bitmap

[rowgram]

I've got a bitmap of an XY plot that I would like to fix in place on a form (at some point later, there will be a cursor that moves around the plot depending upon the xy values input).

Here's the loading of the bitmap :
Graphics* gr = CreateGraphics();
Bitmap* plot = new Bitmap(S"plot.bmp");
gr->DrawImage(plot, 50, 20);
this->Update();

I can incorporate this 2 ways :

via a button click event handler :

in this case, everything works fine except any window opened in fron tof the form causes the bitmap to erase - it's as if the this->Update() function is performing a re-paint ?


via the Form_Paint event handler (this would be my preferred way) :

in this case, the form loads fine, then I open a file via OpenFileDialog & Iget an unhandled exception : invalid parameter for the statement :
if(ofd->ShowDialog==DialogResult::OK)
This occurs even if I change OK to Cancel or anyother Dialog Result value.
It seems like the constant re-painting of the bitmap doesn't allow for any other dialog to operate - is this true ?

Regards,
ak

[Marc G]

Using the paint handler is defintely the right way to do this. Basically: all drawing in windows should be done in your paint handler to avoid the 'tearing' problem when moving a window in front of your window.

[rowgram]

This is my intent, but why does the introduction of an openfile dialog cause the error ? Am I loading & updating the bitmap correctly ?
Does this->Update() not allow for any other process ?

[Marc G]

You should not call Update in your paint handler, it will recursively keep calling your paint handler.

[rowgram]

Here is what I have inside the paint handler :

Graphics* gr = CreatGraphics();
Bitmap* plot = new Bitmap(S"plot.bmp");
gr->DrawImage(plot, 50, 20);
Update();

Is this the way to use Update() ?

[Marc G]

No. You should not call Update in your paint handler. Remove it.
When you do call Update in your paint handler, your paint handler will be called recursively.

[rowgram]

I'm confused - could you please clarify your statement ?

In your earlier message you say to call Update in the paint handler, your latest statement says not to call Update in the paint handler.

[Marc G]

Sorry, that was my fault. I made a typo in my first reply and have now fixed it. :blush:

So to set it straight: do not call Update in your paint handler.

[rowgram]

No problem. OK, so now I have :

Graphics*gr = CreateGraphics();
Bitmap* plot = new Bitmap(S"plot.bmp");
gr->DrawImage(plot, 50, 20);

inside Form_Paint. But there still seems to be a conflict with OpenFileDialog.
The program compiles, runs & I see the bitmap displayed - you're right, now there is no 'tearing', but the problem starts when I open a file that I need : it results in an unhandled exception : Invalid Parameter used . This shows up on the statement :

if (ofd->ShowDialog()==DialogResult::OK)

(ofd is my instance of OpenFileDialog. I get the feeling there is some competing of resources...but I don't know, I'm new to C++ . Any suggestions ?

[rowgram]

Here's what I got to work :

inside the Form_Paint handler :

Graphics * gr = e->Graphics;
if (bitmap !+ NULL)
{ gr->DrawImage(bitmap, x-left, x-right, width, height);}

inside a button click handler :

bitmap = new Bitmap(S"file name.bmp");
this->Invalidate();
this->Update();

inside the Form definition :
private: static Bitmap* bitmap;

[Marc G]

if (bitmap !+ NULL)
I guess you mean:
if (bitmap != NULL)