Programming Forums > Application Development > C++

kipale · Nov 8th, 2007, 2:06 PM

Hi, I want to write a program that reads a pixel on the screen and then does A if the pixel is of certain color and B if it's not. So the change of the color of the pixel (x,y) on my screen can trigger things. Can this be done easily? I'm a newbie programmer so I don't really have any idea of where to start. I just really need a program that can do this. Also if you know that it can be done more easily with some other language than C++ then feel free to tell me because I can always learn the language enough to write the effect-part.

Wizard1988 · Nov 8th, 2007, 2:11 PM

This is in C# but you should be able to use the information contained in the article to write a similar program in C++

http://sharpinsights.wordpress.com/2...r-under-mouse/

InfiNate · Nov 8th, 2007, 2:23 PM

I recently did this in C#, I had to use a pinvoke to use some windows methods.

The only difficulty's i ran into was to read the pixels that were 'outside' of my current program. I cant remember exactly how I did it, ( i think there was a default handle to use ).

I will post my code tonight when I have access to it.

Wizard1988 · Nov 8th, 2007, 2:27 PM

Were you using the DC of the application window?? Try getting the DC of the desktop window instead

andro · Nov 8th, 2007, 3:33 PM

java.awt.Robot

InfiNate · Nov 8th, 2007, 4:08 PM

Quote:

Originally Posted by andro

java.awt.Robot

It's really simple to do this in java. All you need to do is call getPixelColor(int,int) and it returns the color.

It's slightly more complicated to do it in c++/c# because of the window handle stuff.

InfiNate · Nov 8th, 2007, 5:47 PM

Here it is in c#, should be easy to convert it to c++.

(Toggle Plain Text)

using System;
using System.Drawing;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;

class ScreenReader
{
        #region Imported Functions
        [DllImport("gdi32.dll")]
        public static extern IntPtr CreateDC(string strDriver, string strDevice,
                                             string strOutput, IntPtr pData);
        [DllImport("gdi32.dll")]
        public static extern bool DeleteDC(IntPtr hdc);

        [DllImport("gdi32.dll")]
        public static extern int GetPixel(IntPtr hdc, int x, int y);
        #endregion

        public static Color getColorAt(int x, int y)
        {
            IntPtr hdcScreen = CreateDC("Display", null, null, IntPtr.Zero);
            Color clr = ColorTranslator.FromWin32(GetPixel(hdcScreen, x, y));
            DeleteDC(hdcScreen);
            return clr;
        }
}

kipale · Nov 9th, 2007, 12:28 AM

Thank you, everyone. Great help

I'm gonna try some of this later today or tomorrow, I'm sure I'll get something done.

Wizard1988 · Nov 9th, 2007, 12:30 AM

Is it a good idea to keep keep on recreating hdcScreen each time you call getColorAt ?

InfiNate · Nov 9th, 2007, 1:50 AM

Quote:

Originally Posted by Wizard1988

Is it a good idea to keep keep on recreating hdcScreen each time you call getColorAt ?

Probably not. In my actual code i used theres another method where I passed in a hdcScreen for that reason. I suppose I could have just made a member variable for the class.

Nov 8th, 2007, 2:06 PM	#1
kipale Newbie Join Date: Nov 2007 Posts: 2 Rep Power: 0	How to do this... Hi, I want to write a program that reads a pixel on the screen and then does A if the pixel is of certain color and B if it's not. So the change of the color of the pixel (x,y) on my screen can trigger things. Can this be done easily? I'm a newbie programmer so I don't really have any idea of where to start. I just really need a program that can do this. Also if you know that it can be done more easily with some other language than C++ then feel free to tell me because I can always learn the language enough to write the effect-part.

Nov 8th, 2007, 2:11 PM	#2
Wizard1988 Professional Programmer Join Date: Oct 2005 Location: Chitown Posts: 417 Rep Power: 3	Re: How to do this... This is in C# but you should be able to use the information contained in the article to write a similar program in C++ http://sharpinsights.wordpress.com/2...r-under-mouse/ __________________ JG-Webdesign

Nov 8th, 2007, 2:23 PM	#3
InfiNate Newbie Join Date: Nov 2007 Location: Waterloo, ON Posts: 20 Rep Power: 0	Re: How to do this... I recently did this in C#, I had to use a pinvoke to use some windows methods. The only difficulty's i ran into was to read the pixels that were 'outside' of my current program. I cant remember exactly how I did it, ( i think there was a default handle to use ). I will post my code tonight when I have access to it.

Nov 8th, 2007, 2:27 PM	#4
Wizard1988 Professional Programmer Join Date: Oct 2005 Location: Chitown Posts: 417 Rep Power: 3	Re: How to do this... Were you using the DC of the application window?? Try getting the DC of the desktop window instead __________________ JG-Webdesign

Nov 8th, 2007, 3:33 PM	#5
andro Professional Programmer Join Date: Oct 2005 Location: California Posts: 294 Rep Power: 3	Re: How to do this... java.awt.Robot __________________ http://www.kevinherron.com/

Nov 8th, 2007, 5:47 PM	#7
InfiNate Newbie Join Date: Nov 2007 Location: Waterloo, ON Posts: 20 Rep Power: 0	Re: How to do this... Here it is in c#, should be easy to convert it to c++. (Toggle Plain Text) using System; using System.Drawing; using System.Collections.Generic; using System.Text; using System.Runtime.InteropServices; class ScreenReader { #region Imported Functions [DllImport("gdi32.dll")] public static extern IntPtr CreateDC(string strDriver, string strDevice, string strOutput, IntPtr pData); [DllImport("gdi32.dll")] public static extern bool DeleteDC(IntPtr hdc); [DllImport("gdi32.dll")] public static extern int GetPixel(IntPtr hdc, int x, int y); #endregion public static Color getColorAt(int x, int y) { IntPtr hdcScreen = CreateDC("Display", null, null, IntPtr.Zero); Color clr = ColorTranslator.FromWin32(GetPixel(hdcScreen, x, y)); DeleteDC(hdcScreen); return clr; } } using System; using System.Drawing; using System.Collections.Generic; using System.Text; using System.Runtime.InteropServices; class ScreenReader { #region Imported Functions [DllImport("gdi32.dll")] public static extern IntPtr CreateDC(string strDriver, string strDevice, string strOutput, IntPtr pData); [DllImport("gdi32.dll")] public static extern bool DeleteDC(IntPtr hdc); [DllImport("gdi32.dll")] public static extern int GetPixel(IntPtr hdc, int x, int y); #endregion public static Color getColorAt(int x, int y) { IntPtr hdcScreen = CreateDC("Display", null, null, IntPtr.Zero); Color clr = ColorTranslator.FromWin32(GetPixel(hdcScreen, x, y)); DeleteDC(hdcScreen); return clr; } }

Nov 9th, 2007, 12:28 AM	#8
kipale Newbie Join Date: Nov 2007 Posts: 2 Rep Power: 0	Re: How to do this... Thank you, everyone. Great help I'm gonna try some of this later today or tomorrow, I'm sure I'll get something done.

Nov 9th, 2007, 12:30 AM	#9
Wizard1988 Professional Programmer Join Date: Oct 2005 Location: Chitown Posts: 417 Rep Power: 3	Re: How to do this... Is it a good idea to keep keep on recreating hdcScreen each time you call getColorAt ? __________________ JG-Webdesign

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Programming Forums > Application Development > C++

How to do this...