LibWeb: Add SVG::ViewBox to represent SVG view boxes

This also comes with a simple little parsing helper. :^)

Userland/Libraries/LibWeb/SVG/ViewBox.cpp

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/CharacterTypes.h>
+#include <AK/GenericLexer.h>
+#include <AK/Optional.h>
+#include <AK/StringView.h>
+#include <LibWeb/SVG/ViewBox.h>
+
+namespace Web::SVG {
+
+Optional<ViewBox> try_parse_view_box(StringView string)
+{
+    // FIXME: This should handle all valid viewBox values.
+
+    GenericLexer lexer(string);
+
+    enum State {
+        MinX,
+        MinY,
+        Width,
+        Height,
+    };
+    int state { State::MinX };
+    ViewBox view_box;
+
+    while (!lexer.is_eof()) {
+        lexer.consume_while([](auto ch) { return is_ascii_space(ch); });
+        auto token = lexer.consume_until([](auto ch) { return is_ascii_space(ch) && ch != ','; });
+        auto maybe_number = token.to_int();
+        if (!maybe_number.has_value())
+            return {};
+        switch (state) {
+        case State::MinX:
+            view_box.min_x = maybe_number.value();
+            break;
+        case State::MinY:
+            view_box.min_y = maybe_number.value();
+            break;
+        case State::Width:
+            view_box.width = maybe_number.value();
+            break;
+        case State::Height:
+            view_box.height = maybe_number.value();
+            break;
+        default:
+            return {};
+        }
+        state += 1;
+    }
+
+    return view_box;
+}
+
+}