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Guest
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 Posted: Wed Sep 20, 2006 8:31 pm Post subject: redraw a canvas to cleanup artifacts |
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Hi;
I created a form
then I created a canvas
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TCanvas* canvas = Form1->Canvas;
// created a TRect
TRect rect =Rect( 10, 10, 100, 100);
canvas->Brush->Color = clBlack;
canvas->Font->Color = clYellow;
//and finally a TextRect
canvas->TextRect(rect, 20, 20, "some text");
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I then created a button routine that moves the rectangle down on the
canvas. The problem is the area where the rectangle used to be is
still painted black so I end up with a visually larger rectangle al
though it is just a display artifact because re sizing the form clears
it up.
How do I get the canvas to repaint?
Thanks |
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Guest
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| Posted: Wed Sep 20, 2006 8:37 pm Post subject: Re: redraw a canvas to cleanup artifacts |
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On Wed, 20 Sep 2006 15:31:33 GMT, DeKayA (AT) bellsouth (DOT) net wrote:
I stuck an Invalidate() in each button click which does indeed redraw
the entire canvas. But it flashes pretty bad. anyway around this
Assuming Invalidate is the right choice? |
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Clayton Arends
Guest
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| Posted: Wed Sep 20, 2006 8:41 pm Post subject: Re: redraw a canvas to cleanup artifacts |
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<DeKayA (AT) bellsouth (DOT) net> wrote in message
news:45115d37.7620437 (AT) forums (DOT) borland.com...
| Quote: | then I created a canvas
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Perhaps a minor detail but you didn't *create* a canvas. You are
referencing the form's canvas.
| Quote: | How do I get the canvas to repaint?
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Since this canvas belongs to the form, and the form has a window handle, you
can use any API function that acts on a window handle. In this case
Invalidate() and InvalidateRect(). Check them out in the help but here is
an example:
TRect oldRect;
TRect newRect;
InvalidateRect(Form11->Handle, &oldRect, TRUE);
InvalidateRect(Form11->Handle, &newRect, FALSE);
HTH,
- Clayton |
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Guest
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| Posted: Wed Sep 20, 2006 8:45 pm Post subject: Re: redraw a canvas to cleanup artifacts |
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In the news group I saw references to doublebuffer but I didn't see
it as a property for my form I have BCB4
Does it exist. is it the right way to pursue?
On Wed, 20 Sep 2006 15:37:18 GMT, DeKayA (AT) bellsouth (DOT) net wrote:
| Quote: | On Wed, 20 Sep 2006 15:31:33 GMT, DeKayA (AT) bellsouth (DOT) net wrote:
I stuck an Invalidate() in each button click which does indeed redraw
the entire canvas. But it flashes pretty bad. anyway around this
Assuming Invalidate is the right choice?
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Clayton Arends
Guest
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| Posted: Wed Sep 20, 2006 9:22 pm Post subject: Re: redraw a canvas to cleanup artifacts |
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You have to set DoubleBuffered to true in code. In the form's constructor
put this:
DoubleBuffered = true;
- Clayton |
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Guest
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| Posted: Wed Sep 20, 2006 9:32 pm Post subject: Re: redraw a canvas to cleanup artifacts |
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Clayton
Thanks you have been a lot of help.
I tried your first suggestion
static TRect rect;
InvalidateRect(Form1->Handle, &rect, TRUE); // clears the rectangle
rect =Rect( g_RectX, g_RectY, Formwidth-10, g_RectY+Theight);
Application->ProcessMessages(); // Required or rect is not displayed
and it worked great.
not sure why you had two in your example one with it erase false.
didn't seem to make a difference. still required
Application->ProcessMessages();
Not even sure DoubleBuffered will be required now but I will go
experiment with it to see what I can learn
Thanks
On Wed, 20 Sep 2006 09:22:41 -0700, "Clayton Arends"
<nospam_claytonarends (AT) hotmail (DOT) com> wrote:
| Quote: | You have to set DoubleBuffered to true in code. In the form's constructor
put this:
DoubleBuffered = true;
- Clayton
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Hans Galema
Guest
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| Posted: Thu Sep 21, 2006 12:37 am Post subject: Re: redraw a canvas to cleanup artifacts |
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DeKayA (AT) bellsouth (DOT) net wrote:
| Quote: | TCanvas* canvas = Form1->Canvas;
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If that line and the rest of your code is used in an eventhandler
for a TButton on Form1 then there is a much cleaner approch.
Just use the forms property Canvas and delete that line.
Canvas->TextRect(rect, 20, 20, "some text");
Hans. |
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Guest
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| Posted: Thu Sep 21, 2006 1:38 am Post subject: Re: redraw a canvas to cleanup artifacts |
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Is that the difference between canvas and Canvas?
On Wed, 20 Sep 2006 21:37:48 +0200, Hans Galema <notused (AT) notused (DOT) nl>
wrote:
| Quote: | DeKayA (AT) bellsouth (DOT) net wrote:
TCanvas* canvas = Form1->Canvas;
If that line and the rest of your code is used in an eventhandler
for a TButton on Form1 then there is a much cleaner approch.
Just use the forms property Canvas and delete that line.
Canvas->TextRect(rect, 20, 20, "some text");
Hans. |
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Hans Galema
Guest
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| Posted: Thu Sep 21, 2006 3:59 am Post subject: Re: redraw a canvas to cleanup artifacts |
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DeKayA (AT) bellsouth (DOT) net wrote:
| Quote: | Is that the difference between canvas and Canvas?
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Sorry. What do you mean with that question?
Hans. |
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