Hello Jie,
Jie Liu wrote:
> However, when displaying the scene, the quad is pure red. What could be the
> problem? Will OpenSG blend the scene and the background?
> Or there are additional options to enable blending?
as David already explained, you need a BlendChunk on the material to
enable the blending and control the exact blend mode used.
Note also that OpenSG does back to front rendering of transparent
objects. However, it only sorts on the level of individual objects (i.e.
Geometries) not polygons (that would be very expensive as you'd need
to do depth peeling or something similar). To determine an objects
distance from the camera the center of the bounding box is used.
> =====================
> BTW, what is the right way to change the values of a GeoColors4f object.
> I checked some tutorial code, the manners to change the value of Nodecore
> objects are very confusing. Below are some examples.
>
> For a GeoTexCoords2f object, we can change its values in this way:
> tex->push_back(tex_value); // this seems the most common way, quite
> intuitive
this one goes through the generic interface of the properties and
converts the input data to a generic type and then back to the stored
type so for frequent/many changes it is less efficient than accessing
the field directly as in the next two examples. The advantage of the
generic interface is that you don't necessarily have to know the exact
type of a property which reduces the number of cases you have to handle
in generic code.
> however, for a GeoTexCoords1fPtr object, in this way:
> tex->*getField().*push_back(tex_value); // we have to get field before we
> push back values, why?
>
> As a constrast, for a GeoColors4f object, We have to do like this
> color->*getFieldPtr()->*push_back(color_value); // this time, we have
> to get the *pointer* of its field before we add values...
either way works and there is not really a difference. Since variables
of reference type must be initialized when defining them, it is
sometimes more convenient to use the pointer versions, especially if you
write code where a certain property may or may not be always present.
Cheers,
Carsten
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