {
		super.onStart();
		Log.i(TAG,&quot;B Class: onStart&quot;);
	}
	
	@Override
	public void onRestart() {
		super.onRestart();
		Log.i(TAG,&quot;B Class: onRestart&quot;);
	}
	
	@Override
	public void onResume () {
		super.onResume();
		Log.i(TAG,&quot;B Class: onResume&quot;);
	}
	
	@Override
	public void onPause () {
		super.onPause();
		Log.i(TAG,&quot;B Class: onPause&quot;);
	}
	
	@Override
	public void onStop () {
		super.onStop();
		Log.i(TAG,&quot;B Class: onStop&quot;);
	}
	
	@Override
	public void onDestroy () {
		super.onDestroy();
		Log.i(TAG,&quot;B Class: onDestroy&quot;);
	}
	
     } // end B Class

Here are the results of my tags:

&gt; 11-26 15:53:40.456: INFO/tag(699): A Class: goToBButton, onClick
&gt; 
&gt; 11-26 15:53:40.636: INFO/tag(699): A Class: onPause
&gt; 
&gt; 11-26 15:53:40.865: INFO/tag(699): B Class: one line before 1st finish
&gt; 
&gt; 11-26 15:53:40.896: INFO/tag(699): B Class: outside of if clause,
&gt; before second finish
&gt; 
&gt; 11-26 15:53:40.917: INFO/tag(699): B Class: outside of if clause,
&gt; after finish
&gt; 
&gt; 11-26 15:53:41.035: INFO/tag(699): A Class: onResume
&gt; 
&gt; 11-26 15:53:41.165: INFO/tag(699): B Class: onDestroy

onCreate flow continues after finish()

http://marakana.com/tutorials/android/2d-graphics-example.html

I am using this example below. But when I move my fingers too fast across the screen the line turns to individual dots.

I am not sure whether I can speed up the drawing. Or I should connect the two last points with a straight line. The second of these two solutions seems like a good option, except when moving your finger very fast you will have long sections of a straight line then sharp curves.

If there are any other solutions it would be great to hear them.

Thanks for any help in advance.

Android How to draw a smooth line following your finger

I have one problem with Android `SQLite` database.

I have one table which contains one field.StudentFname
and that application is working fine with Android 2.3.1 and now if I add another field then my application is not working properly. 

Can anyone help me who knows database very well,


How to add new Column to Android SQLite Database?

I want to calculate `dp` from `px` programmatically. How to do it?
I get resolution from:
      
    DisplayMetrics displaymetrics = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(displaymetrics);
    ht = displaymetrics.heightPixels;
    wt = displaymetrics.widthPixels;

        

How to calculate dp from pixels in android programmatically

Given an APK, is it possible to determine which version of Android platform it targets?

Android: How to find which platform version an APK targets?

I don&#39;t have the option to use but OpenGL methods (that is `glxxx()` methods). I need to draw text using gl methods only. After reading the red book, I understand that it is possible only through the `glBitmap()` method. If this is the only possible way, then can any one help me with the pixel array information for all the characters. Is there is any other way to draw text?

How to draw text using only OpenGL methods?

I have used WPF&#39;s 3D capabilities for learning, and for a few implementations, and I have found it to be very capable, and I am also learning DirectX 11, and it is very tricky compared to using 3D classes in WPF. I have only used WPF 3D for very basic stuff, my question is:

Is WPF 3D equally good for advanced applications such as 3D modelling tools, game engines and 3D simulations etc to be an alternative to DirectX and OpenGL?

If there is anything else in the same league, please mention it too.

Is WPF 3D good alternate of DirectX and OpenGL for complex applications?

Currently I am using this command to extract the images:

    ffmpeg -i input.mp4 output_%03d.jpeg

But how can I improve the JPEG image quality?

How can I extract a good quality JPEG image from a video file with ffmpeg?

I want to scale a `System.Drawing.Bitmap` to at least less than some fixed width and height. This is to generate thumbnails for an image gallery on a website, so I want to keep the aspect ratio the same.

I have some across quite a few solutions but none seem to really do what I need; they revolve around scaling based on keeping the width or the height the same but not changing both.

An example:

If I have a 4272 by 2848 image and I want to scale it to a size of 1024 by 768, then the resulting image should be 1024 by 683 and padded (with a black border) to 1024 by 768.

How can I do this with images larger than the required size and smaller than the require sized and also pad images which don&#39;t come out to the exact size I need once scaled?

Scaling a System.Drawing.Bitmap to a given size while maintaining aspect ratio

Can I draw with anti-aliasing on canvas?

I need my circles and line have smooth edges.

Can I draw with antialiasing on canvas?

Having a rich UI application in which I want to show image with complex shape like this

![enter image description here][1]

Now what I want is to crop my image as per Mask image, Actually *image is coming dynamic and can be imported from Camera or Gallery(square or rectangle shape)* and I want that image to fit in my layout frame like above

So just wondering that how do I have achieve this? Any idea /hint welcome

**Background frame**   
![enter image description here][2]  
**Mask**  
![enter image description here][3]

Like [**this**][4] 


  [1]: http://i.stack.imgur.com/ypL2C.jpg
  [2]: http://i.stack.imgur.com/jISCR.png
  [3]: http://i.stack.imgur.com/cJI3J.png
  [4]: https://stackoverflow.com/questions/5299452/how-can-i-crop-an-image-with-mask-and-combine-it-with-another-image-background

Content Type	Original Author	Original Content on Stackoverflow
Question	rogerstone	View Question on Stackoverflow
Solution 1 - Android	Phasmal	View Answer on Stackoverflow
Solution 2 - Android	yoah	View Answer on Stackoverflow

What does PorterDuff.Mode mean in android graphics.What does it do?

Android Problem Overview

Android Solutions

Solution 1 - Android

Solution 2 - Android

is_null($x) vs $x === null in PHP

How to force a view refresh without having it trigger automatically from an observable?

Attributions