LibGfx: Decouple glyph positions calculation from draw_text_run()

This change separates a part of the `draw_text_run()` function, which
is responsible for calculating the positions for glyphs that need to be
painted, into a separate function called `get_glyph_run()`.

It is a part of the preparation for text run painting using OpenGL,
where we can't immediately blit glyph bitmaps but instead need to
prepare a sequence of quads for them in advance.

Userland/Libraries/LibGfx/Painter.cpp

@@ -1416,48 +1416,14 @@ void Painter::draw_glyph_or_emoji(FloatPoint point, u32 code_point, Font const&
 
 void Painter::draw_glyph_or_emoji(FloatPoint point, Utf8CodePointIterator& it, Font const& font, Color color)
 {
-    u32 code_point = *it;
-    auto next_code_point = it.peek(1);
-
-    ScopeGuard consume_variation_selector = [&, initial_it = it] {
-        static auto const variation_selector = Unicode::property_from_string("Variation_Selector"sv);
-        if (!variation_selector.has_value())
-            return;
-
-        // If we advanced the iterator to consume an emoji sequence, don't look for another variation selector.
-        if (initial_it != it)
-            return;
-
-        // Otherwise, discard one code point if it's a variation selector.
-        if (next_code_point.has_value() && Unicode::code_point_has_property(*next_code_point, *variation_selector))
-            ++it;
-    };
-
-    // NOTE: We don't check for emoji
-    auto font_contains_glyph = font.contains_glyph(code_point);
-    auto check_for_emoji = !font.has_color_bitmaps() && Unicode::could_be_start_of_emoji_sequence(it, font_contains_glyph ? Unicode::SequenceType::EmojiPresentation : Unicode::SequenceType::Any);
-
-    // If the font contains the glyph, and we know it's not the start of an emoji, draw a text glyph.
-    if (font_contains_glyph && !check_for_emoji) {
-        draw_glyph(point, code_point, font, color);
-        return;
+    auto draw_glyph_or_emoji = prepare_draw_glyph_or_emoji(point, it, font);
+    if (draw_glyph_or_emoji.has<DrawGlyph>()) {
+        auto& glyph = draw_glyph_or_emoji.get<DrawGlyph>();
+        draw_glyph(glyph.position, glyph.code_point, *glyph.font, color);
+    } else {
+        auto& emoji = draw_glyph_or_emoji.get<DrawEmoji>();
+        draw_emoji(emoji.position, *emoji.emoji, *emoji.font);
     }
-
-    // If we didn't find a text glyph, or have an emoji variation selector or regional indicator, try to draw an emoji glyph.
-    if (auto const* emoji = Emoji::emoji_for_code_point_iterator(it)) {
-        draw_emoji(point.to_type<int>(), *emoji, font);
-        return;
-    }
-
-    // If that failed, but we have a text glyph fallback, draw that.
-    if (font_contains_glyph) {
-        draw_glyph(point, code_point, font, color);
-        return;
-    }
-
-    // No suitable glyph found, draw a replacement character.
-    dbgln_if(EMOJI_DEBUG, "Failed to find a glyph or emoji for code_point {}", code_point);
-    draw_glyph(point, 0xFFFD, font, color);
 }
 
 void Painter::draw_glyph(IntPoint point, u32 code_point, Color color)
@@ -2473,8 +2439,14 @@ void Painter::draw_text_run(IntPoint baseline_start, Utf8View const& string, Fon
 
 void Painter::draw_text_run(FloatPoint baseline_start, Utf8View const& string, Font const& font, Color color)
 {
-    for_each_glyph_position(baseline_start, string, font, [&](GlyphPosition glyph_position) {
-        draw_glyph_or_emoji(glyph_position.position, glyph_position.it, font, color);
+    for_each_glyph_position(baseline_start, string, font, [&](DrawGlyphOrEmoji glyph_or_emoji) {
+        if (glyph_or_emoji.has<DrawGlyph>()) {
+            auto& glyph = glyph_or_emoji.get<DrawGlyph>();
+            draw_glyph(glyph.position, glyph.code_point, *glyph.font, color);
+        } else {
+            auto& emoji = glyph_or_emoji.get<DrawEmoji>();
+            draw_emoji(emoji.position, *emoji.emoji, *emoji.font);
+        }
     });
 }
 

Userland/Libraries/LibGfx/Path.cpp

@@ -167,13 +167,16 @@ void Path::text(Utf8View text, Font const& font)
         dbgln("Cannot path-ify bitmap fonts!");
         return;
     }
+
     auto& scaled_font = static_cast<ScaledFont const&>(font);
     for_each_glyph_position(
-        last_point(), text, font, [&](GlyphPosition glyph_position) {
-            move_to(glyph_position.position);
-            // FIXME: This does not correctly handle multi-codepoint glyphs (i.e. emojis).
-            auto glyph_id = scaled_font.glyph_id_for_code_point(*glyph_position.it);
-            scaled_font.append_glyph_path_to(*this, glyph_id);
+        last_point(), text, font, [&](DrawGlyphOrEmoji glyph_or_emoji) {
+            if (glyph_or_emoji.has<DrawGlyph>()) {
+                auto& glyph = glyph_or_emoji.get<DrawGlyph>();
+                move_to(glyph.position);
+                auto glyph_id = scaled_font.glyph_id_for_code_point(glyph.code_point);
+                scaled_font.append_glyph_path_to(*this, glyph_id);
+            }
         },
         IncludeLeftBearing::Yes);
 }

Userland/Libraries/LibGfx/TextLayout.cpp

@@ -6,6 +6,10 @@
  */
 
 #include "TextLayout.h"
+#include "Font/Emoji.h"
+#include <AK/Debug.h>
+#include <LibUnicode/CharacterTypes.h>
+#include <LibUnicode/Emoji.h>
 
 namespace Gfx {
 
@@ -192,4 +196,74 @@ DeprecatedString TextLayout::elide_text_from_right(Utf8View text) const
     return text.as_string();
 }
 
+DrawGlyphOrEmoji prepare_draw_glyph_or_emoji(FloatPoint point, Utf8CodePointIterator& it, Font const& font)
+{
+    u32 code_point = *it;
+    auto next_code_point = it.peek(1);
+
+    ScopeGuard consume_variation_selector = [&, initial_it = it] {
+        static auto const variation_selector = Unicode::property_from_string("Variation_Selector"sv);
+        if (!variation_selector.has_value())
+            return;
+
+        // If we advanced the iterator to consume an emoji sequence, don't look for another variation selector.
+        if (initial_it != it)
+            return;
+
+        // Otherwise, discard one code point if it's a variation selector.
+        if (next_code_point.has_value() && Unicode::code_point_has_property(*next_code_point, *variation_selector))
+            ++it;
+    };
+
+    // NOTE: We don't check for emoji
+    auto font_contains_glyph = font.contains_glyph(code_point);
+    auto check_for_emoji = !font.has_color_bitmaps() && Unicode::could_be_start_of_emoji_sequence(it, font_contains_glyph ? Unicode::SequenceType::EmojiPresentation : Unicode::SequenceType::Any);
+
+    // If the font contains the glyph, and we know it's not the start of an emoji, draw a text glyph.
+    if (font_contains_glyph && !check_for_emoji) {
+        return DrawGlyph {
+            .position = point,
+            .code_point = code_point,
+            .font = &font,
+        };
+    }
+
+    // If we didn't find a text glyph, or have an emoji variation selector or regional indicator, try to draw an emoji glyph.
+    if (auto const* emoji = Emoji::emoji_for_code_point_iterator(it)) {
+        return DrawEmoji {
+            .position = point.to_type<int>(),
+            .emoji = emoji,
+            .font = &font,
+        };
+    }
+
+    // If that failed, but we have a text glyph fallback, draw that.
+    if (font_contains_glyph) {
+        return DrawGlyph {
+            .position = point,
+            .code_point = code_point,
+            .font = &font,
+        };
+    }
+
+    // No suitable glyph found, draw a replacement character.
+    dbgln_if(EMOJI_DEBUG, "Failed to find a glyph or emoji for code_point {}", code_point);
+    return DrawGlyph {
+        .position = point,
+        .code_point = 0xFFFD,
+        .font = &font,
+    };
+}
+
+Vector<DrawGlyphOrEmoji> get_glyph_run(FloatPoint baseline_start, Utf8View const& string, Font const& font, IncludeLeftBearing include_left_bearing)
+{
+    Vector<DrawGlyphOrEmoji> glyphs_or_emojis;
+    for_each_glyph_position(
+        baseline_start, string, font, [&](auto glyph_or_emoji) {
+            glyphs_or_emojis.append(glyph_or_emoji);
+        },
+        include_left_bearing);
+    return glyphs_or_emojis;
+}
+
 }

Userland/Libraries/LibGfx/TextLayout.h

@@ -75,23 +75,33 @@ enum class IncludeLeftBearing {
     No
 };
 
-struct GlyphPosition {
+struct DrawGlyph {
     FloatPoint position;
-    float glyph_width;
-    AK::Utf8CodePointIterator& it;
+    u32 code_point;
+    Font const* font;
 };
 
+struct DrawEmoji {
+    IntPoint position;
+    Gfx::Bitmap const* emoji;
+    Font const* font;
+};
+
+using DrawGlyphOrEmoji = Variant<DrawGlyph, DrawEmoji>;
+
+Variant<DrawGlyph, DrawEmoji> prepare_draw_glyph_or_emoji(FloatPoint point, Utf8CodePointIterator& it, Font const& font);
+
 template<typename Callback>
-void for_each_glyph_position(FloatPoint start, Utf8View text, Font const& font, Callback callback, IncludeLeftBearing include_left_bearing = IncludeLeftBearing::No)
+void for_each_glyph_position(FloatPoint baseline_start, Utf8View string, Font const& font, Callback callback, IncludeLeftBearing include_left_bearing = IncludeLeftBearing::No)
 {
     float space_width = font.glyph_width(' ') + font.glyph_spacing();
 
     u32 last_code_point = 0;
 
-    auto point = start;
+    auto point = baseline_start;
     point.translate_by(0, -font.pixel_metrics().ascent);
 
-    for (auto code_point_iterator = text.begin(); code_point_iterator != text.end(); ++code_point_iterator) {
+    for (auto code_point_iterator = string.begin(); code_point_iterator != string.end(); ++code_point_iterator) {
         auto code_point = *code_point_iterator;
         if (should_paint_as_space(code_point)) {
             point.translate_by(space_width, 0);
@@ -106,18 +116,19 @@ void for_each_glyph_position(FloatPoint start, Utf8View text, Font const& font,
         auto it = code_point_iterator; // The callback function will advance the iterator, so create a copy for this lookup.
         auto glyph_width = font.glyph_or_emoji_width(it) + font.glyph_spacing();
 
-        auto glyph_point = point;
-        if (include_left_bearing == IncludeLeftBearing::Yes)
-            glyph_point += FloatPoint(font.glyph_left_bearing(code_point), 0);
+        auto glyph_or_emoji = prepare_draw_glyph_or_emoji(point, code_point_iterator, font);
+        if (include_left_bearing == IncludeLeftBearing::Yes) {
+            if (glyph_or_emoji.has<DrawGlyph>())
+                glyph_or_emoji.get<DrawGlyph>().position += FloatPoint(font.glyph_left_bearing(code_point), 0);
+        }
 
-        callback(GlyphPosition {
-            .position = glyph_point,
-            .glyph_width = glyph_width,
-            .it = code_point_iterator });
+        callback(glyph_or_emoji);
 
         point.translate_by(glyph_width, 0);
         last_code_point = code_point;
     }
 }
 
+Vector<DrawGlyphOrEmoji> get_glyph_run(FloatPoint baseline_start, Utf8View const& string, Font const& font, IncludeLeftBearing include_left_bearing = IncludeLeftBearing::No);
+
 }