From 984e30cc4c037f7c0a9997384b5c4aa994d62ee0 Mon Sep 17 00:00:00 2001
From: cosmonaut <evan@moonside.games>
Date: Thu, 25 Mar 2021 15:57:26 -0700
Subject: [PATCH] add system for text input

---
 src/Game.cs           | 40 ++++++++++++++++++++++++++++++++++++++++
 src/Input/Input.cs    | 11 +++++++++++
 src/Input/Keyboard.cs | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 86 insertions(+)

diff --git a/src/Game.cs b/src/Game.cs
index 8c528eaf..fa9d3be9 100644
--- a/src/Game.cs
+++ b/src/Game.cs
@@ -4,6 +4,7 @@ using MoonWorks.Audio;
 using MoonWorks.Graphics;
 using MoonWorks.Input;
 using MoonWorks.Window;
+using System.Text;
 
 namespace MoonWorks
 {
@@ -107,6 +108,10 @@ namespace MoonWorks
                     case SDL.SDL_EventType.SDL_QUIT:
                         quit = true;
                         break;
+
+                    case SDL.SDL_EventType.SDL_TEXTINPUT:
+                        HandleTextInput(_event);
+                        break;
                 }
             }
         }
@@ -114,5 +119,40 @@ namespace MoonWorks
         protected abstract void Update(double dt);
 
         protected abstract void Draw(double dt, double alpha);
+
+        private void HandleTextInput(SDL2.SDL.SDL_Event evt)
+        {
+            // Based on the SDL2# LPUtf8StrMarshaler
+            unsafe
+            {
+                int bytes = MeasureStringLength(evt.text.text);
+                if (bytes > 0)
+                {
+                    /* UTF8 will never encode more characters
+                        * than bytes in a string, so bytes is a
+                        * suitable upper estimate of size needed
+                        */
+                    char* charsBuffer = stackalloc char[bytes];
+                    int chars = Encoding.UTF8.GetChars(
+                        evt.text.text,
+                        bytes,
+                        charsBuffer,
+                        bytes
+                    );
+
+                    for (int i = 0; i < chars; i += 1)
+                    {
+                        Inputs.OnTextInput(charsBuffer[i]);
+                    }
+                }
+            }
+        }
+
+		private unsafe static int MeasureStringLength(byte* ptr)
+		{
+			int bytes;
+			for (bytes = 0; *ptr != 0; ptr += 1, bytes += 1);
+			return bytes;
+		}
     }
 }
diff --git a/src/Input/Input.cs b/src/Input/Input.cs
index 5111acff..43baf60b 100644
--- a/src/Input/Input.cs
+++ b/src/Input/Input.cs
@@ -1,4 +1,5 @@
 using SDL2;
+using System;
 using System.Collections.Generic;
 
 namespace MoonWorks.Input
@@ -10,6 +11,8 @@ namespace MoonWorks.Input
 
         List<Gamepad> gamepads = new List<Gamepad>();
 
+        public static event Action<char> TextInput;
+
         internal Inputs()
         {
             Keyboard = new Keyboard();
@@ -45,5 +48,13 @@ namespace MoonWorks.Input
         {
             return gamepads[slot];
         }
+
+        internal static void OnTextInput(char c)
+        {
+            if (TextInput != null)
+            {
+                TextInput(c);
+            }
+        }
     }
 }
diff --git a/src/Input/Keyboard.cs b/src/Input/Keyboard.cs
index efe928bc..3fcc45d2 100644
--- a/src/Input/Keyboard.cs
+++ b/src/Input/Keyboard.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Runtime.InteropServices;
 using SDL2;
 
@@ -9,6 +10,28 @@ namespace MoonWorks.Input
         private ButtonState[] Keys { get; }
         private int numKeys;
 
+		private static readonly char[] TextInputCharacters = new char[]
+		{
+			(char) 2,	// Home
+			(char) 3,	// End
+			(char) 8,	// Backspace
+			(char) 9,	// Tab
+			(char) 13,	// Enter
+			(char) 127,	// Delete
+			(char) 22	// Ctrl+V (Paste)
+		};
+
+        private static readonly Dictionary<Keycode, int> TextInputBindings = new Dictionary<Keycode, int>()
+		{
+			{ Keycode.Home, 	    0 },
+			{ Keycode.End,	        1 },
+            { Keycode.Backspace,    2 },
+			{ Keycode.Tab,	        3 },
+            { Keycode.Return,	    4 },
+            { Keycode.Delete,	    5 }
+			// Ctrl+V is special!
+		};
+
         internal Keyboard()
         {
             SDL.SDL_GetKeyboardState(out numKeys);
@@ -28,6 +51,18 @@ namespace MoonWorks.Input
             {
                 var keyDown = Marshal.ReadByte(keyboardState, keycode);
                 Keys[keycode].Update(Conversions.ByteToBool(keyDown));
+
+                if (Conversions.ByteToBool(keyDown))
+                {
+                    if (TextInputBindings.TryGetValue((Keycode)keycode, out var textIndex))
+                    {
+                        Inputs.OnTextInput(TextInputCharacters[(textIndex)]);
+                    }
+                    else if (IsDown(Keycode.LeftControl) && (Keycode)keycode == Keycode.V)
+                    {
+                        Inputs.OnTextInput(TextInputCharacters[6]);
+                    }
+                }
             }
         }