mirror of https://github.com/koreader/koreader
[RTL UI] adds bidi.lua, bootstrap UI mirroring with RTL languages
Set default language (for Harfbuzz to pick up localized glyphs in a font), default text direction, and UI element mirroring depending on the UI language.pull/5680/head
poire-z
4 years ago
parent
08a5275984
commit
866c9571df
@ -0,0 +1,189 @@
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--[[--
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Bidirectional text and UI mirroring setup and helpers.
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There are 2 concepts we attempt to handle:
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- Text direction: Left-To-Right (LTR) or Right-To-Left (RTL)
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- UI elements mirroring: not-mirrored, or mirrored
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These 2 concepts are somehow orthogonal to each other in
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their implementation, even if in the real world there are
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only 2 valid combinations:
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- LTR and not-mirrored: for western languages, CJK, Indic...
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- RTL and mirrored: for Arabic, Hebrew, Farsi and a few others.
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Text direction is handled by the libkoreader-xtext.so C module,
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and the TextWidget and TextBoxWidget widgets that handle text
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aligment. We just need here to set the default global paragraph
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direction (that widgets can override if needed).
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UI mirroring is to be handled by our widget themselves, with the
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help of a few functions defined here.
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Fortunately, low level widgets like LeftContainer, RightContainer,
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FrameContainer, HorizontalGroup, OverlapGroup... will do most of
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the work.
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But some care must be taken in other widgets and apps when:
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- some arrow symbols are used (for next, previous, first, last...):
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they might need to be swapped, or some alternative symbols or
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images can be used.
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- some geometry arithmetic is done (e.g. detecting if a tap is on the
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right part of screen, to go forward), which need to be adapted/reversed.
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- handling left or right swipe, whose action might need to be reversed
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- some TextBoxWidget/InputText might need to be forced to be LTR (when
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showing HTML or CSS code, or entering URLs, path...)
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Some overview at:
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https://material.io/design/usability/bidirectionality.html
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]]
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local Language = require("ui/language")
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local _ = require("gettext")
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local Bidi = {
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_mirrored_ui_layout = false,
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_rtl_ui_text = false,
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}
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-- Setup UI mirroring and RTL text for UI language
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function Bidi.setup(lang)
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local is_rtl = Language:isLanguageRTL(lang)
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-- Mirror UI if language is RTL
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Bidi._mirrored_ui_layout = is_rtl
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-- Unless requested not to (or requested mirroring with LTR language)
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if G_reader_settings:isTrue("dev_reverse_ui_layout_mirroring") then
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Bidi._mirrored_ui_layout = not Bidi._mirrored_ui_layout
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end
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-- Xtext default language and direction
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if G_reader_settings:nilOrTrue("use_xtext") then
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local xtext = require("libs/libkoreader-xtext")
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-- Text direction should normally not follow ui mirroring
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-- lang override (so that Arabic is still right aligned
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-- when one wants the UI layout LTR). But allow it to
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-- be independantly reversed (for testing UI mirroring
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-- with english text right aligned).
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if G_reader_settings:isTrue("dev_reverse_ui_text_direction") then
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is_rtl = not is_rtl
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end
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Bidi._rtl_ui_text = is_rtl
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xtext.setDefaultParaDirection(is_rtl)
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-- Text language: this helps picking localized glyphs from the
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-- font (eg. ideographs shaped differently for Japanese vs
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-- Simplified Chinese vs Traditional Chinese).
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-- Allow overriding xtext language rules from main UI language
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-- (eg. English UI, with French line breaking rules)
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local alt_lang = G_reader_settings:readSetting("xtext_alt_lang") or lang
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if alt_lang then
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xtext.setDefaultLang(alt_lang)
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end
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end
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-- Optimise Bidi.default and Bidi.wrap by aliasing them to the right wrappers
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if Bidi._rtl_ui_text then
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Bidi.default = Bidi.rtl
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Bidi.wrap = Bidi.rtl
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else
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Bidi.default = Bidi.ltr
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Bidi.wrap = Bidi.noop
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end
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end
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-- Use this function in widgets to check if UI elements mirroring
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-- is to be done
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function Bidi.mirroredUILayout()
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return Bidi._mirrored_ui_layout
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end
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-- This function might only be useful in some rare cases (RTL text
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-- is handled directly by TextWidget and TextBoxWidget)
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function Bidi.rtlUIText()
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return Bidi._rtl_ui_text
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end
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-- Small helper to mirror gesture directions
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local mirrored_directions = {
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east = "west",
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west = "east",
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northeast = "northwest",
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northwest = "northeast",
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southeast = "southwest",
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southwest = "southeast",
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}
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function Bidi.flipDirectionIfMirroredUILayout(direction)
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if Bidi._mirrored_ui_layout then
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return mirrored_directions[direction] or direction
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end
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return direction
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end
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function Bidi.flipIfMirroredUILayout(bool)
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if Bidi._mirrored_ui_layout then
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return not bool
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end
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return bool
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end
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-- Wrap provided text with bidirectionality control characters, see:
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-- http://unicode.org/reports/tr9/#Markup_And_Formatting
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-- https://www.w3.org/International/questions/qa-bidi-unicode-controls.en
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-- https://www.w3.org/International/articles/inline-bidi-markup/
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-- This works only when use_xtext=true: these characters are used
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-- by FriBidi for correct char visual ordering, and later stripped
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-- by Harfbuzz.
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-- When use_xtext=false, these characters are considered as normal
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-- characters, and would be printed. Fortunately, most fonts know them
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-- and provide an invisible glyph of zero-width - except FreeSans and
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-- FreeSerif which provide a real glyph (a square with "LRI" inside)
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-- which would be an issue and would need stripping. But as these
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-- Free fonts are only used as fallback fonts, and the invisible glyphs
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-- will have been found in the previous fonts, we don't need to.
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local LRI = "\xE2\x81\xA6" -- U+2066 LRI / LEFT-TO-RIGHT ISOLATE
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local RLI = "\xE2\x81\xA7" -- U+2067 RLI / RIGHT-TO-LEFT ISOLATE
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local FSI = "\xE2\x81\xA8" -- U+2068 FSI / FIRST STRONG ISOLATE
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local PDI = "\xE2\x81\xA9" -- U+2069 PDI / POP DIRECTIONAL ISOLATE
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function Bidi.ltr(text)
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return string.format("%s%s%s", LRI, text, PDI)
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end
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function Bidi.rtl(text) -- should hardly be needed
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return string.format("%s%s%s", RLI, text, PDI)
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end
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function Bidi.auto(text) -- from first strong character
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return string.format("%s%s%s", FSI, text, PDI)
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end
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function Bidi.default(text) -- default direction
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return Bidi._rtl_ui_text and Bidi.rtl(text) or Bidi.ltr(text)
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end
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function Bidi.noop(text) -- no wrap
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return text
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end
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-- Helper for concatenated string bits of numbers an symbols (like
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-- our reader footer) to keep them ordered in RTL UI (to not have
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-- a letter B for battery make the whole string considered LTR).
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-- Note: it will be replaced and aliased to Bidi.noop or Bidi.rtl
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-- by Bibi.setup() as an optimisation
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function Bidi.wrap(text)
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return Bidi._rtl_ui_text and Bidi.rtl(text) or text
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end
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-- See at having GetText_mt.__call() wrap untranslated strings in Bidi.ltr()
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-- so they are fully displayed LTR.
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-- Use these specific wrappers when the wrapped content type is known
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-- (so we can easily switch to use rtl() if RTL readers prefer filenames
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-- shown as real RTL).
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-- Note: when the filename or path are standalone in a TextWidget, it's
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-- better to use "para_direction_rtl = false" without any wrapping.
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Bidi.filename = Bidi.ltr
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Bidi.directory = Bidi.ltr
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Bidi.path = Bidi.ltr
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Bidi.url = Bidi.ltr
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return Bidi
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