help with re-paint

[rowgram]

I need to create a filled rectangle with coordinates that loop :

for (j=0; j<max; j++)
{
Graphics* gr2 = CreateGraphics();
gr2->FilledRectangle(...j...);
}

How can I make it re-paint ?
I tried putting same code above into Form_Paint event handler, without the for loop, but the filled rectangles still 'tear' when a window is placed in front of it.
How can I repaint this object that changes its shape with variable j ?

Also I'm confused on the difference between
Graphics * gr2 = e->Graphics; & Graphics* gr = CreateGraphics();

Can someone clarify this ?

ak

[rowgram]

I think the right thing to do is to use the PaintEventArgs :
Graphics * gr = e->Graphics;
// I draw a bitmap using gr->DrawImage

but gr->FillRectangle (...j...) doesn't seem to repaint, even though the bitmap does. Why ?

[Marc G]

What exactly do you mean with "doesn't repaint"?
What do you want to achieve?
Can you post your entire paint handler?

[rowgram]

Here is what I have :
private: System::Void Form2_Paint(System::Object * sender, System::Windows::Forms::PaintEventArgs * e)
{

Graphics * gr = e->Graphics;
if (bitmap != NULL)
{
gr->DrawImage(bitmap, 20, 10, 500, 500);
}


SolidBrush* sb = new SolidBrush(Color::Red);
gr->FillRectangle(sb, 300 + data[j] *10, 300 - data[j] *10, 2, 2);

}

private: System::Void button2_Click(System::Object * sender, System::EventArgs * e)
{
...

for (j=0;j<dwell_samples; j++)
{
Graphics* gr = CreateGraphics();
SolidBrush* sb = new SolidBrush(Color::Red);
gr->FillRectangle(sb, 300 + data[j] *10, 300 - data[j] *10, 2, 2);
}
...
}


The Bitmap refreshs (after minimizing, maximizing, moving other windows in front of the form), but the red rectangles do not refresh ?

[Marc G]

All drawing code should happen in your paint handler. That's the way Windows work. When a part of you window need to be redrawn because you restored it or moved another window in front of it, Windows will send a WM_PAINT message to your window. In your case this WM_PAINT is handled byb your paint handler. That's why all the drawing code needs to be in that function.

[rowgram]

OK - I've tried this & now no red rectangles appear (i.e. I have no image to refresh !) ... this is because the rectangles involve the var j, which every time is incremented, should cause a red rectangle to be painted. By putting all the code into the Paint Handler, the only time the red rectangles will be created is for WM_Paint messages !
How can I trigger the rectangles to paint inside

Also, I think CreateGraphics() method is meant for creating graphics objects outside of the Paint Event Handler - is this not correct ?

[Marc G]

If you want to trigger your WM_PAINT handler you need to invalidate your window. You can use the Invalidate (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfsystemwindowsformscontrolclassinvalidatetopic.asp) method for that.