avm2: Roughly implement `TextField.*IndexAtPoint`

Both implementations currently use `screen_position_to_index`, which
is inaccurate, and that's why these methods still produce a stub warning.
However, this implementation makes some games work, is a lot better than
a perfect implementation which would require a lot of work and time,
and infinitely better than no implementation at all.

core/src/avm2/globals/flash/text/TextField.as

@@ -139,10 +139,7 @@ package flash.text {
             stub_method("flash.text.TextField", "insertXMLText");
         }
 
-        public function getCharIndexAtPoint(x:Number, y:Number):int {
-            stub_method("flash.text.TextField", "getCharIndexAtPoint");
-            return 0;
-        }
+        public native function getCharIndexAtPoint(x:Number, y:Number):int;
 
         public native function getLineLength(lineIndex:int):int;
 
@@ -165,10 +162,7 @@ package flash.text {
             return null;
         }
 
-        public function getLineIndexAtPoint(x:Number, y:Number):int {
-            stub_method("flash.text.TextField", "getLineIndexAtPoint");
-            return 0;
-        }
+        public native function getLineIndexAtPoint(x:Number, y:Number):int;
 
         public native function getLineIndexOfChar(charIndex:int):int;
 

core/src/avm2/globals/flash/text/text_field.rs

@@ -10,8 +10,8 @@ use crate::avm2::Error;
 use crate::display_object::{AutoSizeMode, EditText, TDisplayObject, TextSelection};
 use crate::html::TextFormat;
 use crate::string::AvmString;
-use crate::{avm2_stub_getter, avm2_stub_setter};
-use swf::Color;
+use crate::{avm2_stub_getter, avm2_stub_method, avm2_stub_setter};
+use swf::{Color, Point};
 
 pub fn text_field_allocator<'gc>(
     class: ClassObject<'gc>,
@@ -1469,3 +1469,74 @@ pub fn get_line_index_of_char<'gc>(
         Ok(Value::Number(-1f64))
     }
 }
+
+pub fn get_char_index_at_point<'gc>(
+    activation: &mut Activation<'_, 'gc>,
+    this: Object<'gc>,
+    args: &[Value<'gc>],
+) -> Result<Value<'gc>, Error<'gc>> {
+    // TODO This currently uses screen_position_to_index, which is inaccurate, because:
+    //   1. getCharIndexAtPoint should return -1 when clicked outside of a character,
+    //   2. screen_position_to_index returns caret index, not clicked character index.
+    //   Currently, it is difficult to prove accuracy of this method, as at the time
+    //   of writing this comment, text layout behaves differently compared to Flash.
+    //   However, the current implementation is good enough to make some SWFs work.
+    avm2_stub_method!(
+        activation,
+        "flash.text.TextField",
+        "getCharIndexAtPoint",
+        "inaccurate char index detection"
+    );
+
+    let Some(this) = this
+        .as_display_object()
+        .and_then(|this| this.as_edit_text())
+    else {
+        return Ok(Value::Undefined);
+    };
+
+    let x = args.get_f64(activation, 0)?;
+    let y = args.get_f64(activation, 1)?;
+
+    if let Some(index) = this.screen_position_to_index(Point::from_pixels(x, y)) {
+        Ok(index.into())
+    } else {
+        Ok(Value::Number(-1f64))
+    }
+}
+
+pub fn get_line_index_at_point<'gc>(
+    activation: &mut Activation<'_, 'gc>,
+    this: Object<'gc>,
+    args: &[Value<'gc>],
+) -> Result<Value<'gc>, Error<'gc>> {
+    // TODO This currently uses screen_position_to_index, but it should calculate
+    //   the line index using only line data, without taking into account characters.
+    //   Currently, it is difficult to prove accuracy of this method, as at the time
+    //   of writing this comment, text layout behaves differently compared to Flash.
+    avm2_stub_method!(
+        activation,
+        "flash.text.TextField",
+        "getLineIndexAtPoint",
+        "inaccurate line index detection"
+    );
+
+    let Some(this) = this
+        .as_display_object()
+        .and_then(|this| this.as_edit_text())
+    else {
+        return Ok(Value::Undefined);
+    };
+
+    let x = args.get_f64(activation, 0)?;
+    let y = args.get_f64(activation, 1)?;
+
+    if let Some(index) = this
+        .screen_position_to_index(Point::from_pixels(x, y))
+        .and_then(|index| this.line_index_of_char(index))
+    {
+        Ok(index.into())
+    } else {
+        Ok(Value::Number(-1f64))
+    }
+}