multitexture: add tiny example showing multitexture capability

examples/canvas/multitexture.py

@@ -0,0 +1,68 @@
+'''
+Multitexturing
+==============
+'''
+
+from kivy.clock import Clock
+from kivy.app import App
+from kivy.uix.widget import Widget
+from kivy.core.window import Window
+from kivy.graphics import RenderContext, Color, Rectangle, BindTexture
+
+
+fs_multitexture = '''
+$HEADER$
+
+// New uniform that will receive texture at index 1
+uniform sampler2D texture1;
+
+void main(void) {
+
+    // multiple current color with both texture (0 and 1).
+    // currently, both will use exactly the same texture coordinates.
+    gl_FragColor = frag_color * \
+        texture2D(texture0, tex_coord0) * \
+        texture2D(texture1, tex_coord0);
+}
+'''
+
+
+class MultitextureWidget(Widget):
+
+    def __init__(self, **kwargs):
+        self.canvas = RenderContext()
+        self.canvas.shader.fs = fs_multitexture
+        with self.canvas:
+            Color(1, 1, 1)
+
+            # here, we are binding a custom texture at index 1
+            # this will be used as texture1 in shader.
+            BindTexture(source='mtexture2.png', index=1)
+
+            # create a rectangle with texture (will be at index 0)
+            Rectangle(size=(512, 512), source='mtexture1.png')
+
+        # set the texture1 to use texture index 1
+        self.canvas['texture1'] = 1
+
+        # call the constructor of parent
+        # if they are any graphics object, they will be added on our new canvas
+        super(MultitextureWidget, self).__init__(**kwargs)
+
+        # We'll update our glsl variables in a clock
+        Clock.schedule_interval(self.update_glsl, 0)
+
+    def update_glsl(self, *largs):
+        # This is needed for the default vertex shader.
+        self.canvas['projection_mat'] = Window.render_context['projection_mat']
+        self.canvas['modelview_mat'] = Window.render_context['modelview_mat']
+
+
+class MultitextureApp(App):
+
+    def build(self):
+        return MultitextureWidget()
+
+
+if __name__ == '__main__':
+    MultitextureApp().run()