CODEWITHSUNDEEP
androidbitmapandroid-canvascrop
user123456
user123456

Reputation: 123

How to draw Bitmap from ARGB_8888 Bitmap

I am drawing paths on canvas and creating Transparent bitmap while saving and creating cropping bitmap from transparent bitmap.

See Images : enter image description here

In this I mage I am drawing path on canvas and I am creating transparent bitmap and according to startX,lowestY and highestX,highestY 

Bitmap cropBitmap =Bitmap.createBitmap(sourceBitmap,startX,lowestY,highestX,highestY);

When I am cropping Bitmap I want Only "Test" drawing crop bitmap.But it's giving empty bitmap. Like this

enter image description here

Inside red box I want cropped bitmap from transparent bitmap whatever I draw on canvas.

Upvotes: 0

Views: 622

Answers (1)

abc
abc

Reputation: 2037

You cannot simply create a transparent bitmap, and assume that whatever is within the bounds of the bitmap has become a part of it meaning that the pixels are identical. There are two problems with your assumption, number 1, a transparent bitmap won't help because transparency serves as a see through bitmap which only will have alpha value, number 2, the data that is drawn with the path, has no correlation to the data of your bitmap, you initially created a bitmap with no color, except that it's completely transparent.

Here's the general code for the correct way how to achieve such a task:

 class myDrawingView extends View() {
      // all your class members you initialize here
      @Override
      public void onDraw(Canvas canvas) {
          // get your width and height using startx, starty, highestx, highesty, lowesty
          Bitmap buffer = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
          canvas.setBitmap(buffer);
          canvas.drawPath(//draw your path here);
          invalidate();

      }

The Bitmap called buffer, now is the frame buffer for all your drawing so you can draw a path and that will be rendered on the buffer you defined. And you see that no transparency was used we just simply created a bitmap with no pixels assigned to it at first, once you draw to it via the canvas, your bitmaps pixels will be whatever you drew.

Upvotes: 1

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