Change size of canvas by click

Question

There is a circle made with the help of canvas method MainForm -> Canvas -> Ellipse(350,100,550,300). The question is to change size of canvas by clicking "+" or "-" buttons. Are there any methods?

Answer 1

for resizing ellipse:

1. create some global or Form member variables:

   • int x0=350,y0=100,x1=550,y1=300;
   • this holds the ellipse parameters

2. create some draw function (member to form or not)

   • for example:

     void draw(TCanvas *scr)
      {
      scr->Pen->Color=clWhite;
      scr->Brush->Color=clBlack;
      scr->FillRect(TRect(0,0,MainForm->ClientWidth,MainForm->ClientHeight));
      scr->Brush->Color=clBlue;
      scr->Ellipse(x0,y0,x1,y1);
      }
     

   • create events on resize and on paint for the main form and add draw(Canvas); call in booth

   • that will repaint your form when needed

3. create on (mouse) click event

   • inside you have calling variables X,Y,Shift holding mouse state
   • so simply add this to it
   • x1=X; y1=Y; draw(Canvas);

That is all ... hope I did not make some typo (wrote from memory directly here)

If you need to resize the form then:

• instead of x1=X, y1=Y; do
• ClientWidth=X+32; ClientHeight=Y+32;
• or use SetBounds(Left,Top,X+32,Y+32);
• the +32 is resize area to ensure you can also enlarging ...

[edit1] did miss the +/- buttons (I assumed mouse resize) so here are the buttons

1. create on + button click event:

   • leave the existing code as is and add to the event code this

     int cx=(x0+x1)>>1,ax=(x1-cx); ax+=16; x0=cx-ax; x1=cx+ax;
     int cy=(y0+y1)>>1,ay=(y1+cy); ay+=16; y0=cy-ay; y1=cy+ay; draw(Canvas);
     

   • that will enlarge booth semi-axises by 16 on each click

2. create on - button click event:

   • code is similar to +

     int cx=(x0+x1)>>1,ax=(x1-cx); ax-=16; if (ax<1) ax=1; x0=cx-ax; x1=cx+ax;
     int cy=(y0+y1)>>1,ay=(y1+cy); ay-=16; if (ay<1) ay=1; y0=cy-ay; y1=cy+ay; draw(Canvas);
     

   • that will shrink booth semi-axises by 16 on each click and stop on size 1

if you need the form to resize then adapt the above code ... like in the on mouse event example