Re: [Visualpython-users] Opacity problem

[Bruce S. <Bru...@nc...>]

Many thanks for looking into this! I'll try it.

More generally, it would be a much healthier situation for VPython if 
more users would/could get involved at this level. Such help is greatly 
appreciated by everyone in the community.

Bruce Sherwood

CL wrote:
> About the opacity problem (crash when changing from opacity 1.0 to
> lower), it looks like it is a bug in frame.cpp
> 
> void frame::gl_render( const view& v)
> 
> ....
> 
> for (child_iterator i = children.begin(); i !=
> child_iterator(children.end()); ++i) {
> 	if (i->translucent()) {
> 		// See display_kernel::draw().
> 		trans_children.push_back( *i.base());
> 		i = children.erase(i.base());
> 		continue;
> 	}
> 
> 	i->outer_render(local);
> }
> 
> The code is trying to move a renderable from a list to another list
> when the opacity of the renderable is changing from 1.0 to something
> else. But children.erase() function returns the pointer after
> deletion, not the pointer before deletion.
> 
> Following similar logic in display_kernel::draw, replace the code with :
> 
> child_iterator i(children.begin());
> child_iterator i_end(children.end());
> while (i != i_end) {
> 	if (i->translucent()) {
> 		// See display_kernel::draw().
> 		trans_children.push_back( *i.base());
> 		i = children.erase(i.base());
> 		continue;
> 	}
> 	i->outer_render(local);
> 	i++;
> 
> It seems working on my simple test cases.
> 
> 
>> Don't I wish it were that simple. No, objects are created with
>> opacity=1.0 by default. That's why a scene contains opaque objects if
>> you don't explicitly set the opacity to something different.
> 
>> b = box()
>> print b.opacity # shows 1.0
> 
>> Bruce Sherwood
> 
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