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[Help] Last time with GetPixel

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kitterz
Grandmaster Cheater Supreme

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Joined: 24 Dec 2007
Posts: 1268

Posted: Fri Jul 11, 2008 11:09 am Post subject: [Help] Last time with GetPixel

Haha I know I am posting a lot....but his will be the last one for awhile.

I have this code

Code:

#include "stdafx.h"
#include <windows.h>
#include <iostream>

HINSTANCE hInstApp = NULL;

COLORREF CColor;
HDC SColor;
POINT Pos;

int redv;
int bluev;
int greenv;

DWORD GPA = (DWORD)GetProcAddress(LoadLibrary("GDI32.DLL"), "GetPixel")+ 5;
_declspec(naked) COLORREF GetPix(HDC hdc, int nXPos, int nYPos) {
_asm
{
mov edi, edi
push ebp
mov ebp, esp
jmp[GPA]
}
}

/////////////////////////////////
int main() {

while (1==1) {
      SColor = GetDC(HWND_DESKTOP);
      GetCursorPos (&Pos);
      CColor = GetPix (SColor,Pos.x,Pos.y);

      redv = GetRValue(CColor);
      greenv = GetGValue(CColor);
      bluev = GetBValue(CColor);

      cout << "Red: " << redv << endl;
      cout << "Green: " << greenv << endl;
      cout << "Blue: " << bluev << endl;
      cout << endl;

      //Sleep (1000);
}

return 0;
}

But after showing like 10 color points, it gives the error

Quote:

Unhandled exception at 0x00401060 in Test.exe: 0xC0000005: Access violation writing location 0x00130000.

Any Solutions?

Flyte
Peanuts!!!!

Reputation: 6

Joined: 19 Apr 2006
Posts: 1887
Location: Canada

Posted: Fri Jul 11, 2008 1:31 pm Post subject:

Open it in a debugger and figure out where the exception is being generated, then I might be able to help you. Also, mov edi, edi is not needed in your trampoline. The only reason that instruction is there is to provide a buffer for hot patching.

Symbol
I'm a spammer

Reputation: 0

Joined: 18 Apr 2007
Posts: 5094
Location: Israel.

Posted: Fri Jul 11, 2008 1:36 pm Post subject:

Flyte wrote:

Open it in a debugger and figure out where the exception is being generated, then I might be able to help you.

Also, mov edi, edi is not needed in your trampoline. The only reason that instruction is there is to provide a buffer for hot patching.

Why doesn't it use NOPs then?

Flyte
Peanuts!!!!

Reputation: 6

Joined: 19 Apr 2006
Posts: 1887
Location: Canada

Posted: Fri Jul 11, 2008 1:48 pm Post subject:

Symbol wrote:

Why doesn't it use NOPs then?

NOPs are used to pad the spaces between functions (INT3 is used in a debug build), so if they did use NOP it would look ugly (and be potentially confusing) in a debugger.

Fun fact: NOP is just an alias mnemonic for xchg eax, eax.

kitterz
Grandmaster Cheater Supreme

Reputation: 0

Joined: 24 Dec 2007
Posts: 1268

Posted: Fri Jul 11, 2008 2:02 pm Post subject:

Flyte wrote:

Well im not sure how to load it into a debugger since its like a dos program....but I do know that it is screws up when calling

Code:

COLORREF GetPix(HDC hdc, int nXPos, int nYPos)

Flyte
Peanuts!!!!

Reputation: 6

Joined: 19 Apr 2006
Posts: 1887
Location: Canada

Posted: Fri Jul 11, 2008 2:38 pm Post subject:

The following code works perfectly for me.

Code:

#include <windows.h>
#include <iostream>

DWORD GetPixelProc = (DWORD)GetProcAddress( LoadLibrary( "GDI32.DLL" ), "GetPixel" ) + 5;

COLORREF __declspec( naked ) GetPix( HDC hdc, int nXPos, int nYPos )
{
__asm {
mov edi, edi
push ebp
mov ebp, esp
jmp [GetPixelProc]
}
}

void main( void )
{
COLORREF crColor;
POINT pPoint;
//-------

for(;; Sleep( 500 )) {
GetCursorPos( &pPoint );
crColor = GetPix( GetDC( HWND_DESKTOP ), pPoint.x, pPoint.y );
std::cout << "Red:\t" << (int)GetRValue( crColor ) << std::endl;
std::cout << "Green:\t" << (int)GetGValue( crColor ) << std::endl;
std::cout << "Blue:\t" << (int)GetBValue( crColor ) << std::endl << std::endl;
}
}

Edit: Crashes when you remove Sleep(500), I assume that it is because the console is being flooded with output, and has nothing to do with the trampolined API.

kitterz
Grandmaster Cheater Supreme

Reputation: 0

Joined: 24 Dec 2007
Posts: 1268

Posted: Fri Jul 11, 2008 3:32 pm Post subject:

Flyte wrote:

The following code works perfectly for me.

Code:

Edit: Crashes when you remove Sleep(500), I assume that it is because the console is being flooded with output, and has nothing to do with the trampolined API.

This works for you? Interesting. Cause it still gives me the Unhandled exception error.

kitterz
Grandmaster Cheater Supreme

Reputation: 0

Joined: 24 Dec 2007
Posts: 1268

Posted: Fri Jul 11, 2008 9:06 pm Post subject:

x0r wrote:

Probably because you're on Windows XP SP1 or earlier.

Nah im SP2

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