Moving text cursor using mice

src/main/kotlin/ru/dbotthepony/mc/otm/client/screen/panels/TextInputPanel.kt

@@ -6,11 +6,15 @@ import com.mojang.blaze3d.systems.RenderSystem
 import com.mojang.blaze3d.vertex.DefaultVertexFormat
 import com.mojang.blaze3d.vertex.PoseStack
 import com.mojang.blaze3d.vertex.VertexFormat
+import it.unimi.dsi.fastutil.chars.Char2IntAVLTreeMap
+import it.unimi.dsi.fastutil.chars.Char2IntFunction
+import it.unimi.dsi.fastutil.chars.Char2IntOpenHashMap
 import it.unimi.dsi.fastutil.chars.CharOpenHashSet
 import it.unimi.dsi.fastutil.ints.Int2ObjectAVLTreeMap
 import it.unimi.dsi.fastutil.ints.Int2ObjectMap
 import net.minecraft.client.gui.screens.Screen
 import net.minecraft.client.renderer.GameRenderer
+import org.joml.Vector2i
 import ru.dbotthepony.mc.otm.client.isCtrlDown
 import ru.dbotthepony.mc.otm.client.isKeyDown
 import ru.dbotthepony.mc.otm.client.isShiftDown
@@ -929,9 +933,69 @@ open class TextInputPanel<out S : Screen>(
 	override fun mouseClickedInner(x: Double, y: Double, button: Int): Boolean {
 		selections.clear()
 		requestFocus()
+
+		val (lx, ly) = screenToLocal(x, y)
+		val pos = localToText(lx, ly)
+		cursorLine = pos.y
+		cursorCharacter = pos.x
+
 		return true
 	}
 
+	fun localToText(x: Float, y: Float): Vector2i {
+		if (lines.isEmpty())
+			return Vector2i(0, 0)
+
+		val line = (y / (font.lineHeight + 2f)).toInt().coerceIn(0, lines.size - 1)
+		val sLine = this[line] ?: return Vector2i(0, line)
+
+		if (x <= 0f)
+			return Vector2i(0, line)
+		else if (x >= font.width(sLine))
+			return Vector2i(sLine.length, line)
+
+		// binary search attempt
+		// simply: sucks
+		/*@Suppress("name_shadowing")
+		var x = x
+		var start = 0
+		var end = sLine.length - 1
+
+		while (start < end - 1) {
+			val split = (end - start) / 2
+			val before = font.width(sLine.substring(start, start + split))
+
+			if (x < before) {
+				end = start + split
+			} else if (x > before) {
+				x -= before
+				start += split
+			} else {
+				break
+			}
+		}
+
+		return Vector2i(start, line)*/
+
+		val cache = Char2IntOpenHashMap()
+		var accumulatedWidth = 0f
+
+		for ((i, char) in sLine.withIndex()) {
+			val width = cache.computeIfAbsent(char, Char2IntFunction { font.width(it.toString()) })
+
+			if (x in accumulatedWidth .. accumulatedWidth + width) {
+				if (x - accumulatedWidth < width / 2)
+					return Vector2i(i, line)
+				else
+					return Vector2i(i + 1, line)
+			} else {
+				accumulatedWidth += width
+			}
+		}
+
+		return Vector2i(sLine.length, line)
+	}
+
 	private enum class CharType {
 		SPACES {
 			override fun contains(input: Char): Boolean {