Android Question draw bitmap with alpha

[ilan]

hi

can i draw a bitmap via canvas with alpha 100 for example?

thanx

 

[sorex]

sure, it will copy alpha levels if it has any (png)

 

[ilan]

sure, it will copy alpha levels if it has any (png)

i mean i have a bitmap already and i want to change his alpha via code and use it in a panel or imageview

i could directly change the opacity of the view instead but i would like to know if it is possible to change the alpha of a bitmap like here

http://stackoverflow.com/questions/5118894/how-to-change-a-bitmaps-opacity

 

[sorex]

you could read a pixel alter the alpha and store it again but that would be way too slow.

there might be faster techniques to do that tho.

 

[JordiCP]

In the same link you provided, the third answer gives the way to go. It will not change the bitmap alpha since it can be inmutable, but will generate a alpha copy

A tested approach using the idea given there is (uses inline Java but could also be done with just Javaobjects)

Sub CreateBitmapWithAlpha(myOriginalBitmap As Bitmap, newAlpha As Int) As Bitmap
  Dim canvas1 As Canvas
  Dim myNewBitmap As Bitmap
  myNewBitmap.initializeMutable(myOriginalBitmap.Width,myOriginalBitmap.Height)
  canvas1.initialize2(myNewBitmap)
 
  Dim CanvJO As JavaObject = canvas1
  CanvJO = CanvJO.GetField("canvas")  
 
  Dim J As JavaObject
  J.initializeContext()
  J.Runmethod("alphatize",Array(CanvJO,myOriginalBitmap,newAlpha))
  Return(myNewBitmap)

End Sub

Your Java code

import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Rect;

public void alphatize(Canvas mCanvas, Bitmap mBitmap, int mAlpha){
  Paint paint =new Paint();
  paint.setAlpha(mAlpha);
  Rect mDstRect = new Rect(0,0,mBitmap.getWidth(),mBitmap.getHeight()); //We are assuming they are the same size
  mCanvas.drawBitmap(mBitmap, null, mDstRect, paint);
}