How crop bitmap in selected area using firemonkey?

Question

I need create a crop effect to my app. I have a TRectangle over a TImage, and I need when the user press the save button, copy just the area that the TRectangle uses. There is some way that I can cut just a specific area from the Image1.Bitmap? I printed a image to better ilustrate what I need:

You better use a canvas which you can control the scale. Don't just use any random image control. If it were me, I'd write a custom control for this. But it wouldn't be a very trivial one. — Jerry Dodge
What is the WrapMode that you use? What if it's Tile and your selector covers more than one tile of the displayed image? — Victoria
The crop procedure would be like this: 1) calculate the scaling of your image and convert the rectangles bounds to the image scale. 2) create a TBitmap and use CopyFromBitmap with the calculated rectangle. This copies a section from your TImage bitmap to the new bitmap. 3) assign the bitmap to your TImage bitmap (if that's what you want). — Hans
Can you please give me a code example on how to do the step number 2? — Diego Bittencourt
The concept is very trivial: Draw your image on a controlled canvas (one which you have 100% control over), and do simple math to determine scale. Surely there are plenty of resources how to extract a portion of an image in Firemonkey. I used them to write my own vector signature control. Only much simpler for you. But please don't expect us to write it for you. — Jerry Dodge

asd-tm asd-tm · Accepted Answer · 2017-11-01T14:14:32

Here is a sample that works for me:

procedure TForm1.Button1Click(Sender: TObject);
var
  Bmp: TBitmap;
  xScale, yScale: extended;
  iRect: TRect;
begin

  Bmp := TBitmap.Create;
  xScale := Image1.Bitmap.Width / Image1.Width;
  yScale := Image1.Bitmap.Height / Image1.Height;
  try
    Bmp.Width := round(Rectangle1.Width * xScale);
    Bmp.Height := round(Rectangle1.Height * yScale);
    iRect.Left := round(Rectangle1.Position.X * xScale);
    iRect.Top := round(Rectangle1.Position.Y * yScale);
    iRect.Width := round(Rectangle1.Width * xScale);
    iRect.Height := round(Rectangle1.Height * yScale);
    Bmp.CopyFromBitmap(Image1.Bitmap, iRect, 0, 0);
    Image2.Bitmap := Bmp
  finally
    Bmp.Free;
  end;
end;

I assume here that Rectangle1 has Image1 as its Parent:

Otherwise you will need to consider the offset of Position.X and Position.Y properties.

Here is a result of procedure functioning:

How crop bitmap in selected area using firemonkey?

1 Answers