title: BitmapTransformation in the Glide library not working as expected
body: <p>I'm new to the Glide library, following the Transformations guide found here: <a href="https://github.com/bumptech/glide/wiki/Transformations" rel="noreferrer">https://github.com/bumptech/glide/wiki/Transformations</a></p>
  
  <p>I'm trying to create a custom transformation, but when I place a breakline in the Transformation class's <code>transform</code> method, I can see that it is never called.</p>
  
  <p>Below is my code:</p>
  
  <pre><code>private static class CustomTransformation extends BitmapTransformation {
  
      private Context aContext;
  
      public CustomTransformation(Context context) {
          super(context);
          aContext = context;
      }
  
      @Override
      protected Bitmap transform(BitmapPool pool, Bitmap toTransform, int outWidth, int outHeight) {
          return bitmapChanger(toTransform, 1080, (int) aContext.getResources().getDimension(R.dimen.big_image));
      }
  
      @Override
      public String getId() {
          return "some_id";
      }
  
  }
  
  private static Bitmap bitmapChanger(Bitmap bitmap, int desiredWidth, int desiredHeight) {
      float originalWidth = bitmap.getWidth();
      float originalHeight = bitmap.getHeight();
  
      float scaleX = desiredWidth / originalWidth;
      float scaleY = desiredHeight / originalHeight;
  
      //Use the larger of the two scales to maintain aspect ratio
      float scale = Math.max(scaleX, scaleY);
  
      Matrix matrix = new Matrix();
  
      matrix.postScale(scale, scale);
  
      //If the scaleY is greater, we need to center the image
      if(scaleX &lt; scaleY) {
          float tx = (scale * originalWidth - desiredWidth) / 2f;
          matrix.postTranslate(-tx, 0f);
      }
  
      return Bitmap.createBitmap(bitmap, 0, 0, (int) originalWidth, (int) originalHeight, matrix, true);
  }
  </code></pre>
  
  <p>I've tried initiating Glide in two ways:</p>
  
  <pre><code>Glide.with(this).load(url).asBitmap().transform(new CustomTransformation(this)).into(imageView);
  </code></pre>
  
  <p>and</p>
  
  <pre><code>Glide.with(this).load(url).bitmapTransform(new CustomTransformation(this)).into(imageView);
  </code></pre>
  
  <p>But neither work. Any ideas? Again, I'm not looking for advice on the Matrix itself, I just don't understand why <code>transform(...)</code> isn't being called at all. Thanks!</p>