protected override void OnDraw(Android.Graphics.Canvas canvas)
{
// if our render buffers are not valid, generate them
if (CurrWidth != this.LayoutParameters.Width || CurrHeight != this.LayoutParameters.Height)
{
CreateTextBitmaps(this.LayoutParameters.Width, this.LayoutParameters.Height);
CreateResultBitmaps(this.LayoutParameters.Width, this.LayoutParameters.Height);
CurrWidth = this.LayoutParameters.Width;
CurrHeight = this.LayoutParameters.Height;
}
// keep the spot light centered on the image
float xPos = (LayoutParameters.Width / 2) - ((AlphaMask.Width / 2) * MaskScale);
float yPos = (LayoutParameters.Height / 2) - ((AlphaMask.Height / 2) * MaskScale);
// update the text's transform for the mask scale.
// The text's transform should be the inverse of the Canvas' values
TextTransform.SetScale(1.0f / MaskScale, 1.0f / MaskScale);
TextTransform.PreTranslate(-xPos, -yPos);
TextPaint.Shader.SetLocalMatrix(TextTransform);
// clear the bitmap before re-rendering. (NOT EFFICIENT _AT_ _ALL_)
ResultBmp.SetPixels(new int[ResultBmp.RowBytes * ResultBmp.Height], 0, ResultBmp.RowBytes, 0, 0, ResultBmp.Width, ResultBmp.Height);
// save / restore the canvas settings so we don't accumulate the scale
ResultCanvas.Save();
ResultCanvas.Translate(xPos, yPos);
ResultCanvas.Scale(MaskScale, MaskScale);
// render the alpha mask'd text to our result bmp
ResultCanvas.DrawBitmap(AlphaMask, 0, 0, TextPaint);
// restore the canvas values for next time.
ResultCanvas.Restore();
// and to the actual android buffer, render our result
canvas.DrawBitmap(ResultBmp, 0, 0, null);
}