reagents[1] = ReagentManager.GetReagent(reagentName);

            ingredient3ComboBox.Sensitive = true;

            captureButton.Sensitive = true;

            reaction1 = profile.FindReaction(reagents[0], reagents[1]);

            // TODO: really should handle reagent0==reagent1 better

            if ((reaction1 != null) || (reagents[0] == reagents[1]))

            {

                clearReactionButton.Sensitive = recordEnabled;

                clearReactionButton.Visible = true;

                ingredient3ComboBox.Sensitive = true;

                if ((reagentName = GetSelectedReagentName(3)) != null)

                {

                    clearReactionButton.Sensitive = false;

                    clearReactionButton.Visible = false;

                    recipe.AddReagent(reagentName);

                    reagents[2] = ReagentManager.GetReagent(reagentName);

                    if (!reactionKnown)

                    {

                        Gtk.MessageDialog md = new Gtk.MessageDialog((Gtk.Window)Toplevel, 

                            Gtk.DialogFlags.DestroyWithParent,

                            Gtk.MessageType.Error, Gtk.ButtonsType.Ok, 

                            "To do a three-ingredient reaction test, " +

                            "you must first recored the reaction of " +

                            "the first two ingredients.");

                        md.Run();

                        md.Destroy();

                        captureButton.Sensitive = false;

                    }

                    reaction1 = profile.FindReaction(reagents[0], reagents[2]);

                    reaction2 = profile.FindReaction(reagents[1], reagents[2]);

                    if (reactionKnown && (reaction1 == null) && (reaction2 == null))

                    {

                        Gtk.MessageDialog md = new Gtk.MessageDialog((Gtk.Window)Toplevel, 

                            Gtk.DialogFlags.DestroyWithParent,

                            Gtk.MessageType.Error, Gtk.ButtonsType.Ok, 

                            "To do a three-ingredient reaction test, " +

                            "you must first record the reaction of " +

                            "either the first or second ingredient " +

                            "with the third ingredient.");

                        md.Run();

                        md.Destroy();   

                        captureButton.Sensitive = false;

                    }

                    if ((reaction1 == null) && (reagents[0] != reagents[2]))

                    {

                        reactionKnown = false;  

                    }

                    if ((reaction2 == null) && (reagents[1] != reagents[2]))

                    {

                        reactionKnown = false;  

                    }

                }

            }

            else

            {

                reactionKnown = false;

                ingredient3ComboBox.Sensitive = false;

            }

            expectedColor.Set(recipe.BaseColor);

            unmodifiedSwatch.Color = expectedColor;

            //SetExpectedColor(recipeColor.Red, recipeColor.Green, recipeColor.Blue);

            if (reactionKnown)

            {

                reactedColor.Set(recipe.ReactedColor);

                reactionSwatch.Color = reactedColor;

            }

            else

            {

                reactionSwatch.Clear(); 

            }

        }

        unsafe bool CaptureReactionColor()

        {

            // Take a screenshot.

            int screenWidth, screenHeight;

            bool debugScreenshot = false;

            bool enableDebugMenu = false;

            Gdk.Window rootWindow = Gdk.Global.DefaultRootWindow;

            DesertPaintLab.AppSettings.Get("ScreenWidth", out screenWidth);

            DesertPaintLab.AppSettings.Get("ScreenHeight", out screenHeight);

            DesertPaintLab.AppSettings.Get("EnableDebugMenu", out enableDebugMenu);

            DesertPaintLab.AppSettings.Get("DebugScreenshot", out debugScreenshot);

            Gdk.Image rootImage = rootWindow.GetImage(0, 0, screenWidth, screenHeight);

            screenBuffer.GetFromImage(rootImage, rootImage.Colormap, 0, 0, 0, 0, screenWidth, screenHeight);

            //screenBuffer.GetFromDrawable(rootWindow,

            //  rootWindow.Colormap, 0, 0, 0, 0, screenWidth, screenHeight);

            int stride = screenBuffer.Rowstride;

            byte* pixBytes = (byte*)screenBuffer.Pixels;

            int redPixelStart = -1;

            StreamWriter log = null;

            if (enableDebugMenu)

            {

                string logfile = FileUtils.FindNumberedFile("DesertPaintLab_Capture", "log", Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments));

                log = new StreamWriter(logfile);

                ReactionRecorder.Instance.Log = log;

            }

            isCaptured = ReactionRecorder.Instance.CaptureReaction(pixBytes, screenWidth, screenHeight, stride, ref reactedColor, ref redPixelStart);

            if (log != null)

            {

                log.Flush();

                log.Close();

                log = null;

            }

            if (enableDebugMenu && debugScreenshot)

            {

                if (!isCaptured)

                {

                    // write out the whole screenshot on a failure to capture

                    string screenshotDir = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);

                    string filename = FileUtils.FindNumberedFile("DesertPaintLab_Colormatch", "png", screenshotDir);

                    screenBuffer.Save(filename, "png");

                }

                else

                {

                    // record the swatch that was captured

                    // convert to pixel offset instead of byte

                    int redPixelStartX = (redPixelStart % stride) / 3;

                    int redPixelStartY = (redPixelStart / stride);

                    // write out the screenshot

                    string screenshotDir = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);

                    string filename = FileUtils.FindNumberedFile("DesertPaintLab_Colormatch", "png", screenshotDir);

                    int captureAreaWidth = Math.Min(64, screenWidth - redPixelStartX + 64);

                    int captureAreaHeight = Math.Min(64, screenHeight - redPixelStartY + 64);

                    Gdk.Pixbuf outPixBuf = new Gdk.Pixbuf(screenBuffer, Math.Max(0, redPixelStartX - 32), Math.Max(0, redPixelStartY - 32), captureAreaWidth, captureAreaHeight);

                    //screenBuffer.Save(filename, "png");

                    outPixBuf.Save(filename, "png");

                }

            }

            //screenBuffer.Save("screenshot.png", "png");

            return isCaptured;

        }

        protected virtual void OnCapture(object sender, System.EventArgs e)

        {

            if (CaptureReactionColor())

            {

                string warning = "";

                if (reactedColor.Red == 0)

                {

                    warning = warning + "\nRed is too low.";

                }

                if (reactedColor.Green == 0)

                {

                    warning = warning + "\nGreen is too low.";  

                }

                if (reactedColor.Blue == 0)

                {

                    warning = warning + "\nBlue is too low.";   

                }

                if (reactedColor.Red == 255)

                {

                    warning = warning + "\nRed is too high.";

                }

                if (reactedColor.Green == 255)

                {

                    warning = warning + "\nGreen is too high."; 

                }

                if (reactedColor.Blue == 255)

                {

                    warning = warning + "\nBlue is too high.";  

                }

                if (warning.Length != 0)

                {

                    isCaptured = true;

                    Gtk.MessageDialog md = new Gtk.MessageDialog((Gtk.Window)Toplevel, 

                    Gtk.DialogFlags.DestroyWithParent,

                    Gtk.MessageType.Error, Gtk.ButtonsType.Ok, 

                    "Reaction clipped.  You will need to do a " +

                    "3-way reaction to test this pair.  Details: " +

                    warning);

                    md.Run();

                    md.Destroy();

                }

                else

                {

                    this.reactionSwatch.Color = reactedColor;