Added a second effectwidget example

examples/widgets/effectwidget2.py

@@ -0,0 +1,52 @@
+'''
+This is an example of creating your own effect by writing a glsl string.
+'''
+
+from kivy.base import runTouchApp
+from kivy.lang import Builder
+from kivy.uix.effectwidget import EffectWidget, EffectBase
+
+
+# The effect string is glsl code defining an effect function.
+effect_string = '''
+vec4 effect(vec4 color, sampler2D texture, vec2 tex_coords, vec2 coords)
+{
+    // Note that time is a uniform variable that is automatically
+    // provided to all effects.
+    float red = color.x * abs(sin(time*2.0));
+    float green = color.y;  // No change
+    float blue = color.z * (1.0 - abs(sin(time*2.0)));
+    return vec4(red, green, blue, color.w);
+}
+'''
+
+
+class NewEffect(EffectBase):
+    def __init__(self, *args, **kwargs):
+        super(NewEffect, self).__init__(*args, **kwargs)
+        self.glsl = effect_string
+
+
+class DemoEffect(EffectWidget):
+    def __init__(self, *args, **kwargs):
+        self.effect_reference = NewEffect()
+        super(DemoEffect, self).__init__(*args, **kwargs)
+
+
+widget = Builder.load_string('''
+DemoEffect:
+    effects: [self.effect_reference] if checkbox.active else []
+    orientation: 'vertical'
+    Button:
+        text: 'Some text so you can see what happens.'
+    BoxLayout:
+        size_hint_y: None
+        height: dp(50)
+        Label:
+            text: 'Enable effect?'
+        CheckBox:
+            id: checkbox
+            active: True
+''')
+
+runTouchApp(widget)