3set: delete by letter pieces when assemblying

src/net/torvald/terrarum/gamecontroller/IME.kt

@@ -12,6 +12,7 @@ data class TerrarumInputMethod(
         val name: String,
         // (headkey, shiftin, altgrin)
         val acceptChar: (Int, Boolean, Boolean) -> Pair<String, String>, // Pair<Display Char, Output Char if any>
+        val backspace: () -> String,
         val endCompose: () -> String,
         val reset: () -> Unit,
         val composing: () -> Boolean
@@ -109,6 +110,8 @@ object IME {
         return TerrarumInputMethod(name, { headkey, shifted, alted ->
             val a = jsval.invokeMember("accept", headkey, shifted, alted)
             a.getArrayElement(0).asString() to a.getArrayElement(1).asString()
+        }, {
+            jsval.invokeMember("backspace").asString()
         }, {
             jsval.invokeMember("end").asString()
         }, {

src/net/torvald/terrarum/ui/UIItemTextLineInput.kt

@@ -176,8 +176,7 @@ class UIItemTextLineInput(
                 }
                 else if (keycodes.contains(Input.Keys.BACKSPACE)) {
                     if (ime != null && ime.composing()) {
-                        // TODO ime.backspace() instead of resetIME()
-                        resetIME()
+                        composingView = CodepointSequence(ime.backspace().toCodePoints())
                     }
                     else if (cursorX <= 0) {
                         cursorX = 0
@@ -185,6 +184,7 @@ class UIItemTextLineInput(
                         cursorDrawScroll = 0
                     }
                     else {
+                        endComposing()
                         if (cursorX > 0) {
                             while (true) {
                                 cursorX -= 1