I have a problem on creating bitmap image out of my winform application.
Situation:
I have a UserControl named as "CanvasControl" that accepts OnPaint method acting as canvas for my Draw Pad application. Inside this user control I have a function "PrintCanvas()" that will create a screenshot image of the UserControl into PNG file. Below is the PrintCanvas() function:
public void PrintCanvas(string filename = "sample.png")
{
Graphics g = this.CreateGraphics();
//new bitmap object to save the image
Bitmap bmp = new Bitmap(this.Width, this.Height);
//Drawing control to the bitmap
this.DrawToBitmap(bmp, new Rectangle(0, 0, this.Width, this.Height));
bmp.Save(Application.StartupPath +
#"\ExperimentFiles\Experiment1" + filename, ImageFormat.Png);
bmp.Dispose();
}
This user control (CanvasControl) is called out inside my main form where user will draw something and have an option to save afterwards using a save button. The save button will call out the "PrintCanvas()" function of the UserControl.
I get the output image file as expected, but the problem is it was a blank image.
What I have tried so far:
To test that it is not a syntax issue, I tried to transfer the PrintCanvas() function into my main form and surprisingly I get an image of the whole main form on file but the UserControl is not visible there.
Is there any other setup i missed out to make a winform UserControl printable?
UPDATE: (DRAWING ROUTINES)
User control acting as canvas - code here
The code in the question gave a first hint but the code in the link showed the source of the problem: You use a 'wrong' instance of the Graphics object for drawing:
protected override void OnPaint(PaintEventArgs e)
{
// If there is an image and it has a location,
// paint it when the Form is repainted.
Graphics graphics = this.CreateGraphics();
..
This is one of the most common mistakes with winforms graphics! Never use CreateGraphics ! You always should draw onto the control surface with the Graphics object in a Paint or DrawXXX event. These events have a parameter e.Graphics which is the only one that can draw persistent graphics.
Persistent means that it will always be refreshed when necessary, not just when you trigger it. This is a nasty error because everything seems to work until you come upon a situation when an outside event makes redrawing necessary:
Minimizing and then maximizing the form
Moving it off the screen and back again
Calling DrawToBitmap
...
Note that all will only really work if you use the valid and current Graphics object from the PaintEventArgs e parameter.
So, the solution is simple:
protected override void OnPaint(PaintEventArgs e)
{
// If there is an image and it has a location,
// paint it when the Form is repainted.
Graphics graphics = e.Graphics(); // << === !!
..
But what is the CreateGraphics good for? It is only good for luring newbies into that error??
Not quite; here are some uses for it:
Drawing non-persistent graphics like a rubber-band rectangle or a special mouse cursor
Measuring text sizes without actually drawing it with a TextRenderer or the MeasureString method
Querying the screen or Bitmap resolution with Graphics.DpiX/Y
and probably some others I can't think of at the moment..
So for normal drawing onto controls always use the e.Grapahics object! You can pass it on to subroutines to make the code more structured, but do not try to cache it; it needs to be current!
Related
I am working with a fingerprint module and am able to capture and display the output in a picture box (C#). Now picture.Image is null even though picturebox displays an image. So I am trying to save the picturebox image as bmp and then assign that bmp to the same picturebox so that Picturebox.image is not null.
Here is the code :
Bitmap bmp = new Bitmap(picFP.width, picFP.height);
picFP.DrawToBitmap(bmp, picFP.ClientRectangle);
bmp.Save("path", Imageformat.bmp);
picFP.image = bmp;
Here bitmap image saved is blank. What can be the problem?
A PictureBox has three layers it can display and PictureBox.DrawToBitmap will put all three things into the Bitmap:
The BackgroundImage
The Image
Any graphics created in or from the Paint event
If your bitmap comes out black then you have none of the three, or the last you have is all black.
From your description it seems as if you can display the image in the PictureBox.
So I assume that you don't display it in the right way, probably you do it like this:
using (Graphics G = picFP.CreateGraphics())
G.DrawImage(yourCapturedImage, ..)
This will not work as it only creates non-persistent graphics. These go away with e.g. each minimize-restore cycle and are not called from the DrawToBitmap call
If you really want to draw it onto the PB's surface use the Paint event! But the more natural choice would be to set the PB's Image directly:
picFP.Image = yourCapturedImage;
Update 1 As you now reveal that you don't display it yourself but simply give the control handle to the external code objNitgen=picFP.Handle; the same applies: It is that Nitgen draws only onto the surface and the result is non-persistent.
In this case the remedy is either
Taking a screenshot of the result and then work from that. Here is a post that shows you how to capture a control via screenshot..
Or you may want to check if Nitgen will draw into a bitmap directly..
For this you should be to pass it not a handle to the PictureBox but to a Bitmap instead:
private void button_Click(object sender, EventArgs e)
{
Bitmap bmp = new Bitmap(picFP.ClientSize.Width, picFP.ClientSize.Height);
Graphics G = Graphics.FromImage(bmp);
IntPtr dc= G.GetHdc();
objNitgen = dc;
objNitgen.capture();
G.ReleaseHdc(dc);
pictureBox1.Image = bmp; // now display..
bmp.Save(yourfilename); // .. and/or save
}
Update 2
You noted in a comment that doing a manual screenshot also does not capture the image; so it seems the control handle is only used to overlay it with the image much like video overlays do; if this is the case I doubt you can get at the image without using other, more fitting Nitgen SDK methods.
I've written a Windows Forms app where I do custom drawing on a Panel using Control.CreateGraphics(). Here's what my Form looks like at startup:
The custom drawing is performed on the top panel in the Click event handler of the "Draw!" button. Here's my button click handler:
private void drawButton_Click(object sender, EventArgs e)
{
using (Graphics g = drawPanel.CreateGraphics())
{
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
g.Clear(Color.White);
Size size = drawPanel.ClientSize;
Rectangle bounds = drawPanel.ClientRectangle;
bounds.Inflate(-10, -10);
g.FillEllipse(Brushes.LightGreen, bounds);
g.DrawEllipse(Pens.Black, bounds);
}
}
After a click on drawButton, the form looks like this:
Success!
But when I shrink the form by dragging a corner...
...and expand it back to its original size,
part of what I drew is gone!
This also happens when I drag part of the window offscreen...
...and drag it back onscreen:
If I minimize the window and restore it, the whole image is erased:
What is causing this? How can I make it so the graphics I draw are persistent?
Note: I've created this self-answered question so I have a canonical Q/A to direct users to, as this is a common scenario that's hard to search for if you don't already know the cause of the problem.
TL;DR:
Don't do your drawing in response to a one-time UI event with Control.CreateGraphics. Instead, register a Paint event handler for the control on which you want to paint, and do your drawing with the Graphics object passed via the PaintEventArgs.
If you want to paint only after a button click (for example), in your Click handler, set a boolean flag indicating that the button has been clicked and then call Control.Invalidate(). Then do your rendering conditionally in the Paint handler.
Finally, if your control's contents should change with the size of the control, register a Resize event handler and call Invalidate() there too.
Example code:
private bool _doCustomDrawing = false;
private void drawPanel_Paint(object sender, PaintEventArgs e)
{
if (_doCustomDrawing)
{
Graphics g = e.Graphics;
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
g.Clear(Color.White);
Size size = drawPanel.ClientSize;
Rectangle bounds = drawPanel.ClientRectangle;
bounds.Inflate(-10, -10);
g.FillEllipse(Brushes.LightGreen, bounds);
g.DrawEllipse(Pens.Black, bounds);
}
}
private void drawButton_Click(object sender, EventArgs e)
{
_doCustomDrawing = true;
drawPanel.Invalidate();
}
private void drawPanel_Resize(object sender, EventArgs e)
{
drawPanel.Invalidate();
}
But why? What was I doing wrong, and how does this fix it?
Take a look at the documentation for Control.CreateGraphics:
The Graphics object that you retrieve through the CreateGraphics method should not normally be retained after the current Windows message has been processed, because anything painted with that object will be erased with the next WM_PAINT message.
Windows doesn't take responsibility for retaining the graphics you draw to your Control. Rather, it identifies situations in which your control will require a repaint and informs it with a WM_PAINT message. Then it's up to your control to repaint itself. This happens in the OnPaint method, which you can override if you subclass Control or one of its subclasses. If you're not subclassing, you can still do custom drawing by handling the public Paint event, which a control will fire near the end of its OnPaint method. This is where you want to hook in, to make sure your graphics get redrawn every time the Control is told to repaint. Otherwise, part or all of your control will be painted over to the control's default appearance.
Repainting happens when all or part of a control is invalidated. You can invalidate the entire control, requesting a full repaint, by calling Control.Invalidate(). Other situations may require only a partial repaint. If Windows determines that only part of a Control needs to be repainted, the PaintEventArgs you receive will have a non-empty ClipRegion. In this situation, your drawing will only affect the area in the ClipRegion, even if you try to draw to areas outside that region. This is why the call to drawPanel.Invalidate() was required in the above example. Because the appearance of drawPanel needs to change with the size of the control and only the new parts of the control are invalidated when the window is expanded, it's necessary to request a full repaint with each resize.
I wasn't able to find an answer for this:
I have a background image on my form that I want to remain visible even when the system is on High Contrast mode. Is there code that can be entered that overrides the HC mode?
I've tried this on the Form Load event but no luck- no definition for graphics. (Not sure this would even be a viable solution):
OnPaint: e.Graphics.DrawImage(new Bitmap(BackgroundImage), 0, 0);
Aside from creating a PictureBox across my form and putting the image that way, does anyone know of a way to show the BG image of the form always?
Override the OnPaintBackground method:
protected override void OnPaintBackground(PaintEventArgs e)
{
e.Graphics.DrawImage(new Bitmap(BackgroundImage), e.ClipRectangle);
}
This DrawImage overload will stretch the image to fit the rectangle. If the ClipRectangle doesn't work (sorry, I can't test this right now!), create a new Rectangle with the background dimensions
I have a winform c# app.
I am using Emgu for comparing the motion differences between 2 images.
I impose the changes detected onto the 1st image so in affect the first image now looks identical to the second image.
I am overriding the onpaint event of a user control to draw the image. I have to Invalidate the usercontrol to force the onpaint event.
This works well but the memory still 'spikes' a bit. Is there a way to invalidate only the pixels that have changed - like regions for instance?
This is my current code:
protected override void OnPaint(PaintEventArgs pe)
{
Graphics g = pe.Graphics;
if (CurrentFrame != null)
{
pe.Graphics.DrawImageUnscaled(CurrentFrame, 0, 0);
}
}
The CurrentFrame is a static Bitmap
Thanks
I'm trying to build my own custom control for a windows forms application in C#.Net. Currently I paint some rectangles and other graphic elements using the paint event.
When I now resize the app form to fit the desktop size, all elements are repainted (which is exactly the behaviour I need) but the old one's are shown in the background.
Here's what I'm doing by now:
Pen penDefaultBorder = new Pen(Color.Wheat, 1);
int margin = 5;
private void CustomControl_Paint(object sender, PaintEventArgs e) {
CustomControl calendar = (CustomControl)sender;
Graphics graphics = e.Graphics;
graphics.Clear(Color.WhiteSmoke);
graphics.DrawRectangle(penDefaultBorder, margin, margin, calendar.Width - margin * 2, calendar.Height - margin * 2);
//...
}
Neither the graphics.Clear, nor adding a graphics.FillRectangle(...) will hide the old rectangle from the surface.
Ideas? Thank you all.
Paint events usually don't request an update for the entire canvas, just the area specified in the PaintEventArgs. I'm guessing what's happening is that only the newly-exposed regions of the canvas are being passed in the PaintEventArgs.
This one of the reasons that you shouldn't do any rendering in the Paint event. You should render to an offscreen bitmap - a buffer - and copy from that buffer to the control's canvas in the Paint event.
Searching for "double buffering" here or on Google will give you many examples of the technique.
Have you tried .Invalidate() to cause the form to redraw?