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How to use Control.DrawToBitmap to render a Form into a Bitmap without its decorations (titlebar, border)? [duplicate]

This question already has an answer here:
Take screenshot from window content (without border)
(1 answer)
Closed 4 years ago.
I have a Form and in it an Overlay control (transparent gray backcolor with White text over "Drop here..." and an icon) that is visible only when a file is dragged over the Form. The Overlay is made transparent by drawing the control in its back on it and then filling over with transparent gray (ARGB). The method Works very well when the Overlay should be over a Control that is not a Form, but when I use Control.DrawToBitmap to render a Form, not an usual Control, it also renders the title bar and border.

Form.DrawToBitmap draws the whole form including non-client area. You can use BitBlt. The BitBlt function performs a bit-block transfer of the color data corresponding to a rectangle of pixels from the specified source device context into a destination device context.
const int SRCCOPY = 0xCC0020;
[DllImport("gdi32.dll")]
static extern int BitBlt(IntPtr hdc, int x, int y, int cx, int cy,
IntPtr hdcSrc, int x1, int y1, int rop);
Image PrintClientRectangleToImage()
{
var bmp = new Bitmap(ClientSize.Width, ClientSize.Height);
using (var bmpGraphics = Graphics.FromImage(bmp))
{
var bmpDC = bmpGraphics.GetHdc();
using (Graphics formGraphics = Graphics.FromHwnd(this.Handle))
{
var formDC = formGraphics.GetHdc();
BitBlt(bmpDC, 0, 0, ClientSize.Width, ClientSize.Height, formDC, 0, 0, SRCCOPY);
formGraphics.ReleaseHdc(formDC);
}
bmpGraphics.ReleaseHdc(bmpDC);
}
return bmp;
}

The Control.DrawToBitmap method always return a Bitmap drawn from the upper-left corner of the control, even if you pass the method a Rectangle with specific bounds.
Here, the ClientRectangle portion of a Form is translated using the Size of its Bounds.
Note that, if your application is not DPIAware, you might get wrong measures from all the methods that return a Point or a Rectangle. Non-DPIAware Windows API included.
If you need to save the resulting Bitmap, use PNG as the destination format: its loss-less compression is better suited for this kind of rendering.
Call this method with the ClientAreaOnly argument set to true to have it return a Bitmap of the ClientArea only.
public Bitmap FormScreenShot(Form form, bool clientAreaOnly)
{
var fullSizeBitmap = new Bitmap(form.Width, form.Height, PixelFormat.Format32bppArgb);
// .Net 4.7+
fullSizeBitmap.SetResolution(form.DeviceDpi, form.DeviceDpi);
form.DrawToBitmap(fullSizeBitmap, new Rectangle(Point.Empty, form.Size));
if (!clientAreaOnly) return fullSizeBitmap;
Point p = form.PointToScreen(Point.Empty);
var clientRect =
new Rectangle(new Point(p.X - form.Bounds.X, p.Y - form.Bounds.Y), form.ClientSize);
var clientAreaBitmap = fullSizeBitmap.Clone(clientRect, PixelFormat.Format32bppArgb);
fullSizeBitmap.Dispose();
return clientAreaBitmap;
}

You could render the whole form and then take only the part you need with Bitmap.Clone(). Here you have explained how to do it.

Screenshot method generates black images

After failing to use the control.drawtobitmap in c#, my second option was to take screenshots of the desktop and crop out the desired sections.
My hiccup shows up once i switch user accounts, although the program does not crash, once the user is switched the program generates pure black images only.
I used this code as a reference:
WebBrowser.DrawToBitmap() or other methods?
I guess logically this makes sense as this would help windows save resources.
What options/ solutions do i have in my situation?
Edit 1
made a modification to the code for testing:
int c = 0;
while (true)
{
try
{
c++;
Rectangle formBounds = this.Bounds;
Bitmap bmp = new Bitmap(formBounds.Width, formBounds.Height);
using (Graphics g = Graphics.FromImage(bmp))
g.CopyFromScreen(formBounds.Location, Point.Empty, formBounds.Size);
bmp.Save("picture" + c.ToString() + ".jpg");
Thread.Sleep(5000);
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
this works perfectly while on the user account, but as soon as i switch users, it returns the exception: The handle is invalid.
Any ideas?
Edit 2:
The bug in DrawToBitmap is not exactly random...
if i used the code you supplied:
Bitmap bmp = new Bitmap(this.ClientRectangle.Width, this.ClientRectangle.Height);
this.DrawToBitmap(bmp, this.ClientRectangle);
bmp.Save(".\\picture.jpg");
it works perfectly, example: http://oi61.tinypic.com/1z23ynp.jpg
However, the moment i right-click on the web-browser control, DrawToBitmap will return a blank image.
example: http://oi60.tinypic.com/9ay0yc.jpg
So i can easily overcome this bug by adding
((Control)webbrowser1).Enabled = false;
this makes any clicking impossible on the web-browser, but unfortunately to deactivate it would render my project useless as its main function is to emulate mouse clicks on a web-browser control.
although this might also be a problem if the window is hidden.
currently im looking at this post, where code is supplied to give you a window handle.
Simulate click into a hidden window
it seems it might be of some value... do have a look.

What were the problems you had with DrawToBitmap?
It works fine here, (W8.1, VS2013) even with a Webcontrol and also after switching users. (But see the edit at the end for the conditions!)
Bitmap bmp = new Bitmap(this.ClientRectangle.Width, this.ClientRectangle.Height);
this.DrawToBitmap(bmp, this.ClientRectangle);
// Clipboard.SetImage(bmp); for testing only
bmp.Dispose();
Here is code to take a screenshot of your window:
Rectangle formBounds = this.Bounds;
Bitmap bmp = new Bitmap(formBounds.Width, formBounds.Height );
using (Graphics g = Graphics.FromImage(bmp))
g.CopyFromScreen(formBounds.Location, Point.Empty, formBounds.Size);
//Clipboard.SetImage(bmp); for testing only
bmp.Dispose();
I can switch users like I want, the program keeps working.
BTW, the link you posted is really old, many things may have improved.
Edit:
With the updated question things are a lot clearer.
So you want to continuously get a screenshot of your program even when the user has changed, right?
and you want to display a WebControl, right?
A user can have three types of desktop: the logon/logoff screen, the screensaver screen and one or more normal desktop screen(s). But while the user is logged off he has no desktop screen at all.
Therefore the screenshot method will not work if the user has no active desktop, neither as g.CopyFromScreen, which will cause a GDI-error nor using a window handle like in the various solutions on the web, including the ones your link leads to. All these will, at best, show a blank or black screen.
So the DrawToBitmap method is the only one that works.
You wrote that it has random errors. That's not what I see.
The problems come in predictably when the user interacts with the WebBrowser in any way. This includes scrolling or clicking with or without navigation. After these interactions the WebBrowser will draw itself as an empty box until its URL is reloaded - not only refreshed - but really reloaded by webBrowser1.Uri = new Uri(uriPath). This can be done, see my other post
The WebBrowser also has another issue when doing a DrawToBitmap: It will fail (with the said empty box) for any pages that include an <input type="text" element. I'm not sure what's the best way to workaround this, let alone why it happends in the first place.. A screenshot method doesn't have that specific problem.
Edit 2:
The code the OP has dug up code which, using a call to PrintWindow, seems to solve all problems we had: It works while being logged off, works with Refeshing even after clicking in the WebBrowser and scrapes all pages, including those with textual input fields. Hoorah!
After cutting down the slack here is a version that can create a copy of the Form or just the WebBroser (or any other Control) with or without borders:
[DllImport("user32.dll")]
public static extern bool PrintWindow(IntPtr hwnd, IntPtr hdcBlt, uint nFlags);
public Bitmap CaptureWindow(Control ctl)
{
//Bitmap bmp = new Bitmap(ctl.Width, ctl.Height); // includes borders
Bitmap bmp = new Bitmap(ctl.ClientRectangle.Width, ctl.ClientRectangle.Height); // content only
using (Graphics graphics = Graphics.FromImage(bmp))
{
IntPtr hDC = graphics.GetHdc();
try { PrintWindow(ctl.Handle, hDC, (uint)0); }
finally { graphics.ReleaseHdc(hDC); }
}
return bmp;
}

Finally this code seems to work even when i have switched users.
Code to take screen shot of any unsaved Notepad process ("Untitled - Notepad")
private void Form1_Load(object sender, EventArgs e)
{
//loop for debugging
int c = 0;
while(true)
{
c++;
System.Drawing.Bitmap image = CaptureWindow(FindWindow(null, "Untitled - Notepad"));
image.Save(".\\picture"+c.ToString()+".jpg");
Thread.Sleep(5000);
}
}
[DllImport("user32.dll")]
public static extern bool PrintWindow(IntPtr hwnd, IntPtr hdcBlt, uint nFlags);
[DllImport("user32.dll")]
public static extern IntPtr GetWindowDC(IntPtr hWnd);
[DllImport("user32.dll", SetLastError = true)]
static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
public System.Drawing.Bitmap CaptureWindow(IntPtr hWnd)
{
System.Drawing.Rectangle rctForm = System.Drawing.Rectangle.Empty;
using (System.Drawing.Graphics grfx = System.Drawing.Graphics.FromHdc(GetWindowDC(hWnd)))
{
rctForm = System.Drawing.Rectangle.Round(grfx.VisibleClipBounds);
}
System.Drawing.Bitmap pImage = new System.Drawing.Bitmap(rctForm.Width, rctForm.Height);
System.Drawing.Graphics graphics = System.Drawing.Graphics.FromImage(pImage);
IntPtr hDC = graphics.GetHdc();
try
{
PrintWindow(hWnd, hDC, (uint)0);
}
finally
{
graphics.ReleaseHdc(hDC);
}
return pImage;
}
Note that the window may be hidden but it must still be maximized on the user account to get a complete screen shot.

Digital Rights Management may be stopping this, because Windows adds protection for digital media.
If, for example, you are attempting to create a screen capture of something in Media Player or Media Center using Microsoft's rendering of Graphics - yes, Microsoft is going to "protect you from any potential lawsuit."
Try this: Click "Print Screen" on your keyboard and then go into Microsoft Paint and try pasting your screen capture into it. Is anything there?

I faced with the same problem and I couldn't use CopyFromScreen method because my form with WebBrowser could be hidded. PrintWindow method also didn't work well generating images with black areas, especially when my MDI form partially covered by MDI parent form.
Finally I used OleDraw method as in this topic on SO, but integrated it in a class derived from WebBrowser. Basically, it just overrides standard control reaction to WM_PRINT message. This allows to do normal Control.DrawToBitmap not only for the WebBrowser, but for a form with WebBrowser in it as well. This also works if the form is hidden (covered by another form, including MDI parent form) and should work when user has locked session with Win+L (I haven't tested it).
public class WebBrowserEx : WebBrowser
{
private const uint DVASPECT_CONTENT = 1;
[DllImport("ole32.dll", PreserveSig = false)]
private static extern void OleDraw([MarshalAs(UnmanagedType.IUnknown)] object pUnk,
uint dwAspect,
IntPtr hdcDraw,
[In] ref System.Drawing.Rectangle lprcBounds
);
protected override void WndProc(ref Message m)
{
const int WM_PRINT = 0x0317;
switch (m.Msg)
{
case WM_PRINT:
Rectangle browserRect = new Rectangle(0, 0, this.Width, this.Height);
// Don't know why, but drawing with OleDraw directly on HDC from m.WParam.
// results in badly scaled (stretched) image of the browser.
// So, drawing to an intermediate bitmap first.
using (Bitmap browserBitmap = new Bitmap(browserRect.Width, browserRect.Height))
{
using (var graphics = Graphics.FromImage(browserBitmap))
{
var hdc = graphics.GetHdc();
OleDraw(this.ActiveXInstance, DVASPECT_CONTENT, hdc, ref browserRect);
graphics.ReleaseHdc(hdc);
}
using (var graphics = Graphics.FromHdc(m.WParam))
{
graphics.DrawImage(browserBitmap, Point.Empty);
}
}
// ignore default WndProc
return;
}
base.WndProc(ref m);
}
}

Detect game hack through screenshot analysis C#

I'm trying to write some code to detect a wallhack for a game.
Basically, some hacks exist which create a windows aero transparent window, and they draw the hack onto this external window, so it can't be detected by taking a screenshot of the game itself.
My approach at the moment is to -
1. take a screenshot of the game window.
2. take a screenshot of the windows desktop for the same coordinates.
3. perform image analysis to compare screenshot 1 to screenshot 2 to see if there is a difference.
My problem is that screenshot 1 and screenshot 2 are not performed simultaneously so new game frames can be drawn between the two screenshots, causing false positives when the images are compared.
I want to know if there is a way to coordinate the screenshots so they occur at exactly the same time ? or somehow stop the screen drawing any new frames until my screenshots are finished?
This is the code I use for taking screenshots.
Note, I have even tried to take the 2 screenshots in parallel by queuing two work items.
However, even this doesn't result in the screenshots happening at exactly the same time.
So I wonder if there is some way to stop any further updates to screen from the graphics card until my screenshots finish? Or any other way I can do this?
public void DoBitBlt(IntPtr dest, int width, int height, IntPtr src)
{
GDI32.BitBlt(dest, 0, 0, width, height, src, 0, 0, GDI32.SRCCOPY);
}
public struct Windows
{
public Bitmap window;
public Bitmap desktop;
}
public Windows CaptureWindows(IntPtr window, IntPtr desktop, User32.RECT coords)
{
Windows rslt = new Windows();
// get te hDC of the target window
IntPtr hdcSrcWindow = User32.GetWindowDC(window);
IntPtr hdcSrcDesktop = User32.GetWindowDC(desktop);
// get the size
int width = coords.right - coords.left;
int height = coords.bottom - coords.top;
// create a device context we can copy to
IntPtr hdcDestWindow = GDI32.CreateCompatibleDC(hdcSrcWindow);
IntPtr hdcDestDesktop = GDI32.CreateCompatibleDC(hdcSrcDesktop);
// create a bitmap we can copy it to,
// using GetDeviceCaps to get the width/height
IntPtr hBitmapWindow = GDI32.CreateCompatibleBitmap(hdcSrcWindow, width, height);
IntPtr hBitmapDesktop = GDI32.CreateCompatibleBitmap(hdcSrcDesktop, width, height);
// select the bitmap object
IntPtr hOldWindow = GDI32.SelectObject(hdcDestWindow, hBitmapWindow);
IntPtr hOldDesktop = GDI32.SelectObject(hdcDestDesktop, hBitmapDesktop);
// bitblt over
var handle1 = new ManualResetEvent(false);
var handle2 = new ManualResetEvent(false);
Action actionWindow = () => { try { DoBitBlt(hdcDestWindow, width, height, hdcSrcWindow); } finally { handle1.Set(); } };
Action actionDesktop = () => { try { DoBitBlt(hdcDestDesktop, width, height, hdcSrcDesktop); } finally { handle2.Set(); } };
ThreadPool.QueueUserWorkItem(x => actionWindow());
ThreadPool.QueueUserWorkItem(x => actionDesktop());
WaitHandle.WaitAll(new WaitHandle[] { handle1, handle2 });
rslt.window = Bitmap.FromHbitmap(hBitmapWindow);
rslt.desktop = Bitmap.FromHbitmap(hBitmapDesktop);
// restore selection
GDI32.SelectObject(hdcDestWindow, hOldWindow);
GDI32.SelectObject(hdcDestDesktop, hOldDesktop);
// clean up
GDI32.DeleteDC(hdcDestWindow);
GDI32.DeleteDC(hdcDestDesktop);
User32.ReleaseDC(window, hdcSrcWindow);
User32.ReleaseDC(desktop, hdcSrcDesktop);
// free up the Bitmap object
GDI32.DeleteObject(hBitmapWindow);
GDI32.DeleteObject(hBitmapDesktop);
return rslt;
}

You are not going to be able to have both screenshots simultaneously, unless you resource to some graphic accelarators, meaning that that will not work in every computer...
About stopping rendering, as it is a game, I think this is not so good idea... you want your game to run smoothly.
Instead I would like to suggest to store recently rendered images of your game in memory, and when you take the screenshot compare it to them. If you can add some visual clue to decide which of the recent frames to compare to then it will work much better, because otherwise you will have to compare the screenshot to all of them and that will certainly eat some CPU/GPU time.
Are you using GDI to render? if so, what you want is to store the frames of your game in DIBs (Device Independent Bitmaps) to be able to compare them.
As for the clue to decide which image to use, I would go for some sort of time representation on screen, maybe a single pixel that changes color. If so, you will read the color of that pixel, use it to find the right frame, and them proced to compare the whole picture.

How to redraw only a region of a layered window?

I have a layered window which is normally drawn this way:
private void SelectBitmap(Bitmap bitmap)
{
IntPtr screenDc = GetDC(IntPtr.Zero);
IntPtr memDc = CreateCompatibleDC(screenDc);
IntPtr hBitmap = IntPtr.Zero;
IntPtr hOldBitmap = IntPtr.Zero;
try
{
hBitmap = bitmap.GetHbitmap(Color.FromArgb(0));
hOldBitmap = SelectObject(memDc, hBitmap);
POINT sourceLocation = new POINT(0, 0);
BLENDFUNCTION blend = new BLENDFUNCTION();
blend.BlendOp = AC_SRC_OVER;
blend.BlendFlags = 0;
blend.SourceConstantAlpha = 255;
blend.AlphaFormat = AC_SRC_ALPHA;
SIZE newSize = new SIZE(bitmap.Width, bitmap.Height);
POINT newLocation = new POINT(Location.X, Location.Y);
UpdateLayeredWindow(Handle, screenDc,
ref newLocation, ref newSize,
memDc,
ref sourceLocation, 0,
ref blend,
ULW_ALPHA);
}
finally
{
ReleaseDC(IntPtr.Zero, screenDc);
if (hBitmap != IntPtr.Zero)
{
SelectObject(memDc, hOldBitmap);
DeleteObject(hBitmap);
}
DeleteDC(memDc);
}
}
However, this obviously redraw the whole window every time it's called. It's quite a performance drain on large window. (even on my top of the line PC, which make me wonder how people could handle that in Win2K)
If I read the Microsoft paper on the layered window, it says: UpdateLayeredWindow always updates the entire window. To update part of a window, use the traditional WM_PAINT and set the blend value using SetLayeredWindowAttributes.
I just can't understand the above. How is WM_PAINT supposed to access the layered window bitmap and redraw only part of it on the window? From what I understood, layered windows simply disable the WM_PAINT message and expect the user to draw the window by himself. There's obviously no way to bind the WM_PAINT to the custom drawing done.
Am I missing something very obvious?

After long profiling, I found out it wasn't really the layered window update that was bottleneck. Refreshing the whole screen, the SelectBitmap method above, on a 1920*1200 was taking about 6-8ms. Sure, not very amazing, but plenty enough to refresh at 30 FPS+.
In my case, the performance drains was coming from some thread asking for refresh almost a hundred time per redraw, making everything sluggish. The solution was to break down the refresh/redraw and separate them. One would update (union) a region and the other, when not drawing, would take that region, draw it and then empty it.

Problem with BitBtl and DWM (Windows Aero)

I'm developing an application that has to take screenshots of a fullscreen game. The problem is that I've tried many methods but any of them are able to take the screenshot when the game is in fullscreen mode, it will just take a screenshot of what is under the game and a black rectangle on the top left corner.
Is there any alternative to achieve this goal that doesn't involve hooking? As I'm using C#, which is kind of a bad language to make this kind of things.
This is my code right now:
Bitmap bmp = null;
SIZE size;
size.cx = Screen.PrimaryScreen.Bounds.Width;
size.cy = Screen.PrimaryScreen.Bounds.Height;
IntPtr Src = PlatformInvokeUSER32.GetDC(IntPtr.Zero);
IntPtr Dest = PlatformInvokeGDI32.CreateCompatibleDC(Src);
IntPtr HBitmap = (IntPtr)null;
IntPtr hOld = IntPtr.Zero;
HBitmap = PlatformInvokeGDI32.CreateCompatibleBitmap(Src, size.cx, size.cy);
hOld = (IntPtr)PlatformInvokeGDI32.SelectObject(Dest, HBitmap);
PlatformInvokeGDI32.BitBlt(Dest, 0, 0, size.cx, size.cy, Src, 0, 0, (PlatformInvokeGDI32.SRCCOPY|PlatformInvokeGDI32.CAPTUREBLT));
bmp = System.Drawing.Image.FromHbitmap(HBitmap);
PlatformInvokeGDI32.DeleteDC(Dest);
PlatformInvokeUSER32.ReleaseDC(IntPtr.Zero.GetDesktopWindow(), Src);
PlatformInvokeGDI32.DeleteObject(HBitmap);
This works properly on XP, but when it comes to Vista / 7, I need to disable Aero for this code to work, either it will just take a screenshot of what it's under the game as I said before.