TextBoxWidget: allow showing bits of text in bold

Allow for embedding "tags" (invalid Unicode codepoints)
in the text string to trigger some text formatting:
for now only bolding some parts of text is possible.

Use it with fulltext search "all results" to highlight the
matched word (instead of the previously used brackets).

frontend/apps/reader/modules/readersearch.lua

@@ -7,6 +7,7 @@ local InputDialog = require("ui/widget/inputdialog")
 local Menu = require("ui/widget/menu")
 local Notification = require("ui/widget/notification")
 local SpinWidget = require("ui/widget/spinwidget")
+local TextBoxWidget = require("ui/widget/textboxwidget")
 local UIManager = require("ui/uimanager")
 local Utf8Proc = require("ffi/utf8proc")
 local WidgetContainer = require("ui/widget/container/widgetcontainer")
@@ -525,14 +526,17 @@ function ReaderSearch:showFindAllResults(not_cached)
             if item.matched_word_suffix then
                 word = word .. item.matched_word_suffix
             end
+            -- Make this word bolder, using Poor Text Formatting provided by TextBoxWidget
+            -- (we know this text ends up in a TextBoxWidget).
+            local text = TextBoxWidget.PTF_BOLD_START .. word .. TextBoxWidget.PTF_BOLD_END
             -- append context before and after the word
-            local text = "【" .. word .. "】"
             if item.prev_text then
                 text = item.prev_text .. text
             end
             if item.next_text then
                 text = text .. item.next_text
             end
+            text = TextBoxWidget.PTF_HEADER .. text -- enable handling of our bold tags
             item.text = text
             item.mandatory = self.ui.bookmark:getBookmarkPageString(item.start)
         end

frontend/document/koptinterface.lua

@@ -12,6 +12,7 @@ local FFIUtil = require("ffi/util")
 local Geom = require("ui/geometry")
 local KOPTContext = require("ffi/koptcontext")
 local Persist = require("persist")
+local TextBoxWidget = require("ui/widget/textboxwidget")
 local TileCacheItem = require("document/tilecacheitem")
 local Utf8Proc = require("ffi/utf8proc")
 local logger = require("logger")
@@ -1510,15 +1511,18 @@ function KoptInterface:findAllText(doc, pattern, case_insensitive, nb_context_wo
                         i_next, j_next = i, j
                     end
                 end
-                text = "【" .. table.concat(text, " ") .. "】"
+                -- Make this word bolder, using Poor Text Formatting provided by TextBoxWidget
+                -- (we know this text ends up in a TextBoxWidget).
+                text = TextBoxWidget.PTF_BOLD_START .. table.concat(text, " ") .. TextBoxWidget.PTF_BOLD_END
                 local prev_text = get_prev_text(text_boxes, i_prev, j_prev, nb_context_words)
                 if prev_text then
-                    text = prev_text .. text
+                    text = prev_text .. " " .. text
                 end
                 local next_text = get_next_text(text_boxes, i_next, j_next, nb_context_words)
                 if next_text then
-                    text = text .. next_text
+                    text = text .. " " .. next_text
                 end
+                text = TextBoxWidget.PTF_HEADER .. text -- enable handling of our bold tags
                 res_item.text = text
                 table.insert(res, res_item)
                 if #res == max_hits then

frontend/ui/rendertext.lua

@@ -289,17 +289,25 @@ end
 -- @int glyph index
 -- @bool[opt=false] bold whether the glyph should be artificially boldened
 -- @treturn glyph
-function RenderText:getGlyphByIndex(face, glyphindex, bold)
+function RenderText:getGlyphByIndex(face, glyphindex, bold, bolder)
     if face.is_real_bold then
         bold = false -- don't embolden glyphs already bold
     end
-    local hash = "xglyph|"..face.hash.."|"..glyphindex.."|"..(bold and 1 or 0)
+    local hash = "xglyph|"..face.hash.."|"..glyphindex.."|"..(bold and 1 or 0)..(bolder and "x" or "")
     local glyph = GlyphCache:check(hash)
     if glyph then
         -- cache hit
         return glyph
     end
-    local rendered_glyph = face.ftsize:renderGlyphByIndex(glyphindex, bold and face.embolden_half_strength)
+    local embolden_strength
+    if bold or bolder then
+        embolden_strength = face.embolden_half_strength
+        if bolder then
+            -- Even if not bold, get it bolder than the strength we'd use for bold
+            embolden_strength = embolden_strength * 1.5
+        end
+    end
+    local rendered_glyph = face.ftsize:renderGlyphByIndex(glyphindex, embolden_strength)
     if not rendered_glyph then
         logger.warn("error rendering glyph (glyphindex=", glyphindex, ") for face", face)
         return

frontend/ui/widget/textboxwidget.lua

@@ -110,6 +110,17 @@ local TextBoxWidget = InputContainer:extend{
 
     -- for internal use
     for_measurement_only = nil, -- When the widget is a one-off used to compute text height
+
+    -- Some Poor Text Formatting (PTF, not not to be confused with Richer RTF :)) can be done
+    -- by embedding some chars in self.text (these codepoints are not part of Unicode, so
+    -- hopefully not present naturally in any provided self.text).
+    PTF_HEADER = "\u{FFF1}", -- should be put at start of 'text' to indicate we may find other PTF_ chars
+    PTF_BOLD_START = "\u{FFF2}", -- start a sequence of bold chars
+    PTF_BOLD_END = "\u{FFF3}",   -- end a sequence of bold chars
+    _ptf_char_is_bold = nil,
+        -- This uses fake/synthetic bold, making each glyph bolder without modifying advance.
+        -- Some other possible formatting we could implement is different alignment (center,
+        -- right) of some lines in the provided text.
 }
 
 function TextBoxWidget:init()
@@ -154,6 +165,41 @@ function TextBoxWidget:init()
         self.text_height = self.lines_per_page * self.line_height_px
     end
 
+    -- Check for Poor Text Formatting
+    if not self.charlist and self.text and type(self.text) == "string"
+            and self.text:sub(1, #TextBoxWidget.PTF_HEADER) == TextBoxWidget.PTF_HEADER then
+        -- Support for very simple text styling (bold only for now)
+        self._ptf_char_is_bold = {}
+        -- Alas, we can't let any of our flag characters be fed to xtext (even with ASCII control
+        -- chars, it would give them a width, which would result at best in spurious added spacing).
+        -- So, split text into a table of chars, filter our flags out keeping track of where they
+        -- start and end bold, and rebuild self.text without them.
+        local charlist = util.splitToChars(self.text)
+        table.remove(charlist, 1)
+        local is_bold = false
+        local len = #charlist
+        local i = 1
+        while i <= len do
+            local ch = charlist[i]
+            if ch == TextBoxWidget.PTF_BOLD_START then
+                is_bold = true
+                table.remove(charlist, i)
+                len = len - 1
+            elseif ch == TextBoxWidget.PTF_BOLD_END then
+                is_bold = false
+                table.remove(charlist, i)
+                len = len - 1
+            else
+                if is_bold then
+                    self._ptf_char_is_bold[i] = true
+                end
+                i = i + 1
+            end
+        end
+        self.text = table.concat(charlist, "")
+        charlist = nil -- luacheck: no unused
+    end
+
     self:_computeTextDimensions()
     self:_updateLayout()
     if self.editable then
@@ -822,7 +868,8 @@ function TextBoxWidget:_renderText(start_row_idx, end_row_idx)
                 for _, xglyph in ipairs(line.xglyphs) do
                     if not xglyph.no_drawing then
                         local face = self.face.getFallbackFont(xglyph.font_num) -- callback (not a method)
-                        local glyph = RenderText:getGlyphByIndex(face, xglyph.glyph, self.bold)
+                        local bolder = self._ptf_char_is_bold and self._ptf_char_is_bold[xglyph.text_index] or false
+                        local glyph = RenderText:getGlyphByIndex(face, xglyph.glyph, self.bold, bolder)
                         local color = self.fgcolor
                         if self._alt_color_for_rtl then
                             color = xglyph.is_rtl and Blitbuffer.COLOR_DARK_GRAY or Blitbuffer.COLOR_BLACK