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gbrault
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jupytersketcher
зеркало из https://github.com/gbrault/jupytersketcher.git
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update

Hans Petter Langtangen 13 лет назад
Родитель
efb19681ca
Сommit
70eac6e121
6 измененных файлов с 515 добавлено и 5 удалено
Единый вид Показать статистику Diff
  1. BIN
      doc/src/sketcher/figs-sketcher/vehicle0.png
  2. BIN
      doc/src/sketcher/figs-sketcher/vehicle0v2.png
  3. 69 4
      doc/src/sketcher/sketcher.do.txt
  4. 207 0
      doc/src/sketcher/src-sketcher/vehicle0_animation/anim.html
  5. 207 0
      doc/src/sketcher/src-sketcher/vehicle1_animation/anim.html
  6. 32 1
      pysketcher/shapes.py

BIN
doc/src/sketcher/figs-sketcher/vehicle0.png
Просмотреть файл


BIN
doc/src/sketcher/figs-sketcher/vehicle0v2.png
Просмотреть файл


+ 69 - 4
doc/src/sketcher/sketcher.do.txt
Просмотреть файл 

@@ -229,7 +229,7 @@ FIGURE: [figs-sketcher/vehicle0v2.png, width=400] Changed properties of parts of
 
 We can also change position of parts of the figure and thereby make
 
 We can also change position of parts of the figure and thereby make
 
 animations, as shown next.
 
 animations, as shown next.
 
 
 
-=== Animation ===
 
+=== Animation: Translating the Vehicle ===
 
 
 
 Can we make our little vehicle roll? A first attempt will be to
 
 Can we make our little vehicle roll? A first attempt will be to
 
 fake rolling by just displacing all parts of the vehicle.
 
 fake rolling by just displacing all parts of the vehicle.
 
@@ -301,11 +301,76 @@ movie(files, encoder='html', output_file='anim')
 
 !ec
 
 !ec
 
 This command makes a movie that is actually an HTML file `anim.html`,
 
 This command makes a movie that is actually an HTML file `anim.html`,
 
 which can be loaded into a web browser.
 
 which can be loaded into a web browser.
 
-You can try this by running the present example in
 
+You can try this by running the present example in the file
 
 # #ifdef PRIMER_BOOK
 
 # #ifdef PRIMER_BOOK
 
-the file `vehicle0.py`.
 
+`vehicle0.py`.
 
 # #else
 
 # #else
 
-the file "vehicle0.py":
 
+"`vehicle0.py`": "http://hplgit.github.com/pysketcher/doc/src/sketcher/sketcher.do.txt".
 
+# #endif
 
+
 
+=== Animation: Rolling the Wheels ===
 
+
 
+It is time to show rolling wheels. To this end, we make somewhat
 
+more complicated wheels with spokes as on a bicyle, formed by
 
+two crossing lines, see Figure ref{sketcher:fig:vehicle1}.
 
+The construction of the wheels will now involve a circle
 
+and two lines:
 
+!bc pycod
 
+R = 1.  # radius of wheel
 
+wheel1 = Compose({'wheel':
 
+                  Circle(center=(4, R), radius=R),
 
+                  'cross':
 
+                  Compose({'cross1': Line((4,0), (4,2*R)),
 
+                          'cross2': Line((4-R,R), (4+R,R))})})
 
+wheel2 = wheel1.copy()
 
+wheel2.translate((4,0))
 
+!ec
 
+Observe that `wheel1.copy()` copies all the objects that make
 
+up the first wheel, and `wheel2.translate` translates all
 
+the copied objects.
 
+
 
+FIGURE: [figs-sketcher/vehicle1.png, width=400] Wheels with spokes to show rotation. label{sketcher:fig:vehicle1}
 
+
 
+The `move_vehicle` function need to displace all the objects in the
 
+entire vehicle and also rotate the crosses in the wheels.
 
+The rotation angle follows from the fact that the arc length
 
+of a rolling wheel equals the displacement of the center of
 
+the wheel, leading to a rotation angle
 
+!bc pycod
 
+angle = - displacement[0]/R
 
+!ec
 
+With `wheel1_center` tracking the $x$ coordinate of the center
 
+of the front wheel, we can rotate that wheel by
 
+!bc pycod
 
+w1 = fig['vehicle']['wheels']['wheel1']
 
+from math import degrees
 
+w1.rotate(degrees(angle), center=(wheel1_center, R))
 
+!ec
 
+The `rotate` function takes two parameters: the rotation angle
 
+(in degrees) and the center point of the rotation, which is the
 
+center of the wheel in this case. The other wheel is rotated by
 
+!bc pycod
 
+w2 = fig['vehicle']['wheels']['wheel2']
 
+w2.rotate(degrees(angle), center=(wheel1_center+4, R))
 
+!ec
 
+That is, the angle is the same, but the rotation point is different.
 
+The update of the center point is done by `wheel1_center += displacement[0]`.
 
+The complete `move_vehicle` function then becomes
 
+!bc pycod
 
+wheel1_center = 7   # start position
 
+
 
+def move_vehicle(t, fig):
 
+    displacement = dt*v(t)
 
+    fig['vehicle'].translate(displacement)
 
+    global wheel1_center
 
+    wheel1_center += displacement[0]
 
+    angle = - displacement[0]/R
 
+    w1 = fig['vehicle']['wheels']['wheel1']
 
+    w1.rotate(degrees(angle), center=(wheel1_center, R))
 
+    w2 = fig['vehicle']['wheels']['wheel2']
 
+    w2.rotate(degrees(angle), center=(wheel1_center+4, R))
 
+!ec
 
+
 
 
 
 
 
 The great advantage with making figures this way through programming,
 
 The great advantage with making figures this way through programming,

+ 207 - 0
doc/src/sketcher/src-sketcher/vehicle0_animation/anim.html
Просмотреть файл 

@@ -0,0 +1,207 @@
 
+<html>
 
+<head>
 
+</head>
 
+<body>
 
+
 
+<script language="Javascript">
 
+<!---
 
+var num_images_anim = 35;
 
+var img_width = 800;
 
+var img_height = 600;
 
+var interval = 40;    
+var images_anim = new Array();
 
+
 
+function preload_images_anim()
 
+{
 
+   t = document.getElementById("progress");
 
+
 
+   t.innerHTML = "Preloading image ";
 
+   images_anim[0] = new Image(img_width, img_height);
 
+   images_anim[0].src = "tmp_frame_0000.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[1] = new Image(img_width, img_height);
 
+   images_anim[1].src = "tmp_frame_0001.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[2] = new Image(img_width, img_height);
 
+   images_anim[2].src = "tmp_frame_0002.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[3] = new Image(img_width, img_height);
 
+   images_anim[3].src = "tmp_frame_0003.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[4] = new Image(img_width, img_height);
 
+   images_anim[4].src = "tmp_frame_0004.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[5] = new Image(img_width, img_height);
 
+   images_anim[5].src = "tmp_frame_0005.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[6] = new Image(img_width, img_height);
 
+   images_anim[6].src = "tmp_frame_0006.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[7] = new Image(img_width, img_height);
 
+   images_anim[7].src = "tmp_frame_0007.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[8] = new Image(img_width, img_height);
 
+   images_anim[8].src = "tmp_frame_0008.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[9] = new Image(img_width, img_height);
 
+   images_anim[9].src = "tmp_frame_0009.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[10] = new Image(img_width, img_height);
 
+   images_anim[10].src = "tmp_frame_0010.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[11] = new Image(img_width, img_height);
 
+   images_anim[11].src = "tmp_frame_0011.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[12] = new Image(img_width, img_height);
 
+   images_anim[12].src = "tmp_frame_0012.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[13] = new Image(img_width, img_height);
 
+   images_anim[13].src = "tmp_frame_0013.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[14] = new Image(img_width, img_height);
 
+   images_anim[14].src = "tmp_frame_0014.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[15] = new Image(img_width, img_height);
 
+   images_anim[15].src = "tmp_frame_0015.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[16] = new Image(img_width, img_height);
 
+   images_anim[16].src = "tmp_frame_0016.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[17] = new Image(img_width, img_height);
 
+   images_anim[17].src = "tmp_frame_0017.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[18] = new Image(img_width, img_height);
 
+   images_anim[18].src = "tmp_frame_0018.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[19] = new Image(img_width, img_height);
 
+   images_anim[19].src = "tmp_frame_0019.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[20] = new Image(img_width, img_height);
 
+   images_anim[20].src = "tmp_frame_0020.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[21] = new Image(img_width, img_height);
 
+   images_anim[21].src = "tmp_frame_0021.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[22] = new Image(img_width, img_height);
 
+   images_anim[22].src = "tmp_frame_0022.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[23] = new Image(img_width, img_height);
 
+   images_anim[23].src = "tmp_frame_0023.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[24] = new Image(img_width, img_height);
 
+   images_anim[24].src = "tmp_frame_0024.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[25] = new Image(img_width, img_height);
 
+   images_anim[25].src = "tmp_frame_0025.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[26] = new Image(img_width, img_height);
 
+   images_anim[26].src = "tmp_frame_0026.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[27] = new Image(img_width, img_height);
 
+   images_anim[27].src = "tmp_frame_0027.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[28] = new Image(img_width, img_height);
 
+   images_anim[28].src = "tmp_frame_0028.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[29] = new Image(img_width, img_height);
 
+   images_anim[29].src = "tmp_frame_0029.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[30] = new Image(img_width, img_height);
 
+   images_anim[30].src = "tmp_frame_0030.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[31] = new Image(img_width, img_height);
 
+   images_anim[31].src = "tmp_frame_0031.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[32] = new Image(img_width, img_height);
 
+   images_anim[32].src = "tmp_frame_0032.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[33] = new Image(img_width, img_height);
 
+   images_anim[33].src = "tmp_frame_0033.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[34] = new Image(img_width, img_height);
 
+   images_anim[34].src = "tmp_frame_0034.png";
 
+        
+   t.innerHTML = "";
 
+}
 
+
 
+function tick_anim()
 
+{
 
+   if (frame_anim > num_images_anim - 1)
 
+       frame_anim = 0;
 
+
 
+   document.movie.src = images_anim[frame_anim].src;
 
+   frame_anim += 1;
 
+   tt = setTimeout("tick_anim()", interval);
 
+}
 
+
 
+function startup_anim()
 
+{
 
+   preload_images_anim();
 
+   frame_anim = 0;
 
+   setTimeout("tick_anim()", interval);
 
+}
 
+
 
+function stopit()
 
+{ clearTimeout(tt); }
 
+
 
+function restart_anim()
 
+{ tt = setTimeout("tick_anim()", interval); }
 
+
 
+function slower()
 
+{ interval = interval/0.7; }
 
+
 
+function faster()
 
+{ interval = interval*0.7; }
 
+
 
+// --->
 
+</script>
 
+
 
+<form>
 
+&nbsp;
 
+<input type="button" value="Start movie" onClick="startup_anim()">
 
+<input type="button" value="Pause movie" onClick="stopit()">
 
+<input type="button" value="Restart movie" onClick="restart_anim()">
 
+&nbsp;
 
+<input type="button" value="Slower" onClick="slower()">
 
+<input type="button" value="Faster" onClick="faster()">
 
+</form>
 
+
 
+<p><div ID="progress"></div></p>
 
+<img src="tmp_frame_0000.png" name="movie" border=2/>
 
+
 
+</body>
 
+</html>

+ 207 - 0
doc/src/sketcher/src-sketcher/vehicle1_animation/anim.html
Просмотреть файл 

@@ -0,0 +1,207 @@
 
+<html>
 
+<head>
 
+</head>
 
+<body>
 
+
 
+<script language="Javascript">
 
+<!---
 
+var num_images_anim = 35;
 
+var img_width = 800;
 
+var img_height = 600;
 
+var interval = 40;    
+var images_anim = new Array();
 
+
 
+function preload_images_anim()
 
+{
 
+   t = document.getElementById("progress");
 
+
 
+   t.innerHTML = "Preloading image ";
 
+   images_anim[0] = new Image(img_width, img_height);
 
+   images_anim[0].src = "tmp_frame_0000.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[1] = new Image(img_width, img_height);
 
+   images_anim[1].src = "tmp_frame_0001.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[2] = new Image(img_width, img_height);
 
+   images_anim[2].src = "tmp_frame_0002.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[3] = new Image(img_width, img_height);
 
+   images_anim[3].src = "tmp_frame_0003.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[4] = new Image(img_width, img_height);
 
+   images_anim[4].src = "tmp_frame_0004.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[5] = new Image(img_width, img_height);
 
+   images_anim[5].src = "tmp_frame_0005.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[6] = new Image(img_width, img_height);
 
+   images_anim[6].src = "tmp_frame_0006.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[7] = new Image(img_width, img_height);
 
+   images_anim[7].src = "tmp_frame_0007.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[8] = new Image(img_width, img_height);
 
+   images_anim[8].src = "tmp_frame_0008.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[9] = new Image(img_width, img_height);
 
+   images_anim[9].src = "tmp_frame_0009.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[10] = new Image(img_width, img_height);
 
+   images_anim[10].src = "tmp_frame_0010.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[11] = new Image(img_width, img_height);
 
+   images_anim[11].src = "tmp_frame_0011.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[12] = new Image(img_width, img_height);
 
+   images_anim[12].src = "tmp_frame_0012.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[13] = new Image(img_width, img_height);
 
+   images_anim[13].src = "tmp_frame_0013.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[14] = new Image(img_width, img_height);
 
+   images_anim[14].src = "tmp_frame_0014.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[15] = new Image(img_width, img_height);
 
+   images_anim[15].src = "tmp_frame_0015.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[16] = new Image(img_width, img_height);
 
+   images_anim[16].src = "tmp_frame_0016.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[17] = new Image(img_width, img_height);
 
+   images_anim[17].src = "tmp_frame_0017.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[18] = new Image(img_width, img_height);
 
+   images_anim[18].src = "tmp_frame_0018.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[19] = new Image(img_width, img_height);
 
+   images_anim[19].src = "tmp_frame_0019.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[20] = new Image(img_width, img_height);
 
+   images_anim[20].src = "tmp_frame_0020.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[21] = new Image(img_width, img_height);
 
+   images_anim[21].src = "tmp_frame_0021.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[22] = new Image(img_width, img_height);
 
+   images_anim[22].src = "tmp_frame_0022.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[23] = new Image(img_width, img_height);
 
+   images_anim[23].src = "tmp_frame_0023.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[24] = new Image(img_width, img_height);
 
+   images_anim[24].src = "tmp_frame_0024.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[25] = new Image(img_width, img_height);
 
+   images_anim[25].src = "tmp_frame_0025.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[26] = new Image(img_width, img_height);
 
+   images_anim[26].src = "tmp_frame_0026.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[27] = new Image(img_width, img_height);
 
+   images_anim[27].src = "tmp_frame_0027.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[28] = new Image(img_width, img_height);
 
+   images_anim[28].src = "tmp_frame_0028.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[29] = new Image(img_width, img_height);
 
+   images_anim[29].src = "tmp_frame_0029.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[30] = new Image(img_width, img_height);
 
+   images_anim[30].src = "tmp_frame_0030.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[31] = new Image(img_width, img_height);
 
+   images_anim[31].src = "tmp_frame_0031.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[32] = new Image(img_width, img_height);
 
+   images_anim[32].src = "tmp_frame_0032.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[33] = new Image(img_width, img_height);
 
+   images_anim[33].src = "tmp_frame_0033.png";
 
+        
+   t.innerHTML = "Preloading image ";
 
+   images_anim[34] = new Image(img_width, img_height);
 
+   images_anim[34].src = "tmp_frame_0034.png";
 
+        
+   t.innerHTML = "";
 
+}
 
+
 
+function tick_anim()
 
+{
 
+   if (frame_anim > num_images_anim - 1)
 
+       frame_anim = 0;
 
+
 
+   document.movie.src = images_anim[frame_anim].src;
 
+   frame_anim += 1;
 
+   tt = setTimeout("tick_anim()", interval);
 
+}
 
+
 
+function startup_anim()
 
+{
 
+   preload_images_anim();
 
+   frame_anim = 0;
 
+   setTimeout("tick_anim()", interval);
 
+}
 
+
 
+function stopit()
 
+{ clearTimeout(tt); }
 
+
 
+function restart_anim()
 
+{ tt = setTimeout("tick_anim()", interval); }
 
+
 
+function slower()
 
+{ interval = interval/0.7; }
 
+
 
+function faster()
 
+{ interval = interval*0.7; }
 
+
 
+// --->
 
+</script>
 
+
 
+<form>
 
+&nbsp;
 
+<input type="button" value="Start movie" onClick="startup_anim()">
 
+<input type="button" value="Pause movie" onClick="stopit()">
 
+<input type="button" value="Restart movie" onClick="restart_anim()">
 
+&nbsp;
 
+<input type="button" value="Slower" onClick="slower()">
 
+<input type="button" value="Faster" onClick="faster()">
 
+</form>
 
+
 
+<p><div ID="progress"></div></p>
 
+<img src="tmp_frame_0000.png" name="movie" border=2/>
 
+
 
+</body>
 
+</html>

+ 32 - 1
pysketcher/shapes.py
Просмотреть файл 

@@ -81,9 +81,14 @@ class Shape:
 
                 return self.shapes[name]
 
                 return self.shapes[name]
 
             else:
 
             else:
 
                 for shape in self.shapes:
 
                 for shape in self.shapes:
 
+                    if isinstance(self.shapes[shape], (Curve,Point)):
 
+                        # Indexing of Curve/Point/Text is not possible
 
+                        raise TypeError(
 
+                            'Index "%s" is illegal' % name)
 
                     return self.shapes[shape][name]
 
                     return self.shapes[shape][name]
 
         else:
 
         else:
 
-            return self
 
+            raise Exception('This is a bug')
 
+
 
 
 
     def for_all_shapes(self, func, *args, **kwargs):
 
     def for_all_shapes(self, func, *args, **kwargs):
 
         if not hasattr(self, 'shapes'):
 
         if not hasattr(self, 'shapes'):
 
@@ -146,6 +151,9 @@ class Shape:
 
 
 
     def show_hierarchy(self, indent=0, format='std'):
 
     def show_hierarchy(self, indent=0, format='std'):
 
         """Recursive pretty print of hierarchy of objects."""
 
         """Recursive pretty print of hierarchy of objects."""
 
+        if not isinstance(self.shapes, dict):
 
+            print 'cannot print hierarchy when %s.shapes is not a dict' % \
 
+                  self.__class__.__name__
 
         s = ''
 
         s = ''
 
         if format == 'dict':
 
         if format == 'dict':
 
             s += '{'
 
             s += '{'
 
@@ -405,6 +413,29 @@ class Line(Shape):
 
             self.c = None
 
             self.c = None
 
             self.d = None
 
             self.d = None
 
 
 
+    def compute_formulas(self):
 
+        x, y = self.shapes['line'].x, self.shapes['line'].y
 
+
 
+        tol = 1E-14
 
+        # Define equations for line:
 
+        # y = a*x + b,  x = c*y + d
 
+        if abs(x[1] - x[0]) > tol:
 
+            self.a = (y[1] - y[0])/(x[1] - x[0])
 
+            self.b = y[0] - self.a*x[0]
 
+        else:
 
+            # Vertical line, y is not a function of x
 
+            self.a = None
 
+            self.b = None
 
+        if self.a is None:
 
+            self.c = 0
 
+        elif abs(self.a) > tol:
 
+            self.c = 1/float(self.a)
 
+            self.d = x[1]
 
+        else:  # self.a is 0
 
+            # Horizontal line, x is not a function of y
 
+            self.c = None
 
+            self.d = None
 
+
 
     def __call__(self, x=None, y=None):
 
     def __call__(self, x=None, y=None):
 
         """Given x, return y on the line, or given y, return x."""
 
         """Given x, return y on the line, or given y, return x."""
 
         self.compute_formulas()
 
         self.compute_formulas()