grapher: scale from right end of graph

The right side of the graph represents the most recent time. Since
there is never anything interesting to the right of that, it makes
sense to have the origin of the scaling be there.

* grapher/Graph.hxx (getHorizontalScale): new function
* grapher/GraphStyle.cxx (GraphStyleBar::draw, GraphStyleDot::draw,
  GraphStyleEvent::draw): Use cairo transform functions to set up
  scaling.
  (GraphStyleBar::dataIndexAtPoint, GraphStyleEvent::dataIndexAtPoint):
  Base calculations on scaling from right.

3 files changed, 54 insertions, 28 deletions

diff --git a/grapher/Graph.cxx b/grapher/Graph.cxx
index afb52c74..4d697ae6 100644
--- a/grapher/Graph.cxx
+++ b/grapher/Graph.cxx
@@ -47,8 +47,7 @@ void Graph::draw(Cairo::RefPtr<Cairo::Context> cr)
       _left = _right - 5000;
     }
   cr->save();
-  double horizScale
-    = _zoomFactor * _graphWidth / static_cast<double>(_right - _left);
+  double horizScale = getHorizontalScale();
   cr->translate(_xOffset, _yOffset);
   cr->set_line_width(_lineWidth);
 
@@ -103,10 +102,11 @@ void Graph::draw(Cairo::RefPtr<Cairo::Context> cr)
   cr->select_font_face("Sans", Cairo::FONT_SLANT_NORMAL,
                        Cairo::FONT_WEIGHT_NORMAL);
   cr->set_font_size(10.0);
-  cr->move_to(_xOffset, _yOffset);
-  cr->line_to(_xOffset, _height);
-  cr->move_to(_xOffset, _graphHeight);
-  cr->line_to(_graphWidth, _graphHeight);
+  cr->translate(_xOffset, 0.0);
+  cr->move_to(0.0, _yOffset);
+  cr->line_to(0.0, _height);
+  cr->move_to(0.0, _graphHeight);
+  cr->line_to(_graphWidth - _xOffset, _graphHeight);
   cr->stroke();
   std::valarray<double> dash(1);
   dash[0] = _graphHeight / 10;
@@ -114,7 +114,7 @@ void Graph::draw(Cairo::RefPtr<Cairo::Context> cr)
   double prevTextAdvance = 0;
   for (int64_t tickVal = startTime; tickVal <= _right; tickVal += majorUnit)
     {
-      double x = (tickVal - _left) * horizScale + _xOffset;
+      double x = (tickVal - _right) * horizScale + _graphWidth;
       cr->move_to(x, _yOffset);
       cr->line_to(x, _graphHeight);
       std::ostringstream stream;
@@ -170,8 +170,7 @@ bool Graph::containsPoint(double x, double y)
 
 int64_t Graph::getTimeAtPoint(double x)
 {
-  return (_left
-          + (_right - _left) * ((x - _xOffset)/(_zoomFactor * _graphWidth)));
+  return (x - _graphWidth) / getHorizontalScale() + _right;
 }
 
 void Graph::window2GraphCoords(double x, double y,
diff --git a/grapher/Graph.hxx b/grapher/Graph.hxx
index d9f615b3..0853d988 100644
--- a/grapher/Graph.hxx
+++ b/grapher/Graph.hxx
@@ -51,6 +51,14 @@ public:
   int64_t getTimeAtPoint(double x);
   void window2GraphCoords(double x, double y, double& xgraph, double& ygraph);
   static void setCurrentTime(int64_t time) { _currentTime = time; }
+
+  /*
+   * universal horizontal factor
+   */
+  double getHorizontalScale()
+  {
+    return _zoomFactor * _graphWidth / static_cast<double>(_right - _left);
+  }
 protected:
   GraphDataList _datasets;
   int64_t _left;
diff --git a/grapher/GraphStyle.cxx b/grapher/GraphStyle.cxx
index 5a6621bd..86cb823c 100644
--- a/grapher/GraphStyle.cxx
+++ b/grapher/GraphStyle.cxx
@@ -31,8 +31,15 @@ void GraphStyleBar::draw(std::tr1::shared_ptr<GraphDataBase> graphData,
   int64_t left, right;
   double top, bottom;
   graph->getExtents(left, right, top, bottom);
-  double horizScale = (graph->_zoomFactor * graph->_graphWidth
-                       / static_cast<double>(right - left));
+  double horizScale = graph->getHorizontalScale();
+  cr->save();
+  double lineWidth = cr->get_line_width();
+  cr->translate(graph->_graphWidth, 0.0);
+  cr->scale(horizScale, 1.0);
+  cr->translate(left - right, 0.0);
+  cr->set_line_width(lineWidth / horizScale);
+  cr->set_source_rgba(graphData->color[0], graphData->color[1],
+                      graphData->color[2], 1.0);
   GraphDataBase::TimeList::iterator lower
     = lower_bound(graphData->times.begin(), graphData->times.end(), left);
   GraphDataBase::TimeList::iterator upper
@@ -42,14 +49,13 @@ void GraphStyleBar::draw(std::tr1::shared_ptr<GraphDataBase> graphData,
        ++ditr)
     {
       size_t dataIndex = ditr - graphData->times.begin();
-      cr->set_source_rgba(graphData->color[0], graphData->color[1],
-                          graphData->color[2], 1.0);
-      cr->move_to((*ditr - left) * horizScale, 0);
-      cr->line_to((*ditr - left) * horizScale,
+      cr->move_to((*ditr - left), 0);
+      cr->line_to((*ditr - left),
                   realData->data[dataIndex] * graph->_graphHeight
                   / graphData->scale);
       cr->stroke();
     }
+  cr->restore();
 }
 
 ssize_t GraphStyleBar::dataIndexAtPoint(double x, double y,
@@ -63,7 +69,7 @@ ssize_t GraphStyleBar::dataIndexAtPoint(double x, double y,
   int64_t left, right;
   double top, bottom;
   graph->getExtents(left, right, top, bottom);
-  double t = graph->getTimeAtPoint(x);
+  int64_t t = graph->getTimeAtPoint(x);
   TimeListPair range
     = equal_range(graphData->times.begin(), graphData->times.end(), t);
   if (range.first == graphData->times.end())
@@ -89,12 +95,14 @@ void GraphStyleDot::draw(std::tr1::shared_ptr<GraphDataBase> graphData,
   int64_t left, right;
   double top, bottom;
   graph->getExtents(left, right, top, bottom);
-  double horizScale = (graph->_zoomFactor * graph->_graphWidth
-                       / static_cast<double>(right - left));
+  double horizScale = graph->getHorizontalScale();;
   GraphDataBase::TimeList::iterator lower
     = lower_bound(graphData->times.begin(), graphData->times.end(), left);
   GraphDataBase::TimeList::iterator upper
     = upper_bound(graphData->times.begin(), graphData->times.end(), right);
+  cr->translate(graph->_graphWidth, 0.0);
+  cr->scale(horizScale, 1.0);
+  cr->translate(left - right, 0.0);
   cr->set_source_rgba(graphData->color[0], graphData->color[1],
                       graphData->color[2], 1.0);
 
@@ -103,12 +111,14 @@ void GraphStyleDot::draw(std::tr1::shared_ptr<GraphDataBase> graphData,
        ++ditr)
     {
       size_t dataIndex = ditr - graphData->times.begin();
-      cr->arc((*ditr - left) * horizScale,
+      // XXX Fix unequal scale in x, y
+      cr->arc((*ditr - left),
               (realData->data[dataIndex]
                * graph->_graphHeight / graphData->scale),
-              graph->_lineWidth / 2.0, 0.0, M_PI * 2.0);
+              (graph->_lineWidth / (2.0 * horizScale)), 0.0, M_PI * 2.0);
       cr->fill();
     }
+  cr->restore();
 }
 
 GraphStyleEvent GraphStyleEvent::instance;
@@ -123,8 +133,7 @@ void GraphStyleEvent::draw(std::tr1::shared_ptr<GraphDataBase> graphData,
   int64_t left, right;
   double top, bottom;
   graph->getExtents(left, right, top, bottom);
-  double horizScale = (graph->_zoomFactor * graph->_graphWidth
-                       / static_cast<double>(right - left));
+  double horizScale = graph->getHorizontalScale();
   double eventHeight = graph->_graphHeight * (graphData->scale / 100.0);
   cr->save();
   cr->set_line_width(3 * graph->_lineWidth);
@@ -134,6 +143,12 @@ void GraphStyleEvent::draw(std::tr1::shared_ptr<GraphDataBase> graphData,
   cr->line_to(graph->_graphWidth, eventHeight);
   cr->stroke();
   cr->restore();
+  cr->save();
+  // Global translation for user scaling
+  cr->translate(graph->_graphWidth, 0.0);
+  cr->scale(horizScale, 1.0);
+  cr->translate(left - right, 0.0);
+
   GraphDataBase::TimeList::iterator lower
     = lower_bound(graphData->times.begin(), graphData->times.end(), left);
   GraphDataBase::TimeList::iterator upper
@@ -147,12 +162,15 @@ void GraphStyleEvent::draw(std::tr1::shared_ptr<GraphDataBase> graphData,
       cr->save();
       cr->set_source_rgba(graphData->color[0], graphData->color[1],
                           graphData->color[2], 1.0);
-      cr->rectangle((*ditr - left) * horizScale - 1.5 * graph->_lineWidth,
+      // Do cairo transformations here instead of our own math?
+      cr->rectangle((*ditr - left) - (1.5 * graph->_lineWidth / horizScale),
                     eventHeight - 1.5 * graph->_lineWidth,
-                    3.0 * graph->_lineWidth, 3.0 * graph->_lineWidth);
+                    3.0 * (graph->_lineWidth / horizScale),
+                    3.0 * graph->_lineWidth);
       cr->fill();
       cr->restore();
     }
+  cr->restore();
 }
 
 ssize_t GraphStyleEvent::dataIndexAtPoint(double x, double y,
@@ -166,8 +184,7 @@ ssize_t GraphStyleEvent::dataIndexAtPoint(double x, double y,
   int64_t left, right;
   double top, bottom;
   graph->getExtents(left, right, top, bottom);
-  double horizScale = (graph->_zoomFactor * graph->_graphWidth
-                       / static_cast<double>(right - left));
+  double horizScale = graph->getHorizontalScale();
   double eventHeight = graph->_graphHeight * (graphData->scale / 100.0);
   GraphDataBase::TimeList::iterator lower
     = lower_bound(graphData->times.begin(), graphData->times.end(), left);
@@ -177,12 +194,14 @@ ssize_t GraphStyleEvent::dataIndexAtPoint(double x, double y,
   double xgraph, ygraph;
   graph->window2GraphCoords(x, y, xgraph, ygraph);
   double yrect = eventHeight - 1.5 * graph->_lineWidth;
+  double rectWidth = 3 * graph->_lineWidth;
   for (GraphDataBase::TimeList::iterator ditr = lower, de = upper;
        ditr != de;
        ++ditr)
     {
-      double xrect = (*ditr - left) * horizScale - 1.5 * graph->_lineWidth;
-      if (xrect <= xgraph && xgraph < xrect + 3.0 * graph->_lineWidth
+      double xrect = ((*ditr - right) * horizScale + graph->_graphWidth
+                      - .5 * rectWidth);
+      if (xrect <= xgraph && xgraph < xrect + rectWidth
           && yrect <= ygraph && ygraph < yrect + 3.0 * graph->_lineWidth)
         return static_cast<ssize_t>(distance(graphData->times.begin(), ditr));
     }