I have a Graphics object and a Panel. The Graphics object is instantiated with a Handler from the Panel. Then, the Panel is updated with the Paint action. Inside the Paint action, the Graphics object is used to paint. Sometimes through out the code I use the Invalidate() to update the panel.
I want to save the content of the Graphics object or the content of the Panel into a file. Whenever I try to do it, the image file is created, but blank.
Here are some snippets of the code:
I initiate Graphics object as a class variable:
Graphics GD_LD;
Then in the constructor I use the following to instantiate the object using the panel handler:
GD_LD = Graphics.FromHwnd(panelDrawLD.Handle);
Then I have the drawing function that is used on the Paint action of the Panel, were I use the Graphics object to make the all the drawings:
private void panelDrawLD_Paint(object sender, PaintEventArgs e)
{
..... some code ....
//Code example
GD_LD.FillPolygon(blackBrush, getPoints(min, sizeGP, scaleX, scaleY));
GD_LD.FillPolygon(blackBrush, getPoints(max, sizeGP, scaleX, scaleY));
..... some code ....
}
The above works fine to draw in the Panel and keep it always with the drawing.
The issue is when trying to save the Panel to a Image file:
Bitmap I_LD = new Bitmap(panelDrawLD.Size.Width, panelDrawLD.Size.Height);
panelDrawLD.DrawToBitmap(I_LD, new Rectangle(0,0, panelDrawLD.Size.Width, panelDrawLD.Size.Height));
I_LD.Save(tempPath + "I_LD.bmp",ImageFormat.Bmp);
The image file is created but without content. Just blank.
I saw some threads about this subject, but I could not adapt it to my situation.
What am I doing wrong? What's a possible solution?
What you really should be doing, is refactoring your Paint event in to a subroutine that takes a Graphics object as an argument called target. Do all your drawing against target. Then you can call that and pass e.Graphics from panelDrawLD_Paint, and call it from your other function with a Graphics you create with Graphics.FromImage(I_LD).
Also, if you create a Graphics (or any other GDI object), you MUST destroy it, or you will get a memory leak.
Like this:
private void panelDrawLD_Paint(object sender, PaintEventArgs e)
{
//e.Graphics does NOT need to be disposed of because *we* did not create it, it was passed to us by the control its self.
DrawStuff(e.Graphics);
}
private void Save()
{
// I_LD, and g are both GDI objects that *we* created in code, and must be disposed of. The "using" block will automatically call .Dispose() on the object when it goes out of scope.
using (Bitmap I_LD = new Bitmap(panelDrawLD.Size.Width, panelDrawLD.Size.Height))
{
using (Graphics g = Graphics.FromImage(I_LD))
{
DrawStuff(g);
}
I_LD.Save(tempPath + "I_LD.bmp", ImageFormat.Bmp);
}
}
private void DrawStuff(Graphics target)
{
//Code example
target.FillPolygon(blackBrush, getPoints(min, sizeGP, scaleX, scaleY));
target.FillPolygon(blackBrush, getPoints(max, sizeGP, scaleX, scaleY));
}
Related
in a UserControl I have a PictureBox and some other controls. For the user control which contains this picturebox named as Graph I have a method to draw a curve on this picture box:
//Method to draw X and Y axis on the graph
private bool DrawAxis(PaintEventArgs e)
{
var g = e.Graphics;
g.DrawLine(_penAxisMain, (float)(Graph.Bounds.Width / 2), 0, (float)(Graph.Bounds.Width / 2), (float)Bounds.Height);
g.DrawLine(_penAxisMain, 0, (float)(Graph.Bounds.Height / 2), Graph.Bounds.Width, (float)(Graph.Bounds.Height / 2));
return true;
}
//Painting the Graph
private void Graph_Paint(object sender, PaintEventArgs e)
{
base.OnPaint(e);
DrawAxis(e);
}
//Public method to draw curve on picturebox
public void DrawData(PointF[] points)
{
var bmp = Graph.Image;
var g = Graphics.FromImage(bmp);
g.DrawCurve(_penAxisMain, points);
Graph.Image = bmp;
g.Dispose();
}
When application starts, the axis are drawn. but when I call the DrawData method I get the exception that says bmp is null. What can be the problem?
I also want to be able to call DrawData multiple times to show multiple curves when user clicks some buttons. What is the best way to achive this?
Thanks
You never assigned Image, right? If you want to draw on a PictureBox’ image you need to create this image first by assigning it a bitmap with the dimensions of the PictureBox:
Graph.Image = new System.Drawing.Bitmap(Graph.Width, Graph.Height);
You only need to do this once, the image can then be reused if you want to redraw whatever’s on there.
You can then subsequently use this image for drawing. For more information, refer to the documentation.
By the way, this is totally independent from drawing on the PictureBox in the Paint event handler. The latter draws on the control directly, while the Image serves as a backbuffer which is painted on the control automatically (but you do need to invoke Invalidate to trigger a redraw, after drawing on the backbuffer).
Furthermore, it makes no sense to re-assign the bitmap to the PictureBox.Image property after drawing. The operation is meaningless.
Something else, since the Graphics object is disposable, you should put it in a using block rather than disposing it manually. This guarantees correct disposing in the face of exceptions:
public void DrawData(PointF[] points)
{
var bmp = Graph.Image;
using(var g = Graphics.FromImage(bmp)) {
// Probably necessary for you:
g.Clear();
g.DrawCurve(_penAxisMain, points);
}
Graph.Invalidate(); // Trigger redraw of the control.
}
You should consider this as a fixed pattern.
I'm writing a plugin for a trading software (C#, winforms, .NET 3.5) and I'd like to draw a crosshair cursor over a panel (let's say ChartPanel) which contains data that might be expensive to paint. What I've done so far is:
I added a CursorControl to the panel
this CursorControl is positioned over the main drawing panel so that it covers it's entire area
it's Enabled = false so that all input events are passed to the parent
ChartPanel
it's Paint method is implemented so that it draws lines from top to bottom and from left to right at current mouse position
When MouseMove event is fired, I have two possibilities:
A) Call ChartPanel.Invalidate(), but as I said, the underlying data may be expensive to paint and this would cause everything to redraw everytime I move a mouse, which is wrong (but it is the only way I can make this work now)
B) Call CursorControl.Invalidate() and before the cursor is drawn I would take a snapshot of currently drawn data and keep it as a background for the cursor that would be just restored everytime the cursor needs to be repainted ... the problem with this is ... I don't know how to do that.
2.B. Would mean to:
Turn existing Graphics object into Bitmap (it (the Graphics) is given to me through Paint method and I have to paint at it, so I just can't create a new Graphics object ... maybe I get it wrong, but that's the way I understand it)
before the crosshair is painted, restore the Graphics contents from the Bitmap and repaint the crosshair
I can't control the process of painting the expensive data. I can just access my CursorControl and it's methods that are called through the API.
So is there any way to store existing Graphics contents into Bitmap and restore it later? Or is there any better way to solve this problem?
RESOLVED: So after many hours of trial and error I came up with a working solution. There are many issues with the software I use that can't be discussed generally, but the main principles are clear:
existing Graphics with already painted stuff can't be converted to Bitmap directly, instead I had to use panel.DrawToBitmap method first mentioned in #Gusman's answer. I knew about it, I wanted to avoid it, but in the end I had to accept, because it seems to be the only way
also I wanted to avoid double drawing of every frame, so the first crosshair paint is always drawn directly to the ChartPanel. After the mouse moves without changing the chart image I take a snapshow through DrawToBitmap and proceed as described in chosen answer.
The control has to be Opaque (not enabled Transparent background) so that refreshing it doesn't call Paint on it's parent controls (which would cause the whole chart to repaint)
I still experience occasional flicker every few seconds or so, but I guess I can figure that out somehow. Although I picked Gusman's answer, I would like to thank everyone involved, as I used many other tricks mentioned in other answers, like the Panel.BackgroundImage, use of Plot() method instead of Paint() to lock the image, etc.
This can be done in several ways, always storing the graphics as a Bitmap. The most direct and efficient way is to let the Panel do all the work for you.
Here is the idea: Most winforms Controls have a two-layered display.
In the case of a Panel the two layers are its BackgroundImage and its Control surface.
The same is true for many other controls, like Label, CheckBox, RadioButton or Button.
(One interesting exception is PictureBox, which in addition has an (Foreground) Image. )
So we can move the expensive stuff into the BackgroundImage and draw the crosshair on the surcafe.
In our case, the Panel, all nice extras are in place and you could pick all values for the BackgroundImageLayout property, including Tile, Stretch, Center or Zoom. We choose None.
Now we add one flag to your project:
bool panelLocked = false;
and a function to set it as needed:
void lockPanel( bool lockIt)
{
if (lockIt)
{
Bitmap bmp = new Bitmap(panel1.ClientSize.Width, panel1.ClientSize.Width);
panel1.DrawToBitmap(bmp, panel1.ClientRectangle);
panel1.BackgroundImage = bmp;
}
else
{
if (panel1.BackgroundImage != null)
panel1.BackgroundImage.Dispose();
panel1.BackgroundImage = null;
}
panelLocked = lockIt;
}
Here you can see the magic at work: Before we actually lock the Panel from doing the expensive stuff, we tell it to create a snapshot of its graphics and put it into the BackgroundImage..
Now we need to use the flag to control the Paint event:
private void panel1_Paint(object sender, PaintEventArgs e)
{
Size size = panel1.ClientSize;
if (panelLocked)
{
// draw a full size cross-hair cursor over the whole Panel
// change this to suit your own needs!
e.Graphics.DrawLine(Pens.Red, 0, mouseCursor.Y, size.Width - 1, mouseCursor.Y);
e.Graphics.DrawLine(Pens.Red, mouseCursor.X, 0, mouseCursor.X, size.Height);
}
// expensive drawing, you insert your own stuff here..
else
{
List<Pen> pens = new List<Pen>();
for (int i = 0; i < 111; i++)
pens.Add(new Pen(Color.FromArgb(R.Next(111),
R.Next(111), R.Next(111), R.Next(111)), R.Next(5) / 2f));
for (int i = 0; i < 11111; i++)
e.Graphics.DrawEllipse(pens[R.Next(pens.Count)], R.Next(211),
R.Next(211), 1 + R.Next(11), 1 + R.Next(11));
}
}
Finally we script the MouseMove of the Panel:
private void panel1_MouseMove(object sender, MouseEventArgs e)
{
mouseCursor = e.Location;
if (panelLocked) panel1.Invalidate();
}
using a second class level variable:
Point mouseCursor = Point.Empty;
You call lockPanel(true) or lockPanel(false) as needed..
If you implement this directly you will notice some flicker. This goes away if you use a double-buffered Panel:
class DrawPanel : Panel
{
public DrawPanel() { this.DoubleBuffered = true; }
}
This moves the crosshair over the Panels in a perfectly smooth way. You may want to turn on & off the Mouse cursor upon MouseLeave and MouseEnter..
Why don't you clone all the graphics in the ChartPanel over your CursorControl?
All the code here must be placed inside your CursorControl.
First, create a property which will hold a reference to the chart and hook to it's paint event, something like this:
ChartPanel panel;
public ChartPanel Panel
{
get{ return panel; }
set{
if(panel != null)
panel.Paint -= CloneAspect;
panel = value;
panel.Paint += CloneAspect;
}
}
Now define the CloneAspect function which will render the control's appearance to a bitmap whenever a Paint opperation has been done in the Chart panel:
Bitmap aspect;
void CloneAspect(object sender, PaintEventArgs e)
{
if(aspect == null || aspect.Width != panel.Width || aspect.Height != panel.Height)
{
if(aspect != null)
aspect.Dispose();
aspect = new Bitmap(panel.Width, panel.Height, System.Drawing.Imaging.PixelFormat.Format32bppPArgb);
}
panel.DrawToBitmap(aspect, new Rectangle(0,0, panel.Width, panel.Height);
}
Then in the OnPaint overriden method do this:
public override void OnPaint(PaintEventArgs e)
{
e.Graphics.DrawImage(aspect);
//Now draw the cursor
(...)
}
And finally wherever you create the chart and the customcursor you do:
CursorControl.Panel = ChartPanel;
And voila, you can redraw as many times you need without recalculating the chart's content.
Cheers.
I simulate map navigation and draw generated part of the map on a panel. Since image is flickering I have to use double buffering.
Here's my Panel code:
public class MapPanel : System.Windows.Forms.Panel
{
public MapPanel()
{
DoubleBuffered = true;
ResizeRedraw = true;
}
}
And I have the following method:
public void panelMap_Paint(object sender, PaintEventArgs e)
{
using (Graphics g = e.Graphics)
{
g.DrawImage(mapController.GetCurrentMap(), 0, 0, panelMap.Width, panelMap.Height);
}
}
I'm not calling this method. I have the following code in .Designer.cs:
this.panelMap.Paint += new PaintEventHandler(this.panelMap_Paint);
And call Invalidate() in MouseMove. I'm sure that this event occurs, I've checked it. Everything seems to be correct.
And then the image is not drawing. I mean, the panel is empty and seems to be transparent or colored in default control color. However, if I turn double buffering off, the image is properly drawn, but, obviously, it's flickering. Could you help me?
Remove the using statement. You are disposing of the Graphics object before it is used to draw to the screen.
As mentioned, you should also remove the Invalidate() call from the paint method.
public void panelMap_Paint(object sender, PaintEventArgs e)
{
var g = e.Graphics;
g.DrawImage(mapController.GetCurrentMap(), 0, 0, panelMap.Width, panelMap.Height);
}
You should comment out the following code
//panelMap.Invalidate();
According to MSDN
Invalidates the entire surface of the control and causes the control to be
redrawn.
I have a User Control which contains a panel by name of panel1. there is a instruction in the panel1_paint which draws some lines on the panel,I am going to execute paint event in a windows form by line below :
NOTE : DrawLines has defined in UserControl1.CS
public void DrawLines()
{
...
...
panel1.Invalidate();
}
I don't know why this won't run , maybe it draws line and then panel makes a refresh and this make the panel to be cleared.
So I changed my code to this :
public void DrawLines()
{
...
...
panel1_Paint(this, new PaintEventArgs(panel1.CreateGraphics(),
panel1.ClientRectangle));
}
This works nice.it draws some lines in the panel, now the main part is :
there are some objects that they will create at run time on the panel as children . I want to move them over the panel (for example suppose there are fire particles) . so when I move (animate) them by timer , the lines which drawn by the e.Graphics of the Paint Event will be cleared and removed if any of those objects(particles) on the panel move over them.
So How can I avoid this ?! Is there any problem with my Invalidation ?
How can I have both, lines and moving particles on the panel ?
panel has done the graphics , but why by moving objects on it, the graphics will removed?
Here's how to use the supplied Graphics in the Paint() event:
private void panel1_Paint(object sender, PaintEventArgs e)
{
Graphics G = e.Graphics;
// ... use "G" to draw with ...
G.DrawLine(Pens.Black, 0, 0, panel1.Width, panel1.Height);
}
Then you can simply use:
panel1.Invalidate();
in a UserControl I have a PictureBox and some other controls. For the user control which contains this picturebox named as Graph I have a method to draw a curve on this picture box:
//Method to draw X and Y axis on the graph
private bool DrawAxis(PaintEventArgs e)
{
var g = e.Graphics;
g.DrawLine(_penAxisMain, (float)(Graph.Bounds.Width / 2), 0, (float)(Graph.Bounds.Width / 2), (float)Bounds.Height);
g.DrawLine(_penAxisMain, 0, (float)(Graph.Bounds.Height / 2), Graph.Bounds.Width, (float)(Graph.Bounds.Height / 2));
return true;
}
//Painting the Graph
private void Graph_Paint(object sender, PaintEventArgs e)
{
base.OnPaint(e);
DrawAxis(e);
}
//Public method to draw curve on picturebox
public void DrawData(PointF[] points)
{
var bmp = Graph.Image;
var g = Graphics.FromImage(bmp);
g.DrawCurve(_penAxisMain, points);
Graph.Image = bmp;
g.Dispose();
}
When application starts, the axis are drawn. but when I call the DrawData method I get the exception that says bmp is null. What can be the problem?
I also want to be able to call DrawData multiple times to show multiple curves when user clicks some buttons. What is the best way to achive this?
Thanks
You never assigned Image, right? If you want to draw on a PictureBox’ image you need to create this image first by assigning it a bitmap with the dimensions of the PictureBox:
Graph.Image = new System.Drawing.Bitmap(Graph.Width, Graph.Height);
You only need to do this once, the image can then be reused if you want to redraw whatever’s on there.
You can then subsequently use this image for drawing. For more information, refer to the documentation.
By the way, this is totally independent from drawing on the PictureBox in the Paint event handler. The latter draws on the control directly, while the Image serves as a backbuffer which is painted on the control automatically (but you do need to invoke Invalidate to trigger a redraw, after drawing on the backbuffer).
Furthermore, it makes no sense to re-assign the bitmap to the PictureBox.Image property after drawing. The operation is meaningless.
Something else, since the Graphics object is disposable, you should put it in a using block rather than disposing it manually. This guarantees correct disposing in the face of exceptions:
public void DrawData(PointF[] points)
{
var bmp = Graph.Image;
using(var g = Graphics.FromImage(bmp)) {
// Probably necessary for you:
g.Clear();
g.DrawCurve(_penAxisMain, points);
}
Graph.Invalidate(); // Trigger redraw of the control.
}
You should consider this as a fixed pattern.