TempUtils.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace Menora
{
    class TempUtils
    {
        [DllImport("user32.dll")]
        public static extern IntPtr GetDC(IntPtr hWnd);
        [DllImport("user32.dll")]
        public static extern void ReleaseDC(IntPtr hDC, IntPtr hWnd);
        [DllImport("gdi32.dll")]
        public static extern int GetDeviceGammaRamp(IntPtr hDC, ref RAMP lpRamp);
        [DllImport("gdi32.dll")]
        public static extern bool SetDeviceGammaRamp(IntPtr hDC, ref RAMP lpRamp);

        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
        public struct RAMP
        {
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 256)]
            public UInt16[] Red;
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 256)]
            public UInt16[] Green;
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 256)]
            public UInt16[] Blue;
        }
        private static int lastAppliedTemperature = 6500;

        // Thanks to http://www.tannerhelland.com/4435/convert-temperature-rgb-algorithm-code/
        private static void ComputeRamp(int tmpKelvin, out int rMultiplier, out int gMultiplier, out int bMultiplier)
        {
            double tmpCalc;
            tmpKelvin = Math.Min(40000, Math.Max(1000, tmpKelvin + 100));
            tmpKelvin = (int)Math.Round(tmpKelvin / 100.0d, 0);
            
            // Red
            if (tmpKelvin < 66)
            {
                rMultiplier = 255;
            }
            else
            {
                tmpCalc = tmpKelvin - 60;
                tmpCalc = 329.698727446 * Math.Pow(tmpCalc, -0.1332047592);
                rMultiplier = (int) Math.Max(0, Math.Min(255, tmpCalc));
            }

            // Green
            if (tmpKelvin <= 66)
            {
                tmpCalc = tmpKelvin;
                tmpCalc = 99.4708025861 * Math.Log(tmpCalc) - 161.1195681661;
                gMultiplier = (int)Math.Max(0, Math.Min(255, tmpCalc));
            }
            else
            {
                tmpCalc = tmpKelvin - 60;
                tmpCalc = 288.1221695283 * Math.Pow(tmpCalc, -0.0755148492);
                gMultiplier = (int)Math.Max(0, Math.Min(255, tmpCalc));
            }

            // Blue
            if (tmpKelvin >= 66)
            {
                bMultiplier = 255;
            }
            else if (tmpKelvin <= 19)
            {
                bMultiplier = 0;
            }
            else
            {
                tmpCalc = tmpKelvin - 10;
                tmpCalc = 138.5177312231 * Math.Log(tmpCalc) - 305.0447927307;
                bMultiplier = (int)Math.Max(0, Math.Min(255, tmpCalc));
            }
        }

        private static void ApplyGammaUnchecked(int tmpKelvin)
        {
            IntPtr hdc = GetDC(IntPtr.Zero);
            RAMP ramp = new RAMP();
            int rMultiplier, gMultiplier, bMultiplier;
            ComputeRamp(tmpKelvin, out rMultiplier, out gMultiplier, out bMultiplier);
            // Fill the RGB values
            ramp.Red = new ushort[256];
            ramp.Green = new ushort[256];
            ramp.Blue = new ushort[256];
            for (int i = 0; i < 256; i++)
            {
                ramp.Red[i] = (ushort)(i * 256 * rMultiplier / 255);
                ramp.Green[i] = (ushort)(i * 256 * gMultiplier / 255);
                ramp.Blue[i] = (ushort)(i * 256 * bMultiplier / 255);
            }
            SetDeviceGammaRamp(hdc, ref ramp);
            ReleaseDC(hdc, IntPtr.Zero);
            lastAppliedTemperature = tmpKelvin;
        }

        public static void ApplyGamma(int tmpKelvin)
        {
            while (Math.Abs(tmpKelvin - lastAppliedTemperature) >= 500)
            {
                if (tmpKelvin > lastAppliedTemperature)
                    ApplyGammaUnchecked(Math.Min(tmpKelvin, lastAppliedTemperature + 500));
                else if (tmpKelvin < lastAppliedTemperature)
                    ApplyGammaUnchecked(Math.Max(tmpKelvin, lastAppliedTemperature - 500));
            }
            ApplyGammaUnchecked(tmpKelvin);
        }
    }
}