More work on the variable-width font support.

Katica is now the default system font, and it looks quite nice. :^)
I'm gonna need to refine the GTextBox movement stuff eventually,
but it works well-enough for basic editing now.

LibGUI/GTextBox.cpp

@@ -21,12 +21,58 @@ void GTextBox::set_text(const String& text)
         return;
     m_text = text;
     m_cursor_position = m_text.length();
+    scroll_cursor_into_view(HorizontalDirection::Right);
     update();
 }
 
+void GTextBox::scroll_cursor_into_view(HorizontalDirection direction)
+{
+    if (visible_content_rect().contains(cursor_content_position()))
+        return;
+    int total_text_width = font().width(m_text);
+    dbgprintf("total_text_width = %d, visible_content width = %d\n", total_text_width, visible_content_rect().width());
+    if (total_text_width < visible_content_rect().width()) {
+        m_scroll_offset = 0;
+        return;
+    }
+    if (direction == HorizontalDirection::Left) {
+        dbgprintf("Left, orig offset = %d\n", m_scroll_offset);
+        m_scroll_offset = cursor_content_position().x();
+        int offset_into_visible = m_scroll_offset - visible_content_rect().x();
+        if (offset_into_visible < font().glyph_width(' '))
+            m_scroll_offset -= width() / 2;
+    } else {
+        m_scroll_offset = cursor_content_position().x() - visible_content_rect().width();
+        dbgprintf("Right, orig offset = %d\n", m_scroll_offset);
+        int offset_into_visible = m_scroll_offset - visible_content_rect().x();
+        if (offset_into_visible > width() / 4) {
+            dbgprintf("Right, adjust offset = %d\n", m_scroll_offset);
+            m_scroll_offset += width() / 2;
+        }
+    }
+    if (m_scroll_offset < 0)
+        m_scroll_offset = 0;
+    if (m_scroll_offset > total_text_width)dbgprintf("Right, adjust offset = %d\n", m_scroll_offset);
+        m_scroll_offset = total_text_width - width();
+}
+
+Rect GTextBox::visible_content_rect() const
+{
+    if (rect().is_empty())
+        return { };
+    return { m_scroll_offset, 0, rect().shrunken(6, 6).width(), rect().shrunken(6, 6).height() };
+}
+
+Point GTextBox::cursor_content_position() const
+{
+    int x = 0;
+    for (int i = 0; i < m_cursor_position; ++i)
+        x += font().glyph_width(m_text[i]) + font().glyph_spacing();
+    return { x, 0 };
+}
+
 void GTextBox::paint_event(GPaintEvent& event)
 {
-    ASSERT(font().is_fixed_width());
     Painter painter(*this);
     painter.set_clip_rect(event.rect());
 
@@ -39,27 +85,25 @@ void GTextBox::paint_event(GPaintEvent& event)
     Rect inner_rect = rect();
     inner_rect.shrink(6, 6);
 
-    ssize_t max_chars_to_paint = inner_rect.width() / font().min_glyph_width();
+    painter.set_clip_rect(inner_rect);
+    painter.translate(-m_scroll_offset, 0);
 
-    int first_visible_char = max((int)m_cursor_position - (int)max_chars_to_paint, 0);
-    ssize_t chars_to_paint = min(m_text.length() - first_visible_char, max_chars_to_paint);
     int y = inner_rect.center().y() - font().glyph_height() / 2;    
-    int space_width = font().glyph_width(' ');
+    int space_width = font().glyph_width(' ') + font().glyph_spacing();
     int x = inner_rect.x();
 
-    for (ssize_t i = 0; i < chars_to_paint; ++i) {
-        char ch = m_text[first_visible_char + i];
+    for (int i = 0; i < m_text.length(); ++i) {
+        char ch = m_text[i];
         if (ch == ' ') {
             x += space_width;
             continue;
         }
         painter.draw_glyph({x, y}, ch, Color::Black);
-        x += font().glyph_width(ch);
+        x += font().glyph_width(ch) + font().glyph_spacing();
     }
 
     if (is_focused() && m_cursor_blink_state) {
-        int visible_cursor_position = m_cursor_position - first_visible_char;
-        Rect cursor_rect(inner_rect.x() + visible_cursor_position * font().glyph_width('x'), inner_rect.y(), 1, inner_rect.height());
+        Rect cursor_rect(inner_rect.x() + cursor_content_position().x(), inner_rect.y(), 1, inner_rect.height());
         painter.fill_rect(cursor_rect, foreground_color());
     }
 }
@@ -76,6 +120,7 @@ void GTextBox::handle_backspace()
     if (m_text.length() == 1) {
         m_text = String::empty();
         m_cursor_position = 0;
+        m_scroll_offset = 0;
         if (on_change)
             on_change(*this);
         update();
@@ -90,6 +135,7 @@ void GTextBox::handle_backspace()
 
     m_text = move(new_text);
     --m_cursor_position;
+    scroll_cursor_into_view(HorizontalDirection::Left);
     if (on_change)
         on_change(*this);
     update();
@@ -99,14 +145,18 @@ void GTextBox::keydown_event(GKeyEvent& event)
 {
     switch (event.key()) {
     case KeyCode::Key_Left:
-        if (m_cursor_position)
+        if (m_cursor_position) {
             --m_cursor_position;
+            scroll_cursor_into_view(HorizontalDirection::Left);
+        }
         m_cursor_blink_state = true;
         update();
         return;
     case KeyCode::Key_Right:
-        if (m_cursor_position < m_text.length())
+        if (m_cursor_position < m_text.length()) {
             ++m_cursor_position;
+            scroll_cursor_into_view(HorizontalDirection::Right);
+        }
         m_cursor_blink_state = true;
         update();
         return;
@@ -130,6 +180,7 @@ void GTextBox::keydown_event(GKeyEvent& event)
 
         m_text = move(new_text);
         ++m_cursor_position;
+        scroll_cursor_into_view(HorizontalDirection::Right);
         if (on_change)
             on_change(*this);
         update();
@@ -156,3 +207,8 @@ void GTextBox::focusout_event(GEvent&)
 {
     stop_timer();
 }
+
+void GTextBox::resize_event(GResizeEvent&)
+{
+    scroll_cursor_into_view(HorizontalDirection::Right);
+}