C# GDI+ line rendering problem...

[news]

This may be a stupid question, but if I don't ask I'll never know

Ok, here it goes.... I am writing an application that renders an image in
one picturebox and a graph in another.

The image is drawn by loading a jpg into a bitmap and then setting
picturebox.image = mybitmap. Ive created my own class, inheriting from the
picturebox and overriding the OnPaint event so I can do e.Graphics.DrawImage
(this.image....). This renders correctly, without flicker and without
problems.

The problem comes with the graph... Im drawing the graph using GDI+ methods
with :-

myGraphic = PictureBox.CreateGraphics ();
myGraphic.DrawLine (....);
etc.

I do this each time I believe the graph has changed.

The problem comes when I move a popup window across the two pictureboxes...
The image renders correctly but the graph will not and the popup window
erases the graph below it.

Ideally, I'd like to render the graph in a similar way to the image but I
can't find how to draw a line in a bitmap - I could write a line drawing
function but that seems a little extreme

Can anyone help ? I think I need to render the graph into a bitmap and then,
in the OnPaint event, blit it to the screen... but how ?

Thanks for any help and sorry if this is obvious or stupid,

Todd

 

[Guest]

To braw a line on am image you need to use the graphics object, so for
example in the code below you create a new bitmap (you can use a pre-existing
image) and draw a line on it:

//Create a new bitmap to draw onto
Bitmap b = new
Bitmap(100,100,System.Drawing.Imaging.PixelFormat.Format24bppRgb);

Graphics g;
Pen p;
Point p1, p2;

try
{
//create graphics object that will allow us to draw on our bitmap
//notice how the bitmap is passed to the function
g = Graphics.FromImage(b);

//set up drawing object
p = new Pen(Color.Red);
p1 = new Point(0,0);
p2 = new Point(50,50);

//draw the line onto the bitmap
g.DrawLine(p, p1, p2);
}
finally
{
//important to make sure we tidy up
g.Dispose();
p.Dispose();
}


Now in your OnPaint method you just write the bitmap image to the control.

Hope that starts you in the right direction.

Mark.

 

[news]

That makes perfect sense Mark, thanks ! I'll give it a go tomorrow.

Regards,

Todd.

 

[Fred Mellender]

You can create a Graphics on any object that inherits from Image, including
Bitmap.
Consult:
http://msdn.microsoft.com/library/d...y/en-us/vbcon/html/vbconintroductiontogdi.asp
which references the
Graphics.FromImage method.
Which is to say, you can use the GDI drawing routines with a Bitmap as the
underlying surface. Then you can copy that bitmap anywhere you wish.

On the other hand, it would seem that you could just redraw the graph
whenever the Paint event was raised on the window from which you called the
CreateGraphics method. I.E. put the logic that creates the Graphics, and
which draws the graph all in one method, and invoke that method in the
handler for the Paint event for the control that holds the graph. Then when
your popup moves off the graph's window, the Paint event will trigger the
redrawing of the graph. That is the usual way to handle the situation, I
believe. No Bitmap needed.

 

[Bob Powell [MVP]]

Firstly, drawing the image property contents of a picture box to the picture
box is nonsensical because that's what it does anyway. If you need a custom
drawing solution for images inherit from control and lose the PictureBox
baggage.

Secondly, you should never render anthing using CreateGraphics. See the #1
most asked GDI+ FAQ question for why.

--
Bob Powell [MVP]
Visual C#, System.Drawing

Ramuseco Limited .NET consulting
http://www.ramuseco.com

Find great Windows Forms articles in Windows Forms Tips and Tricks
http://www.bobpowell.net/tipstricks.htm

Answer those GDI+ questions with the GDI+ FAQ
http://www.bobpowell.net/faqmain.htm

All new articles provide code in C# and VB.NET.
Subscribe to the RSS feeds provided and never miss a new article.

 

[news]

Hi Fred,

I just worry that it will be too slow to redraw the graph.

Ive solved it now using Marks suggestion above,

Thanks for your post

Todd.

 

[news]

err, thanks for your reply Bob.

Todd.

Firstly, drawing the image property contents of a picture box to the
picture box is nonsensical because that's what it does anyway. If you need
a custom drawing solution for images inherit from control and lose the
PictureBox baggage.

Secondly, you should never render anthing using CreateGraphics. See the #1
most asked GDI+ FAQ question for why.

--
Bob Powell [MVP]
Visual C#, System.Drawing

Ramuseco Limited .NET consulting
http://www.ramuseco.com

Find great Windows Forms articles in Windows Forms Tips and Tricks
http://www.bobpowell.net/tipstricks.htm

Answer those GDI+ questions with the GDI+ FAQ
http://www.bobpowell.net/faqmain.htm

All new articles provide code in C# and VB.NET.
Subscribe to the RSS feeds provided and never miss a new article.

 

[news]

Yep, thanks Mark, got it working in under 5mins using your suggestion.

Im new to C# and the GDI+ and get lost in the functions sometimes...

Thanks again for the quick reply

Todd.