#72 Possible attribute formatter implementation (#73)

src/backend/BackendSVG.cpp

@@ -91,13 +91,15 @@ void BackendSVG::rect(const bfloat2_t &x, const float r) noexcept {
   const auto &delta = x.delta();
   vfloat2_t min = x.min();
 
+  m_out << "<rect ";
+
   // Position, width and height
-  m_out << "<rect x=\"" << min[0] << "\" y=\"" << min[1] << "\" width=\""
-        << delta[0] << "\" height=\"" << delta[1] << "\" ";
+  m_out << m_att("x", min[0]) << m_att("y", min[1]) << m_att("width", delta[0])
+        << m_att("height", delta[1]);
 
   // Rounding corners
   if (r > 0.f) {
-    m_out << "rx=\"" << r << "\" ry=\"" << r << "\" ";
+    m_out << m_att("rx", r) << m_att("ry", r);
   }
 
   // Styling
@@ -115,8 +117,8 @@ void BackendSVG::rect(const bfloat2_t &x, const float r) noexcept {
 
 void BackendSVG::circle_begin(const vfloat2_t &centre, const float r) noexcept {
 
-  m_out << "<circle cx=\"" << centre[0] << "\" cy=\"" << centre[1] << "\" r=\""
-        << r << "\" ";
+  m_out << "<circle ";
+  m_out << m_att("cx", centre[0]) << m_att("cy", centre[1]) << m_att("r", r);
 
   // Styling
   m_out << m_fill_color << ' ' << m_line_color << ' ' << m_linewidth;
@@ -133,7 +135,6 @@ void BackendSVG::circle_begin(const vfloat2_t &centre, const float r) noexcept {
 
 void BackendSVG::circle_end() noexcept { m_out << "</circle>\n"; }
 
-
 void BackendSVG::circle(const vfloat2_t &centre, float r) noexcept {
   circle_begin(centre, r);
   circle_end();

src/backend/BackendSVG.hpp

@@ -40,10 +40,34 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include "util/Exception.hpp"
 #include "util/Vector.hpp"
 
+#include <iomanip>
 #include <ostream>
+#include <sstream>
 
 namespace trase {
 
+/// Helper class for BackendSVG to format attributes as 'name="val" '
+class AttributeFormatter {
+  std::stringstream m_ss;
+  int m_precision = 4;
+
+public:
+  AttributeFormatter() { m_ss << std::setprecision(m_precision); }
+
+  /// Format as 'name="val" ' (inc quotes and space), and return a string
+  ///
+  /// @tparam T type of val
+  /// @param name name of attribute
+  /// @param val value of attribute
+  /// @return string of 'name="val" '
+  template <typename T>
+  std::string operator()(const std::string &name, const T val) {
+    m_ss.str("");
+    m_ss << name << "=\"" << val << "\" ";
+    return m_ss.str();
+  }
+};
+
 class BackendSVG {
   std::ostream &m_out;
   std::string m_linewidth;
@@ -67,6 +91,7 @@ class BackendSVG {
   std::string m_font_size_base;
   std::string m_font_face_base;
   TransformMatrix m_transform;
+  AttributeFormatter m_att;
 
   /// Add the opening circle tag to m_out
   /// @param centre coordinates of the centre of the circle