[Ves] Kiwi transparent background

[Jurre Hanema]

Hi,

I am developing an app based on the KiwiViewer code. Objects should be 
rendered on a transparent background instead of the standard blue one, 
such that another Android layer (a camera view, in this case) can be 
displayed behind it.

To achieve this, I have modified the function declaration and definition 
of vesKiwiBaseApp::setBackgroundColor() such as to expose the 
alpha-argument of vesRenderer::setBackgroundColor():

void vesKiwiBaseApp::setBackgroundColor(double r, double g, double b, 
double alpha)
{
   this->Internal->Renderer->setBackgroundColor(r, g, b, alpha);
}

In KiwiNative.cpp, I can now call app->setBackgroundColor() as follows:

bool loadDataset(const std::string& filename, int builtinDatasetIndex)
{
   // ...
   app->setBackgroundColor(255, 0, 0, 0);
   // ...
}

Alas, this changes the background color to solid red instead of 
transparency.

How to achieve rendering on a transparent background with Kiwi?

Regards,
Jurre