Add IME support (#991)

data/core/ime.lua

@@ -0,0 +1,83 @@
+local core = require "core"
+
+local ime = { }
+
+function ime.reset()
+  ime.editing = false
+end
+
+---Convert from utf-8 offset and length (from SDL) to byte offsets
+---@param text string @Textediting string
+---@param start integer @0-based utf-8 offset of the starting position of the selection
+---@param length integer @Size of the utf-8 length of the selection
+function ime.ingest(text, start, length)
+  if #text == 0 then
+    -- finished textediting
+    ime.reset()
+    return "", 0, 0
+  end
+
+  ime.editing = true
+
+  if start < 0 then
+    -- we assume no selection and caret at the end
+    return text, #text, 0
+  end
+
+  -- start is 0-based, so we use start + 1
+  local start_byte = utf8.offset(text, start + 1)
+  if not start_byte then
+    -- bad start offset
+    -- we assume it meant the last byte of the text
+    start_byte = #text
+  else
+    start_byte = math.min(start_byte - 1, #text)
+  end
+
+  if length < 0 then
+    -- caret only
+    return text, start_byte, 0
+  end
+
+  local end_byte = utf8.offset(text, start + length + 1)
+  if not end_byte or end_byte - 1 < start_byte then
+    -- bad length, assume caret only
+    return text, start_byte, 0
+  end
+
+  end_byte = math.min(end_byte - 1, #text)
+  return text, start_byte, end_byte - start_byte
+end
+
+---Forward the given textediting SDL event data to Views.
+---@param text string @Textediting string
+---@param start integer @0-based utf-8 offset of the starting position of the selection
+---@param length integer @Size of the utf-8 length of the selection
+function ime.on_text_editing(text, start, length, ...)
+  if ime.editing or #text > 0 then
+    core.root_view:on_ime_text_editing(ime.ingest(text, start, length, ...))
+  end
+end
+
+---Stop IME composition.
+---Might not completely work on every platform.
+function ime.stop()
+  if ime.editing then
+    -- SDL_ClearComposition for now doesn't work everywhere
+    system.clear_ime()
+    ime.on_text_editing("", 0, 0)
+  end
+end
+
+---Set the bounding box of the text pertaining the IME.
+---The IME will draw its interface based on this info.
+---@param x number
+---@param y number
+---@param w number
+---@param h number
+function ime.set_location(x, y, w, h)
+  system.set_text_input_rect(x, y, w, h)
+end
+
+ime.reset()
+return ime