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Draw an area over a Bitmap in C++ Builder?

Posted on 1998-03-02
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i'm trying to write a program that one of its task is let the user to select an area over a bitmap.
The area must be select with a rectangle over this image. The user must press the mouse button,
to select the origin point, and then must move the mouse to the final point, and release the button,
to finish the selection. A rectangle must be painted while the user is moving the mouse from the origin
point to the final point, showing the area selected in each moment.

I've tried to do this with a canvas in a TImage object for the bitmap  but i can't clean every rectangle
that i paint while the mouse is moving to the final point.

      How can i write this program?
      what C++ Builder objects must i use?
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Question by:ineila
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4 Comments
 
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inter earned 300 total points
ID: 1182926
Dear ineila,

Do the following:(I am sure you do it partialy)

1 - Declare int OriginX, OriginY, OldX, OldY; BOOL drawing = false
2 - On MouseDown event of the TImage Set OriginX = x, OriginY = y
3 - On MouseMove event
    if (drawing) {
      Image1->Picture->Bitmap->Canvas->Rectangle(OrigingX,OriginY,OldX,OldY);
      OldX = x; OldY = y;
      Image1->Picture->Bitmap->Canvas->Rectangle(OrigingX,OriginY,OldX,OldY);
    } else {
      Image1->Picture->Bitmap->Canvas->Mode = pmXor; //this is the trick!!!!
      OriginX = x;OriginY = y;
      OldX = x; OldY = y;
      Image1->Picture->Bitmap->Canvas->Rectangle(OrigingX,OriginY,OldX,OldY);
      drawing = TRUE;
    }
4 - On MouseUp event
     if (drawing) {
      Image1->Picture->Bitmap->Canvas->Mode = pmCopy;
      drawing = FALSE;
     }

the idea is that when you want such a restoration, the pmXor mode help. The drawing you have made combines the colors with xor operation. If you draw the same thing second time the image became unaffected.

Need more, as more please
Igor


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LVL 5

Expert Comment

by:inter
ID: 1182927
Excuse me On MouseDown

  if (drawing) {
      Image1->Picture->Bitmap->Canvas->Mode = pmXor; //this is the trick!!!!
      OriginX = x;OriginY = y;
      OldX = x; OldY = y;
      Image1->Picture->Bitmap->Canvas->Rectangle(OrigingX,OriginY,OldX,OldY);
      drawing = TRUE;
  }

and DELETE the OnMouseMove ELSE part

Igor
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LVL 5

Expert Comment

by:inter
ID: 1182928
Awfully sorry,

In previous comment If (drawing) be if (!drawing)..

igor
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Author Comment

by:ineila
ID: 1182929
The answer its good.

I have found another way, this is creating a TShape object over the Timage.
The algorithm is similar, when you press the mouse button i select the
origin position, and when i move the mouse i select the final position. When
mouse button is released the shape takes its final size.


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