Need an expert advice regarding GDI & C#

Question

1.00/5 (3 votes)

See more:

Ok, here is the example.
Why XORCycleA doesn't work while XORCycleB works...
Here is quite serious riddle for an expert.
Hope you can "speak" C# and will understand my strings without additional comments :))
XOR_Paint will be invoked each time you move the dialog window and smth overlays it.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
using System.Drawing;
using System.Windows.Forms;
using System.Drawing.Imaging;
namespace ConsoleTestApplication
{
 class Program
 {
 static void Main(string[] args)
 {
  new XOR().ShowDialog();
 }
 }
 internal class XOR : Form
 {
 [DllImport("gdi32.dll")]
 public static extern bool BitBlt(IntPtr hdcDest, int nXDest, int nYDest, int nWidth, int nHeight, IntPtr hdcSrc,
            int nXSrc, int nYSrc, Int32 dwRop);
 [DllImport("gdi32.dll")]
 public static extern bool TextOut(IntPtr hdc, int x, int y, string lpString, int cbString);
 const Int32 SRCCOPY = 0x00CC0020;
 const Int32 SRCAND = 0x008800C6;
 const Int32 SRCINVERT = 0x00660046; // INVERT means XOR
 public XOR()
 {
  // Bit map created once with screen data in it
  bmA = new Bitmap(s.Width, s.Height, PixelFormat.Format32bppRgb);
  Graphics gfxBMP = Graphics.FromImage(bmA);
  gfxBMP.CopyFromScreen(0, 0, 0, 0, new Size(s.Width, s.Height), CopyPixelOperation.SourceCopy);
  gfxBMP.Dispose();
  this.Paint += new PaintEventHandler(XOR_Paint);
 }
 void XOR_Paint(object sender, PaintEventArgs e)
 {
  xorCycleA();
  xorCycleB();
 }
 Bitmap bmA;
 Size s = Screen.PrimaryScreen.Bounds.Size;
 unsafe void xorCycleA()
 {
  Graphics grfxScreen = Graphics.FromHwnd(IntPtr.Zero);
  Graphics grfxBitmap = Graphics.FromImage(bmA);
  bmA.Save(@"c:\before_xorA.bmp", ImageFormat.Bmp);
  IntPtr hdcBitmap = grfxBitmap.GetHdc();
  IntPtr hdcScreen = grfxScreen.GetHdc();
  // without any changes just copy screen data with XOR
  BitBlt(hdcBitmap, 0, 0, bmA.Width, bmA.Height, hdcScreen, 0, 0, SRCINVERT);
  grfxScreen.ReleaseHdc(hdcScreen);
  grfxBitmap.ReleaseHdc(hdcBitmap);
  grfxScreen.Dispose();
  grfxBitmap.Dispose();
  bmA.Save(@"c:\after_xorA.bmp", ImageFormat.Bmp);
 }
 Bitmap bmB;
 unsafe void xorCycleB()
 {
  Graphics grfxScreen = Graphics.FromHwnd(IntPtr.Zero);
  bmB = new Bitmap((int)grfxScreen.VisibleClipBounds.Width,
    (int)grfxScreen.VisibleClipBounds.Height, grfxScreen);
  Graphics grfxBitmap = Graphics.FromImage(bmB);
  bmB.Save(@"c:\before_xorB.bmp", ImageFormat.Bmp);
  IntPtr hdcBitmap = grfxBitmap.GetHdc();
  IntPtr hdcScreen = grfxScreen.GetHdc();
  BitBlt(hdcBitmap, 0, 0, bmB.Width, bmB.Height, hdcScreen, 0, 0, SRCCOPY);
  TextOut(hdcBitmap, 100, 100, "Hi, I'm here", 12);
  // comment BitBlt to make sure the bitmap contains screen data and the string on it inside after_xorB.bmp
  BitBlt(hdcBitmap, 0, 0, bmB.Width, bmB.Height, hdcScreen, 0, 0, SRCINVERT);
  grfxScreen.ReleaseHdc(hdcScreen);
  grfxBitmap.ReleaseHdc(hdcBitmap);
  grfxScreen.Dispose();
  grfxBitmap.Dispose();
  bmB.Save(@"c:\after_xorB.bmp", ImageFormat.Bmp);
 }
 }
}

Posted 9-Jul-11 3:02am

RobbKirk

Add a Solution

Comments

Richard MacCutchan 9-Jul-11 9:16am

The expression "doesn't work" is really no help to anyone. You need to explain in detail what you are trying to do, what results you see and what results you expect. Remember, we cannot see your screen so have no idea what the output may look like.

RobbKirk 9-Jul-11 11:44am

Richard, I don't want to explain to everyone. I need only assistance of GDI expert. Trust me, for those who know BitBlt there is no problem to understand what is this code about.

thatraja 9-Jul-11 12:43pm

Actually, he was asked about the details of the code. Because we have no idea about your code & also don't know what do you want because no clue(Here you just pasted the code with out any clue) so he replied you for further details. Also read again the last line of his comment "Remember, we cannot see your screen so have no idea what the output may look like."

Sergey Alexandrovich Kryukov 9-Jul-11 14:17pm

I agree with Richard. You make your question answerable in principle, but practically not. I could build a project based on your code and try it. But before I do, I always hope to catch a problem from a first glance. In 95% it works. I hope to see exception dump and indication of exceptions marked in the comments of source code. It makes immediate resolution very likely.

Only if I cannot see the problem I would consider building a project and testing. It covers almost all situation; and I offer the resolution. I already helped tens or hundreds of members this way.

However, as I consider my time very valuable, I look at one more thing: does OP ***deserve*** this? An inquirer who is reluctant to provide information I mentioned above (or other helpful information when there are no exceptions) does not pass this simple test. What would make me interested enough to answer to such person?

However, anyone deserves a second chance. You can use "Improve question".
--SA

RobbKirk 9-Jul-11 16:57pm

You have two options: Yes/No
or just skip my question... no one is obliged to dig out of my stupid, idiotic and moron-made crap code...

Sergey Alexandrovich Kryukov 9-Jul-11 23:58pm

You code is pretty well presented and neat.

Nevertheless, it makes little sense. First of all, why using Paint event if you don't even use the instance of Graphics passed via event arguments? You don't paint anything anyway. What is going on is quite clear. All your problems are just about order or events, timing and using or not using certain API. I'm pretty much sure you have enough knowledge to solve the problem.

I don't know how to help you simply because you are stubborn enough to avoid explaining what should be in the bitmap as a result. To me, you both variants are wrong.

If I knew what do you want to do with the screen copy, I would have done it in few minutes. And I'm not sure I would need P/Invoke you use at all; in many cases Graphics.CopyFromScreen(Int32, Int32, Int32, Int32, Size, CopyPixelOperation) would do the trick (did you consider that?).

Please excuse me but... why would you try to present yourself as such a rude person, arrogant, too? Do you think it looks cool?
--SA

RobbKirk 10-Jul-11 0:22am

regarding WM_PAINT and CopyFrom.. I spent 3-4 days changing everything upside down... without success. the code you see here is copy/pasted from "battle-ring" project, trust me I do have reflector and I know what is CopyFromScreen.. please, skip ya concerns regarding these two things.
as I wrote XOR of pre-saved bitmap and screen duznt work. (xorCycleA), while in xorCycleB it works with currently grabbed bitmap arrays.
I'm not rude, I just don't want to spend time for unnecessary comments, as a GDI .NET expert (in my case) would see exactly what this code about without my comments.
And those fat remarks about my rudeness and such are missing target arrows.

Sergey Alexandrovich Kryukov 10-Jul-11 0:28am

You do everything to resist getting solution, which is trivial. I don't think your target arrows are too important to anyone but you. It becomes boring.

Good luck.
--SA

RobbKirk 10-Jul-11 0:31am

sorry that I'm not kissed ya ass.

Philippe Mori 9-Jul-11 13:32pm

If you do not give more details, we cannot help you as we don't what the problem. At least indicate what each cycle is supposed to do and what actually happen.

There might be a problem of incompatible image format as the Bitmap is not constructed the same way and DC might be incompatible.

RobbKirk 9-Jul-11 13:36pm

You'd see in xorCycleB() there's "new Bitmap()" code.
As we could see the bitmap is created from screen DC, and stored in global class data, so next call it's not ==null and I expect it IS compatible - I tried many different approaches, then came to decision to split it into two calls (CycleA and CycleB), and see what's the difference.
Then completely stuck with that...that is why I'm here looking for expert in GDI and .NET combination.

Philippe Mori 9-Jul-11 15:06pm

See my solution for my results. Well I have noticed afterward that some initialization were done in the constructor for the first bitmap.

I think the problem is that the bitmap object is not properly copied into the bitmap device context. Anyway, as mentionned in my solution I was able to get the same result by initializing it (from the screen as I haven't try to do it from the saved image).

RobbKirk 9-Jul-11 15:49pm

I know it works from the screen.. I know.
You said "bitmap object is not properly copied into the bitmap device context" - that's the reason I need someone tells me why, and what should be done to make it correct.
As you can see the xorCycleB takes screenshot, places any Text on it and then XORing with the same screen, and the result is black screen and the text, means the static image data is XORed away.
Same with the Bitmat doesn't work.
It works Ok in my C++ program, and I just need to inject that code inside C# client app.

RobbKirk 9-Jul-11 13:33pm

I disagree, for those, who know what is GDI's BitBlt, there is no problem to understand my desire.
It's very easy and readable code.

Sergey Alexandrovich Kryukov 9-Jul-11 14:20pm

I already explain. You problem looks trivial. However, you should explain what "does not work" means, period.

Thank you.
--SA

RobbKirk 9-Jul-11 15:14pm

"It looks trivial"? Man, I have the same code working in C++ program.
You think I don't know what is BitBlt?
The question is - why BitBlt with XOR doesn't work in XorCycleA if the screen is not changing and bmA contains the screen data.
Means XOR should return black image.
And it's returning black in xorCycleB.

Philippe Mori 9-Jul-11 16:14pm

My guess is that the destination is not initialized from the image. Try using DSTINVERT instead to see if you get the image inverted, or a full black or a full white image.

RobbKirk 10-Jul-11 20:34pm

invertion works, AND, OR as well.

the XOR duznt. and it is BUG, just know that... at least .net 3.5 duznt do it well with pre-saved DC or Bitmap.
I've solved it with unmanaged c++ code...

Dave Kreskowiak 9-Jul-11 14:36pm

The problem here Rob is that we have no idea what YOU expect this code to do. We can understand BlitBlt easily, but since you have code the doesn't work AS EXPECTED, it's YOUR expections that are missing from the question.

DO NOT GIVE ME THE SAME OLD "If you knoew, you'd understand" GARBAGE YOU'VE BEEN GIVING EVERYONE ELSE. The problem is not with the code, but with YOUR understanding on what this stuff does and how it fits together. If it was a problem with just the code, you wouldn't be asking a question. We fix YOU, not the code.

RobbKirk 10-Jul-11 20:30pm

CRAP is exactly what you wrote here. you spent a lot of time for it,
Congratulations.

Dave Kreskowiak 10-Jul-11 23:55pm

Have a nice life.

RobbKirk 11-Jul-11 3:24am

krakovyak, to you too.

Philippe Mori 9-Jul-11 15:24pm

Be aware that under Vista and Windows 7, the system typically keep a copy of the windows so moving the windows after it has been overlapped won't cause a redraw. You have to either move the Windows partly out of the screen or resize it for a paint to occurs.

Also, drawing on screen is essentially independant from the painting of the windows as the Desktop Windows Manager is not an intermediate between the drawing done in memory by WM_PAINT and the actual update of the screen.
Because of this, the result of your code is less predictable than it was on XP (or when desktop composition is disabled on latter OS).

Espen Harlinn 11-Jul-11 13:01pm

OP probably set a new record for CP - All time most offensive poster

RobbKirk 12-Jul-11 12:20pm

I don't care. me about 15+ in IT and never met such blah-blah forum like this one.
I do believe that guys are helpfull, but they talk too much, instead of giving a helping hand.
Finally, I found the solution, and it is NOT trivial... and I really needed GDI expert, as I am not the one.
To cut the crap, if someone need the solution, just poke me up to skype: robbkirk

2 solutions

Add a Solution

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Philippe Mori · Answer 1 · 2011-07-09T08:59:00

The line

BitBlt(hdcBitmap, 0, 0, bmA.Width, bmA.Height, hdcScreen, 0, 0, SRCCOPY);

seem to be missing in version XORCycleA.

What I would think if that even though the bitmap bmA contains the image, hdcBitmap is black without initializing its content from the screen.

Well probably 10 years have elasped since last time I have used BitBlt. At that time,to help debugging, my code was made in a way that I could write directly to the screen instead of in-memory. That way, when I have some problem, I run the debugger so that it don't hide the part where I was drawing and the step through the code.

Create another file in that method and copy the content of hdcBitmap to a file to see if it does what you think.

By the way, the final result is dependent on the order of calling XORCycleA and XORCycleB and the result might differ depending on the system (XP, Vista or Windows 7). In fact, it seems to be related to animation thus the only way to have consistent result is to put a breakpoint (and then rezise the form to force a paint) and ignore the first time the code is called since the first generated result would have the form fading in...

Thus is was not so simple as copying the code... As it was a console application, we had to add reference to make it work (then allows unsafe code) and then understand the subtilities...

Once the SRCCOPY and TextOut lines are added to XORCycleA, both function give essentially the same "after" image (except initially because of the fading of the form in progress that affect the first generated image).

Philippe Mori · Answer 2 · 2011-07-09T10:32:00

Solution 2

If it does not works and you cannot find why (I guees you need cycle A to see difference from last save and cycle B from to output annotated changes), you might try to somehow manually copy the bitmap into the device context...

Do you need to also call SelectObject()?

If that still does not works then you coucl use P/Invoke or a C++/CLI to do it with something that works. Since you already have unsafe code, then it should not matters much to add a C++/CLI that would uses working C++ code.

Posted 9-Jul-11 10:32am

Philippe Mori

Comments

RobbKirk 9-Jul-11 16:53pm

SelectObject needs to be used when want to draw smth.
When Blitting context from one to another no need to Select... because it's just bitmap context.. like a paper for writing, and it is the already saved Bitmap.
Select is used when you use Graphics - methods to draw, that will be applied to "paper" (context).
But in my case XORing duznt work when bitmap is taken from previous capturing.

Need an expert advice regarding GDI & C#

2 solutions

Solution 1

Solution 2

Add your solution here

Preview 0

Need an expert advice regarding GDI & C#

2 solutions

Solution 1

Solution 2

Add your solution here

Preview 0

Existing Members

...or Join us