Merge pull request #686 from kivy/core-widget-opacity

graphics/widget: introduce opacity attribute on the canvas and widget.

kivy/data/glsl/default.vs

@@ -1,6 +1,6 @@
 $HEADER$
 void main (void) {
-  frag_color = color;
+  frag_color = color * vec4(1.0, 1.0, 1.0, opacity);
   tex_coord0 = vTexCoords0;
   gl_Position = projection_mat * modelview_mat * vec4(vPosition.xy, 0.0, 1.0);
 }

kivy/data/glsl/header.vs

@@ -14,3 +14,4 @@ attribute vec2     vTexCoords0;
 uniform mat4       modelview_mat;
 uniform mat4       projection_mat;
 uniform vec4       color;
+uniform float      opacity;

kivy/graphics/instructions.pxd

@@ -82,6 +82,7 @@ cdef class CanvasBase(InstructionGroup):
 
 cdef class Canvas(CanvasBase):
     cdef object __weakref__
+    cdef float _opacity
     cdef CanvasBase _before
     cdef CanvasBase _after
     cdef void reload(self)
@@ -89,6 +90,7 @@ cdef class Canvas(CanvasBase):
     cpdef add(self, Instruction c)
     cpdef remove(self, Instruction c)
     cpdef draw(self)
+    cdef void apply(self)
 
 
 cdef class RenderContext(Canvas):

kivy/graphics/instructions.pyx

@@ -499,6 +499,7 @@ cdef class Canvas(CanvasBase):
     def __init__(self, **kwargs):
         get_context().register_canvas(self)
         CanvasBase.__init__(self, **kwargs)
+        self._opacity = kwargs.get('opacity', 1.0)
         self._before = None
         self._after = None
 
@@ -530,6 +531,19 @@ cdef class Canvas(CanvasBase):
         '''
         self.apply()
 
+    cdef void apply(self):
+        cdef float opacity = self._opacity
+        cdef float rc_opacity
+        cdef RenderContext rc
+        if opacity != 1.0:
+            rc = getActiveContext()
+            rc_opacity = rc['opacity']
+            rc.push_state('opacity')
+            rc['opacity'] = rc_opacity * opacity
+        InstructionGroup.apply(self)
+        if opacity != 1.0:
+            rc.pop_state('opacity')
+
     cpdef add(self, Instruction c):
         # the after group must remain the last one.
         if self._after is None:
@@ -569,6 +583,30 @@ cdef class Canvas(CanvasBase):
                 self._after = c
             return self._after
 
+    property opacity:
+        '''Property for get/set the opacity value of the canvas.
+
+        .. versionadded:: 1.4.1
+
+        The opacity attribute controls the opacity of the canvas and its
+        children.  Be careful, it's a cumulative attribute: the value is
+        multiplied to the current global opacity, and the result is applied to
+        the current context color.
+
+        For example: if your parent have an opacity of 0.5, and one children have an
+        opacity of 0.2, the real opacity of the children will be 0.5 * 0.2 = 0.1.
+
+        Then, the opacity is applied on the shader as::
+
+            frag_color = color * vec4(1.0, 1.0, 1.0, opacity);
+
+        '''
+        def __get__(self):
+            return self._opacity
+        def __set__(self, value):
+            self._opacity = value
+            self.flag_update()
+
 # Active Canvas and getActiveCanvas function is used
 # by instructions, so they know which canvas to add
 # tehmselves to
@@ -629,8 +667,8 @@ cdef class RenderContext(Canvas):
         self.default_texture = tex
 
         self.state_stacks = {
+            'opacity': [1.0],
             'texture0' : [0],
-            'linewidth': [1.0],
             'color'    : [[1.0,1.0,1.0,1.0]],
             'projection_mat': [Matrix()],
             'modelview_mat' : [Matrix()],

kivy/uix/widget.py

@@ -532,6 +532,30 @@ class Widget(EventDispatcher):
     dict.
     '''
 
+    opacity = NumericProperty(1.0)
+    '''Opacity of the widget and all the children.
+
+    .. versionadded:: 1.4.1
+
+    The opacity attribute controls the opacity of the widget and its children.
+    Be careful, it's a cumulative attribute: the value is multiplied to the
+    current global opacity, and the result is applied to the current context
+    color.
+
+    For example: if your parent have an opacity of 0.5, and one children have an
+    opacity of 0.2, the real opacity of the children will be 0.5 * 0.2 = 0.1.
+
+    Then, the opacity is applied on the shader as::
+
+        frag_color = color * vec4(1.0, 1.0, 1.0, opacity);
+
+    :data:`opacity` is a :class:`~kivy.properties.NumericProperty`, default to
+    1.0.
+    '''
+
+    def on_opacity(self, instance, value):
+        self.canvas.opacity = value
+
     canvas = None
     '''Canvas of the widget.