Hi, I just had to label a sequence of images with the position and scale of a moving object. To do this I took the nice example from http://matplotlib.sourceforge.net/users/event_handling.html (the one using blitting) and extended to be resizeable. The extension is trivial, but it might be useful to someone. The code is inlined at the end of this message.
Jorge # draggable rectangle with the animation blit techniques; see # http://www.scipy.org/Cookbook/Matplotlib/Animations import numpy as np import matplotlib.pyplot as plt class DraggableResizeableRectangle: """ Draggable and resizeable rectangle with the animation blit techniques. Based on example code at http://matplotlib.sourceforge.net/users/event_handling.html If *allow_resize* is *True* the recatngle can be resized by dragging its lines. *border_tol* specifies how close the pointer has to be to a line for the drag to be considered a resize operation. Dragging is still possible by clicking the interior of the rectangle. *fixed_aspect_ratio* determines if the recatngle keeps its aspect ratio during resize operations. """ lock = None # only one can be animated at a time def __init__(self, rect, border_tol=.15, allow_resize=True, fixed_aspect_ratio=True): self.rect = rect self.border_tol = border_tol self.allow_resize = allow_resize self.fixed_aspect_ratio = fixed_aspect_ratio self.press = None self.background = None def connect(self): 'connect to all the events we need' self.cidpress = self.rect.figure.canvas.mpl_connect( 'button_press_event', self.on_press) self.cidrelease = self.rect.figure.canvas.mpl_connect( 'button_release_event', self.on_release) self.cidmotion = self.rect.figure.canvas.mpl_connect( 'motion_notify_event', self.on_motion) def on_press(self, event): 'on button press we will see if the mouse is over us and store some data' if event.inaxes != self.rect.axes: return if DraggableRectangle.lock is not None: return contains, attrd = self.rect.contains(event) if not contains: return #print 'event contains', self.rect.xy x0, y0 = self.rect.xy w0, h0 = self.rect.get_width(), self.rect.get_height() aspect_ratio = np.true_divide(w0, h0) self.press = x0, y0, w0, h0, aspect_ratio, event.xdata, event.ydata DraggableRectangle.lock = self # draw everything but the selected rectangle and store the pixel buffer canvas = self.rect.figure.canvas axes = self.rect.axes self.rect.set_animated(True) canvas.draw() self.background = canvas.copy_from_bbox(self.rect.axes.bbox) # now redraw just the rectangle axes.draw_artist(self.rect) # and blit just the redrawn area canvas.blit(axes.bbox) def on_motion(self, event): 'on motion we will move the rect if the mouse is over us' if DraggableRectangle.lock is not self: return if event.inaxes != self.rect.axes: return x0, y0, w0, h0, aspect_ratio, xpress, ypress = self.press self.dx = event.xdata - xpress self.dy = event.ydata - ypress #self.rect.set_x(x0+dx) #self.rect.set_y(y0+dy) self.update_rect() canvas = self.rect.figure.canvas axes = self.rect.axes # restore the background region canvas.restore_region(self.background) # redraw just the current rectangle axes.draw_artist(self.rect) # blit just the redrawn area canvas.blit(axes.bbox) def on_release(self, event): 'on release we reset the press data' if DraggableRectangle.lock is not self: return self.press = None DraggableRectangle.lock = None # turn off the rect animation property and reset the background self.rect.set_animated(False) self.background = None # redraw the full figure self.rect.figure.canvas.draw() def disconnect(self): 'disconnect all the stored connection ids' self.rect.figure.canvas.mpl_disconnect(self.cidpress) self.rect.figure.canvas.mpl_disconnect(self.cidrelease) self.rect.figure.canvas.mpl_disconnect(self.cidmotion) def update_rect(self): x0, y0, w0, h0, aspect_ratio, xpress, ypress = self.press dx, dy = self.dx, self.dy bt = self.border_tol fixed_ar = self.fixed_aspect_ratio if (not self.allow_resize or (abs(x0+np.true_divide(w0,2)-xpress)<np.true_divide(w0,2)-bt*w0 and abs(y0+np.true_divide(h0,2)-ypress)<np.true_divide(h0,2)-bt*h0)): self.rect.set_x(x0+dx) self.rect.set_y(y0+dy) elif abs(x0-xpress)<bt*w0: self.rect.set_x(x0+dx) self.rect.set_width(w0-dx) if fixed_ar: dy = np.true_divide(dx, aspect_ratio) self.rect.set_y(y0+dy) self.rect.set_height(h0-dy) elif abs(x0+w0-xpress)<bt*w0: self.rect.set_width(w0+dx) if fixed_ar: dy = np.true_divide(dx, aspect_ratio) self.rect.set_height(h0+dy) elif abs(y0-ypress)<bt*h0: self.rect.set_y(y0+dy) self.rect.set_height(h0-dy) if fixed_ar: dx = dy*aspect_ratio self.rect.set_x(x0+dx) self.rect.set_width(w0-dx) elif abs(y0+h0-ypress)<bt*h0: self.rect.set_height(h0+dy) if fixed_ar: dx = dy*aspect_ratio self.rect.set_width(w0+dx) fig = plt.figure() ax = fig.add_subplot(111) rects = ax.bar(range(10), 20*np.random.rand(10)) drs = [] for rect in rects: dr = DraggableResizeableRectangle(rect) dr.connect() drs.append(dr) plt.show() ------------------------------------------------------------------------------ Join us December 9, 2009 for the Red Hat Virtual Experience, a free event focused on virtualization and cloud computing. 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