Added kivy_memory_image.py example for entry: How to load an image from memory in Kivy

blog/kivy_memory_image.py

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+#!/usr/bin/env python
+# encoding: utf-8
+
+# kivy_memory_image.py
+# How to load an image from memory in Kivy
+# http://mornie.org/blog/2013/11/06/how-load-image-memory-kivy/
+
+# Copyright (c) 2013, Daniele Tricoli <eriol@mornie.org>
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+# 3. All advertising materials mentioning features or use of this software
+#    must display the following acknowledgement:
+#    This product includes software developed by the <organization>.
+# 4. Neither the name of the <organization> nor the
+#    names of its contributors may be used to endorse or promote products
+#    derived from this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY <COPYRIGHT HOLDER> ''AS IS'' AND ANY
+# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
+# DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+import StringIO
+
+from matplotlib.backends.backend_agg import FigureCanvasAgg
+from matplotlib.figure import Figure
+import numpy as np
+
+from kivy.app import App
+from kivy.core.image.img_pygame import ImageLoaderPygame
+from kivy.properties import ObjectProperty
+from kivy.uix.image import Image
+
+
+def cardioid(start, stop, step):
+    """A rotated cardioid."""
+    theta = np.arange(start, stop, step)
+    r = 1 - np.sin(theta)
+    return theta, r
+
+
+def polar_plot(theta, r, rmax):
+    """Draw a polat plot.
+
+    :returns: matplotlib.Figure
+    """
+    fig = Figure(facecolor='white')
+    ax = fig.add_subplot(111, polar=True, frameon=False)
+    ax.grid(False)
+    ax.set_xticklabels([])
+    ax.set_yticklabels([])
+    ax.plot(theta, r, color='g', linewidth=2)
+    ax.set_rmax(rmax)
+    return fig
+
+
+def fig2png(fig):
+    """Convert a matplotlib.Figure to PNG image.
+
+    :returns: PNG image bytes
+    """
+    data = StringIO.StringIO()
+    canvas = FigureCanvasAgg(fig)
+    canvas.print_png(data)
+    return data.getvalue()
+
+
+class MemoryImage(Image):
+    """Display an image already loaded in memory."""
+    memory_data = ObjectProperty(None)
+
+    def __init__(self, memory_data, **kwargs):
+        super(MemoryImage, self).__init__(**kwargs)
+
+        self.memory_data = memory_data
+
+    def on_memory_data(self, *args):
+        """Load image from memory."""
+        data = StringIO.StringIO(self.memory_data)
+        with self.canvas:
+            self.texture = ImageLoaderPygame(data).texture
+
+
+class TestApp(App):
+
+    def build(self):
+        return MemoryImage(self.options['image'])
+
+if __name__ == '__main__':
+
+    theta, r = cardioid(0, 8.0, 0.01)
+    image = fig2png(polar_plot(theta, r, 2.5))
+    TestApp(image=image).run()