[GUI] Support gui.arrow() and gui.arrows()

docs/gui.rst

@@ -10,10 +10,10 @@ Create a window
 ---------------
 
 
-.. function:: ti.GUI(title, res, bgcolor = 0x000000)
+.. function:: ti.GUI(title = 'Taichi', res = (512, 512), bgcolor = 0x000000)
 
-    :parameter title: (string) the window title
-    :parameter res: (scalar or tuple) resolution / size of the window
+    :parameter title: (optional, string) the window title
+    :parameter res: (optional, scalar or tuple) resolution / size of the window
     :parameter bgcolor: (optional, RGB hex) background color of the window
     :return: (GUI) an object represents the window
 

python/taichi/misc/gui.py

@@ -34,7 +34,7 @@ class Event:
     PRESS = ti_core.KeyEvent.EType.Press
     RELEASE = ti_core.KeyEvent.EType.Release
 
-    def __init__(self, name, res=512, background_color=0x0):
+    def __init__(self, name='Taichi', res=512, background_color=0x0):
         self.name = name
         if isinstance(res, numbers.Number):
             res = (res, res)
@@ -286,6 +286,30 @@ def line(self, begin, end, radius=1, color=0xFFFFFF):
         self.canvas.path_single(begin[0], begin[1], end[0], end[1], color,
                                 radius)
 
+    @staticmethod
+    def _arrow_to_lines(orig, major, tip_scale=0.2, angle=45):
+        import math
+        angle = math.radians(180 - angle)
+        c, s = math.cos(angle), math.sin(angle)
+        minor1 = np.array([major[:, 0] * c - major[:, 1] * s,
+                           major[:, 0] * s + major[:, 1] * c]).swapaxes(0, 1)
+        minor2 = np.array([major[:, 0] * c + major[:, 1] * s,
+                          -major[:, 0] * s + major[:, 1] * c]).swapaxes(0, 1)
+        end = orig + major
+        return [(orig, end),
+                (end, end + minor1 * tip_scale),
+                (end, end + minor2 * tip_scale)]
+
+    def arrows(self, orig, dir, radius=1, color=0xffffff, **kwargs):
+        for begin, end in self._arrow_to_lines(orig, dir, **kwargs):
+            self.lines(begin, end, radius, color)
+
+    def arrow(self, orig, dir, radius=1, color=0xffffff, **kwargs):
+        orig = np.array([orig])
+        dir = np.array([dir])
+        for begin, end in self._arrow_to_lines(orig, dir, **kwargs):
+            self.line(begin[0], end[0], radius, color)
+
     def rect(self, topleft, bottomright, radius=1, color=0xFFFFFF):
         a = topleft[0], topleft[1]
         b = bottomright[0], topleft[1]

python/taichi/misc/image.py

@@ -71,7 +71,7 @@ def imread(filename, channels=0):
     return img.swapaxes(0, 1)[:, ::-1, :]
 
 
-def imshow(img, window_name='Taichi'):
+def imshow(img, window_name='imshow'):
     """
     Show image in a Taichi GUI.
     """