Example showing scale-invariant angle arc

daniel-s-ingram · QuLogic · commit 518b662b8d84 · 2020-09-10T23:39:33.000-04:00
diff --git a/examples/lines_bars_and_markers/angle_arc.py b/examples/lines_bars_and_markers/angle_arc.py
@@ -0,0 +1,92 @@
+"""
+==============
+Angle Arc Demo
+==============
+
+Draw an angle arc between two vectors
+"""
+from math import atan2, sqrt, pi
+import matplotlib.pyplot as plt
+import matplotlib.patches as mpatches
+
+fig, ax = plt.subplots()
+
+vec1 = ax.arrow(0, 0, 2, 1, head_width=0.05)
+vec2 = ax.arrow(0, 0, -1, 2, head_width=0.05)
+
+
+def get_vector_angle(vec):
+    """
+    Finds the angle of a FancyArrow. Probably
+    a better way to do this.
+
+    Parameters
+    ----------
+    vec : matplotlib.patches.FancyArrow
+
+    Returns
+    -------
+    float
+        Angle in radians between +x axis
+        and vec.
+    """
+    xy = vec.get_xy()
+    dx = max(xy[:, 0], key=abs) - min(xy[:, 0], key=abs)
+    dy = max(xy[:, 1], key=abs) - min(xy[:, 1], key=abs)
+    return atan2(dy, dx)*180/pi
+
+
+def draw_arc_between_vectors(ax, vec1, vec2):
+    """
+    Draws a scale-invariant arc between two vectors.
+
+    Arc will be drawn counterclockwise if the angle
+    of vec1 is smaller than the angle of vec2 and
+    will be drawn clockwise otherwise. Arc will be
+    drawn as a mpatches.Arc on the provided axes.
+
+    Parameters
+    ----------
+    ax : matplotlib.axes._subplots.AxesSubplot
+        The axes on which vec1 and vec2 are drawn
+    vec1 : matplotlib.patches.FancyArrow
+        Vector 1
+    vec2 : matplotlib.patches.FancyArrow
+        Vector 2
+    """
+    x0, y0 = ax.transData.transform((0, 0))
+    x1, y1 = ax.transData.transform((1, 1))
+    dx = x1 - x0
+    dy = y1 - y0
+    d = sqrt(dx**2 + dy**2)
+    width = d/dx
+    height = d/dy
+    norm = sqrt(width**2 + height**2)
+    width /= norm
+    height /= norm
+    theta1 = get_vector_angle(vec1)
+    theta2 = get_vector_angle(vec2)
+    arc = mpatches.Arc((0, 0), width, height, theta1=theta1, theta2=theta2)
+    try:
+        ax.patches[0].remove()
+    except:
+        pass
+    ax.add_patch(arc)
+    print(ax.patches[0].gid)
+
+
+def fig_resize(event):
+    draw_arc_between_vectors(ax, vec1, vec2)
+
+
+def axes_resize(ax):
+    draw_arc_between_vectors(ax, vec1, vec2)
+
+fig.canvas.mpl_connect("resize_event", fig_resize)
+ax.callbacks.connect("xlim_changed", axes_resize)
+ax.callbacks.connect("ylim_changed", axes_resize)
+
+plt.xlim(-3, 3)
+plt.ylim(-3, 3)
+
+plt.show()
