LibDraw: Add emoji drawing support to Painter

From here on, all strings displayed to the user are expected to
be encoded as UTF-8. The next few commits will deal with a few
existing places where this requirement is currently violated.

https://github.com/SerenityOS/serenity/issues/490

Libraries/LibDraw/Painter.cpp

@@ -1,6 +1,7 @@
 #include "Painter.h"
 #include "Font.h"
 #include "GraphicsBitmap.h"
+#include "Emoji.h"
 #include <AK/Assertions.h>
 #include <AK/StdLibExtras.h>
 #include <AK/StringBuilder.h>
@@ -8,6 +9,7 @@
 #include <math.h>
 #include <stdio.h>
 #include <unistd.h>
+#include <AK/Utf8View.h>
 
 #pragma GCC optimize("O3")
 
@@ -554,34 +556,69 @@ void Painter::draw_scaled_bitmap(const Rect& a_dst_rect, const GraphicsBitmap& s
     draw_bitmap(point, font.glyph_bitmap(ch), color);
 }
 
-void Painter::draw_text_line(const Rect& a_rect, const StringView& text, const Font& font, TextAlignment alignment, Color color, TextElision elision)
+void Painter::draw_emoji(const Point& point, const Emoji& emoji, const Font& font)
+{
+    if (!font.is_fixed_width())
+        blit(point, emoji.bitmap(), emoji.bitmap().rect());
+    else {
+        Rect dst_rect {
+            point.x(),
+            point.y(),
+            font.glyph_width('x'),
+            font.glyph_height()
+        };
+        draw_scaled_bitmap(dst_rect, emoji.bitmap(), emoji.bitmap().rect());
+    }
+}
+
+void Painter::draw_glyph_or_emoji(const Point& point, u32 codepoint, const Font& font, Color color)
+{
+    if (codepoint < 256) {
+        // This looks like a regular character.
+        draw_glyph(point, (char)codepoint, font, color);
+        return;
+    }
+
+    // Perhaps it's an emoji?
+    const Emoji* emoji = Emoji::emoji_for_codepoint(codepoint);
+    if (emoji == nullptr) {
+        dbg() << "Failed to find an emoji for codepoint " << codepoint;
+        draw_glyph(point, '?', font, color);
+        return;
+    }
+
+    draw_emoji(point, *emoji, font);
+}
+
+void Painter::draw_text_line(const Rect& a_rect, const Utf8View& text, const Font& font, TextAlignment alignment, Color color, TextElision elision)
 {
     auto rect = a_rect;
-    StringView final_text(text);
+    Utf8View final_text(text);
     String elided_text;
     if (elision == TextElision::Right) {
         int text_width = font.width(final_text);
         if (font.width(final_text) > rect.width()) {
             int glyph_spacing = font.glyph_spacing();
-            int new_length = 0;
+            int byte_offset = 0;
             int new_width = font.width("...");
             if (new_width < text_width) {
-                for (int i = 0; i < final_text.length(); ++i) {
-                    int glyph_width = font.glyph_width(final_text.characters_without_null_termination()[i]);
+                for (auto it = final_text.begin(); it != final_text.end(); ++it) {
+                    u32 codepoint = *it;
+                    int glyph_width = font.glyph_or_emoji_width(codepoint);
                     // NOTE: Glyph spacing should not be added after the last glyph on the line,
                     //       but since we are here because the last glyph does not actually fit on the line,
                     //       we don't have to worry about spacing.
                     int width_with_this_glyph_included = new_width + glyph_width + glyph_spacing;
                     if (width_with_this_glyph_included > rect.width())
                         break;
-                    ++new_length;
+                    byte_offset = final_text.byte_offset_of(it);
                     new_width += glyph_width + glyph_spacing;
                 }
                 StringBuilder builder;
-                builder.append(StringView(final_text.characters_without_null_termination(), new_length));
+                builder.append(final_text.substring_view(0, byte_offset).as_string());
                 builder.append("...");
                 elided_text = builder.to_string();
-                final_text = elided_text;
+                final_text = Utf8View { elided_text };
             }
         }
     }
@@ -604,14 +641,13 @@ void Painter::draw_text_line(const Rect& a_rect, const StringView& text, const F
     auto point = rect.location();
     int space_width = font.glyph_width(' ') + font.glyph_spacing();
 
-    for (ssize_t i = 0; i < final_text.length(); ++i) {
-        char ch = final_text.characters_without_null_termination()[i];
-        if (ch == ' ') {
+    for (u32 codepoint : final_text) {
+        if (codepoint == ' ') {
             point.move_by(space_width, 0);
             continue;
         }
-        draw_glyph(point, ch, font, color);
-        point.move_by(font.glyph_width(ch) + font.glyph_spacing(), 0);
+        draw_glyph_or_emoji(point, codepoint, font, color);
+        point.move_by(font.glyph_or_emoji_width(codepoint) + font.glyph_spacing(), 0);
     }
 }
 
@@ -620,22 +656,25 @@ void Painter::draw_text(const Rect& rect, const StringView& text, TextAlignment
     draw_text(rect, text, font(), alignment, color, elision);
 }
 
-void Painter::draw_text(const Rect& rect, const StringView& text, const Font& font, TextAlignment alignment, Color color, TextElision elision)
+void Painter::draw_text(const Rect& rect, const StringView& raw_text, const Font& font, TextAlignment alignment, Color color, TextElision elision)
 {
-    Vector<StringView, 32> lines;
+    Utf8View text { raw_text };
+    Vector<Utf8View, 32> lines;
 
     int start_of_current_line = 0;
-    for (int i = 0; i < text.length(); ++i) {
-        auto ch = text[i];
-        if (ch == '\n') {
-            lines.append(text.substring_view(start_of_current_line, i - start_of_current_line));
-            start_of_current_line = i + 1;
-            continue;
+    for (auto it = text.begin(); it != text.end(); ++it) {
+        u32 codepoint = *it;
+        if (codepoint == '\n') {
+            int byte_offset = text.byte_offset_of(it);
+            Utf8View line = text.substring_view(start_of_current_line, byte_offset - start_of_current_line);
+            lines.append(line);
+            start_of_current_line = byte_offset + 1;
         }
     }
 
-    if (start_of_current_line != text.length()) {
-        lines.append(text.substring_view(start_of_current_line, text.length() - start_of_current_line));
+    if (start_of_current_line != text.byte_length()) {
+        Utf8View line = text.substring_view(start_of_current_line, text.byte_length() - start_of_current_line);
+        lines.append(line);
     }
 
     static const int line_spacing = 4;