apply dark mode to all forms automatically

Based on kbilsted#104
Rdipardo did all the hard work here, this is just a refinement.

This makes it easy for plugin makers to apply dark mode to all forms.
Rather than having to individually select themes
to apply for each control, sensible defaults are applied based on
each control's type.
This PR also allows the color changes to propagate recursively
to a form's child forms, if it has any.

Demo Plugin/NppManagedPluginDemo/Demo.cs

@@ -2,7 +2,9 @@
 using System;
 using System.IO;
 using System.Text;
+using System.Collections.Generic;
 using System.Drawing;
+using System.Reflection;
 using System.Threading;
 using System.Windows.Forms;
 using System.Drawing.Imaging;
@@ -38,7 +40,13 @@ public static void OnNotification(ScNotification notification)
         {
             if (notification.Header.Code == (uint)SciMsg.SCN_CHARADDED)
             {
-                Kbg.Demo.Namespace.Main.doInsertHtmlCloseTag((char)notification.Character);
+                Demo.Namespace.Main.doInsertHtmlCloseTag((char)notification.Character);
+            }
+            // dark mode (de-)activated
+            if (notification.Header.Code == (uint)NppMsg.NPPN_DARKMODECHANGED)
+            {
+                INotepadPPGateway notepad = new NotepadPPGateway();
+                Demo.Namespace.Main.ToggleDarkMode(Demo.Namespace.Main.frmGoToLine, notepad.IsDarkModeEnabled());
             }
         }
 
@@ -57,7 +65,7 @@ class Main
         static string keyName = "doCloseTag";
         static bool doCloseTag = false;
         static string sessionFilePath = @"C:\text.session";
-        static frmGoToLine frmGoToLine = null;
+        static internal frmGoToLine frmGoToLine = null;
         static internal int idFrmGotToLine = -1;
 
         // toolbar icons
@@ -179,6 +187,104 @@ static internal void PluginCleanUp()
         {
             Win32.WritePrivateProfileString(sectionName, keyName, doCloseTag ? "1" : "0", iniFilePath);
         }
+
+        /// <summary>
+        /// Apply dark mode (or re-apply light mode) to the controls of any form.<br></br>
+        /// This method currently supports colorizing the following types of controls:<br></br>
+        /// - Buttons<br></br>
+        /// - Labels<br></br>
+        /// - LinkLabels<br></br>
+        /// - ComboBoxes<br></br>
+        /// - CheckBoxes<br></br>
+        /// - ListBoxes<br></br>
+        /// - TreeViews<br></br>
+        /// Feel free to add more as needed.<br></br>
+        /// TODO: Figure out best way to customize border colors of controls.
+        /// https://stackoverflow.com/questions/1445472/how-to-change-the-form-border-color-c
+        /// may be a lead.
+        /// </summary>
+        /// <param name="form">a Windows Form</param>
+        /// <param name="isDark">is Notepad++ dark mode on?</param>
+        static internal void ToggleDarkMode(Form form, bool isDark)
+        {
+            if (form == null)
+                return;
+            IntPtr themePtr = notepad.GetDarkModeColors();
+            if (isDark && themePtr == IntPtr.Zero)
+                return;
+            var theme = (DarkModeColors)Marshal.PtrToStructure(themePtr, typeof(DarkModeColors));
+            foreach (Form childForm in form.OwnedForms)
+            {
+                // allow possibility that some forms will have other child forms
+                // JsonTools does this in a couple of places
+                ToggleDarkMode(childForm, isDark);
+            }
+            if (isDark)
+            {
+                form.BackColor = NppDarkMode.BGRToColor(theme.Background);
+                form.ForeColor = NppDarkMode.BGRToColor(theme.Text);
+            }
+            else
+            {
+                form.ResetForeColor();
+                form.ResetBackColor();
+            }
+            foreach (Control ctrl in form.Controls)
+            {
+                if (isDark)
+                {
+                    // this doesn't actually make disabled controls have different colors
+                    // windows forms don't make it easy for the user to choose the
+                    // color of a disabled control. See https://stackoverflow.com/questions/136129/windows-forms-how-do-you-change-the-font-color-for-a-disabled-label
+                    var textTheme = ctrl.Enabled ? theme.Text : theme.DisabledText;
+                    if (ctrl is Button btn)
+                    {
+                        btn.BackColor = NppDarkMode.BGRToColor(theme.SofterBackground);
+                        btn.ForeColor = NppDarkMode.BGRToColor(textTheme);
+                    }
+                    else if (ctrl is LinkLabel llbl)
+                    {
+                        llbl.BackColor = NppDarkMode.BGRToColor(theme.ErrorBackground);
+                        llbl.ForeColor = NppDarkMode.BGRToColor(theme.DarkerText);
+                        llbl.LinkColor = NppDarkMode.BGRToColor(theme.LinkText);
+                        llbl.ActiveLinkColor = NppDarkMode.BGRToColor(theme.Text);
+                        llbl.VisitedLinkColor = NppDarkMode.BGRToColor(theme.DarkerText);
+                    }
+                    // other common text-based controls
+                    else if (ctrl is TextBox
+                        || ctrl is Label
+                        || ctrl is ListBox
+                        || ctrl is ComboBox)
+                    {
+                        ctrl.BackColor = NppDarkMode.BGRToColor(theme.PureBackground);
+                        ctrl.ForeColor = NppDarkMode.BGRToColor(textTheme);
+                    }
+                    else if (ctrl is TreeView tv)
+                    {
+                        tv.BackColor = NppDarkMode.BGRToColor(theme.HotBackground);
+                        tv.ForeColor = NppDarkMode.BGRToColor(textTheme);
+                    }
+                    else
+                    {
+                        // other controls I haven't thought of yet
+                        ctrl.BackColor = NppDarkMode.BGRToColor(theme.SofterBackground);
+                        ctrl.ForeColor = NppDarkMode.BGRToColor(textTheme);
+                    }
+                }
+                else // normal light mode
+                {
+                    ctrl.ResetForeColor();
+                    ctrl.ResetBackColor();
+                    if (ctrl is LinkLabel llbl)
+                    {
+                        llbl.LinkColor = Color.Blue;
+                        llbl.ActiveLinkColor = Color.Red;
+                        llbl.VisitedLinkColor = Color.Purple;
+                    }
+                }
+            }
+            Marshal.FreeHGlobal(themePtr);
+        }
         #endregion
 
         #region " Menu functions "
@@ -443,6 +549,7 @@ static void DockableDlgDemo()
                     Win32.SendMessage(PluginBase.nppData._nppHandle, (uint) NppMsg.NPPM_SETMENUITEMCHECK, PluginBase._funcItems.Items[idFrmGotToLine]._cmdID, 0);
                 }
             }
+            ToggleDarkMode(frmGoToLine, notepad.IsDarkModeEnabled());
             frmGoToLine.textBox1.Focus();
         }