fixed a line collection rounding bug in agg that caused strange bugs when path lengths were 0

jdh2358 · jdh2358 · commit e82b391589d9 · 2007-06-12T16:17:01.000Z
svn path=/trunk/matplotlib/; revision=3387
diff --git a/lib/matplotlib/axes.py b/lib/matplotlib/axes.py
@@ -2417,6 +2417,7 @@ def vlines(self, x, ymin, ymax, colors='k', linestyle='solid',
 
         verts = [ ((thisx, thisymin), (thisx, thisymax))
                                     for thisx, (thisymin, thisymax) in zip(x,Y)]
+        #print 'creating line collection'
         coll = LineCollection(verts, colors=colors,
                               linestyle=linestyle, label=label)
         self.add_collection(coll)
diff --git a/lib/matplotlib/collections.py b/lib/matplotlib/collections.py
@@ -694,6 +694,7 @@ def draw(self, renderer):
                 offsets = zip(xs, ys)
 
         self.update_scalarmappable()
+        #print 'calling renderer draw line collection'
         renderer.draw_line_collection(
             segments, transform, self.clipbox,
             self._colors, self._lw, self._ls, self._aa, offsets,
diff --git a/lib/matplotlib/mpl-data/matplotlibrc b/lib/matplotlib/mpl-data/matplotlibrc
@@ -28,7 +28,6 @@
 #     Agg Cairo GD GDK Paint PS PDF SVG Template
 backend      : TkAgg
 numerix      : numpy  # numpy, Numeric or numarray
-units        : True
 #interactive  : False      # see http://matplotlib.sourceforge.net/interactive.html
 #toolbar      : toolbar2   # None | classic | toolbar2
 #timezone     : UTC        # a pytz timezone string, eg US/Central or Europe/Paris
diff --git a/matplotlibrc.template b/matplotlibrc.template
@@ -28,7 +28,6 @@
 #     Agg Cairo GD GDK Paint PS PDF SVG Template
 backend      : %(backend)s
 numerix      : %(numerix)s  # numpy, Numeric or numarray
-units        : True
 #interactive  : False      # see http://matplotlib.sourceforge.net/interactive.html
 #toolbar      : toolbar2   # None | classic | toolbar2
 #timezone     : UTC        # a pytz timezone string, eg US/Central or Europe/Paris
diff --git a/src/_backend_agg.cpp b/src/_backend_agg.cpp
@@ -579,6 +579,53 @@ RendererAgg::draw_polygon(const Py::Tuple& args) {
   
 }
 
+
+
+SnapData
+SafeSnap::snap (const float& x, const float& y) {
+  xsnap = (int)x + 0.5;
+  ysnap = (int)y + 0.5;
+
+
+  
+  if ( first || ( (xsnap!=lastxsnap) || (ysnap!=lastysnap) ) ) {
+    lastxsnap = xsnap;
+    lastysnap = ysnap;
+    lastx = x;
+    lasty = y;
+    first = false;
+    return SnapData(true, xsnap, ysnap);
+  }
+
+  // ok both are equal and we need to do an offset
+  if ( (x==lastx) && (y==lasty) ) {
+    // no choice but to return equal coords; set newpoint = false
+    lastxsnap = xsnap;
+    lastysnap = ysnap;
+    lastx = x;
+    lasty = y;
+    return SnapData(false, xsnap, ysnap);    
+  }
+
+  // ok the real points are not identical but the rounded ones, so do
+  // a one pixel offset
+  if (x>lastx) xsnap += 1.;
+  else if (x<lastx) xsnap -= 1.;
+
+  if (y>lasty) ysnap += 1.;
+  else if (y<lasty) ysnap -= 1.;
+
+  lastxsnap = xsnap;
+  lastysnap = ysnap;
+  lastx = x;
+  lasty = y;
+  return SnapData(true, xsnap, ysnap);    
+}  
+		 
+		 
+      
+
+
 Py::Object
 RendererAgg::draw_line_collection(const Py::Tuple& args) {
   
@@ -669,8 +716,14 @@ RendererAgg::draw_line_collection(const Py::Tuple& args) {
     xys = segments[i%Nsegments];
     size_t numtups = xys.length();
     if (numtups<2) continue;
+    
+
     bool snapto=numtups==2;
     agg::path_storage path;
+
+    //std::cout << "trying snapto " << numtups << " " << snapto << std::endl;
+
+    SafeSnap snap;
     
     
     for (size_t j=0; j<numtups; j++) {
@@ -694,8 +747,17 @@ RendererAgg::draw_line_collection(const Py::Tuple& args) {
       }
       
       if (snapto) { // snap to pixel for len(2) lines
-	thisx = (int)thisx + 0.5;
-	thisy = (int)thisy + 0.5;
+	SnapData snapdata(snap.snap(thisx, thisy));
+	// TODO: process newpoint
+	//if (!snapdata.newpoint) {
+	//  std::cout << "newpoint warning " << thisx << " " << thisy << std::endl;
+	//}
+	//std::cout << "snapto" << thisx << " " << thisy << std::endl;
+	thisx = snapdata.xsnap;
+	thisy = snapdata.ysnap;
+
+	//thisx = (int)thisx + 0.5;
+	//thisy = (int)thisy + 0.5;
       }
       
       if (j==0)  path.move_to(thisx, height-thisy);
diff --git a/src/_backend_agg.h b/src/_backend_agg.h
@@ -54,6 +54,26 @@ typedef agg::amask_no_clip_gray8 alpha_mask_type;
 typedef agg::renderer_base<agg::pixfmt_gray8> renderer_base_alpha_mask_type;
 typedef agg::renderer_scanline_aa_solid<renderer_base_alpha_mask_type> renderer_alpha_mask_type;
 
+struct SnapData {
+  SnapData(const bool& newpoint, const float& xsnap, const float& ysnap) :
+    newpoint(newpoint), xsnap(xsnap), ysnap(ysnap) {}
+  bool newpoint;
+  float xsnap, ysnap;
+};
+
+class SafeSnap {
+  // snap to pixel center, avoiding 0 path length rounding errors.
+public:
+  SafeSnap() : first(true), xsnap(0.0), lastx(0.0), lastxsnap(0.0),
+	       ysnap(0.0), lasty(0.0), lastysnap(0.0)  {}
+  SnapData snap (const float& x, const float& y);
+      
+private:
+  bool first;
+  float xsnap, lastx, lastxsnap, ysnap, lasty, lastysnap;
+};
+
+
 // a helper class to pass agg::buffer objects around.  agg::buffer is
 // a class in the swig wrapper
 class BufferRegion : public Py::PythonExtension<BufferRegion> {
