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POcreate graphics of entire screen
 

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  1. POcreate graphics of entire screen
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    <p>I ame using a class to increase and decrease the gamma of all my screens, then i start the program and increase or decrease the gamma it works fine, but after a while (20 seconds or so) it does not work anymore, ive located the problem and it seems to be the <code>Graphics.FromHwnd(IntPtr.Zero).GetHdc().ToInt32();</code> i need to refresh this and then it works again. in the example code this is only done once during initialisation, but to make it work i have pasted the line inside the <code>SetBrightness()</code> method, so everytime it is refreshed. is it ok to do it like this or can i expect problems?</p> <p>This is the code:</p> <pre><code>public static class Brightness { [DllImport("gdi32.dll")] private unsafe static extern bool SetDeviceGammaRamp(Int32 hdc, void* ramp); private static bool initialized = false; private static Int32 hdc; private static void InitializeClass() { if (initialized) return; //Get the hardware device context of the screen, we can do //this by getting the graphics object of null (IntPtr.Zero) //then getting the HDC and converting that to an Int32. hdc = Graphics.FromHwnd(IntPtr.Zero).GetHdc().ToInt32(); initialized = true; } public static unsafe bool SetBrightness(short brightness) { InitializeClass(); hdc = Graphics.FromHwnd(IntPtr.Zero).GetHdc().ToInt32(); if (brightness &gt; 255) brightness = 255; if (brightness &lt; 0) brightness = 0; short* gArray = stackalloc short[3 * 256]; short* idx = gArray; for (int j = 0; j &lt; 3; j++) { for (int i = 0; i &lt; 256; i++) { int arrayVal = i * (brightness + 128); if (arrayVal &gt; 65535) arrayVal = 65535; *idx = (short)arrayVal; idx++; } } //For some reason, this always returns false? bool retVal = SetDeviceGammaRamp(hdc, gArray); //Memory allocated through stackalloc is automatically free'd //by the CLR. return retVal; } } </code></pre> <p>This is how it is called:</p> <pre><code>short gammaValue = 128; void gammaUp_OnButtonDown(object sender, EventArgs e) { if (gammaValue &lt; 255) { gammaValue += 10; if (gammaValue &gt; 255) gammaValue = 255; Brightness.SetBrightness(gammaValue); } } void gammaDown_OnButtonDown(object sender, EventArgs e) { if (gammaValue &gt; 0) { gammaValue -= 10; if (gammaValue &lt; 0) gammaValue = 0; Brightness.SetBrightness(gammaValue); } } </code></pre>
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    1. USJeffnl
    1. USJeffnl
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    1. CODo you have an example of how SetBrightness is called? i.e. how often, what else is changing hdc in the mean time...
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      1. POcreate graphics of entire screen
      1. USJim Jeffries
    2. CO@jamesj nothing else is changing hdc in the program except this code
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      1. POcreate graphics of entire screen
      1. USJeffnl
 

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