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On 2013-10-29 13:39, Claude Heiland-Allen wrote:

Hi,

I want to write a new Geo.

Looking for a tutorial, I found the documentation at gem/doc/manual/WriteCode.html which essentially says "use the source, Luke". But 140k lines of code are quite daunting...

ahja, this document has not been touched since i took over Gem 13 or so years ago...

Where should I start?

derive your object-class from GemBasse

I need 3 methods, respectively called

after OpenGL context creation,

virtual void startRendering();

at render time

virtual void render(GemState *state);

and before context destruction.

virtual void stopRendering();

to there's also a virtual bool isRunnable(); that get's called (usually once) for each context so you can add some checks whether the current openGL-context provides everything you need: if isRunnable() returns FALSE, the object will not be part of the rendering chain. (this is mainly to prevent continuous triggers of invalid calls)

start/stopRendering is not really tied to context creation/destruction but to turning rendering on/off (which has been enough for most use-case so far) once the multi-context support is finished, stopRendering() will also be called if a context is destroyed.

in order to make your object multi-context aware, you should use gem::ContextData for any per-context variable.

something like: gem::ContextData<GLenum>m_id;

in most cases, you can use `m_id` just as if it was a GLenum (that is: the template-argument type), but it will hold a different value for each context.

hope this helps.

fgmasdr IOhannes