The clear alpha attribute indicates whether the alpha buffer, if one is bound to the current drawable, is cleared during renderer initialization. If you set clear alpha to True, then the alpha buffer is cleared to the alpha value specified in the renderer's background color, otherwise it is not. If the background color does not specify an alpha value, then the alpha value defaults to 1.0. Only pixels within the renderer's clip list are cleared. If you set clear alpha to True, and if the drawable associated with the renderer has the capability to support an alpha buffer, then an alpha buffer is allocated, if necessary.
The complete list of renderer attributes is listed in the Renderer Attributes Table.
For an overview about Renderers, see General Information. For a list of all Renderer functions and related topics, see Rendering.