Re: [Mesa3d-dev] Re: [Dri-devel] Mesa C++ driver framework update

[Keith W. <ke...@tu...>]

Felix K=FChling wrote:
> On Mon, 10 Mar 2003 22:23:07 +0000
> Jos=E9 Fonseca <jrf...@tu...> wrote:
> [snip]
>=20
>>As I said above this can be done in C++, and without damage to
>>efficiency.
>>
>>Imagine you have a TnL abstract class:
>>
>>class TNL {
>>  // A OpenGL function
>>  virtual void Coord3f(GLfloat x, GLfloat y, GLfloat z) =3D 0;
>> =20
>>  // Activate
>>  virtual void activate() =3D 0;
>>
>>  protected:
>>    struct dispatch_table *my_dispatch_table;
>>} ;
>>
>>and then you have two inherited classes for software and hardware
>>rendering:
>>
>>class SoftwareTNL : public TNL {
>>  // The software version. Note the _inline_
>>  inline void Coord3f(x, y, z) {
>>    _mesa_swrast_deal_with_this_vertex(x, y, z);
>>  }
>>};
>>
>>class HardwareTNL : public TNL {
>>  // The hardware version. Note the _inline_
>>  inline void Coord3f(x, y, z) {
>>    _add_vertex_to_DMA_buffer(x, y, z);
>>  }
>>};
>>
>>and then the C-callable versions for the glapi disptach table:
>>
>>void softwareCoord3f(GLcontext *ctx, GLfloat x, GLfloat y, GLfloat z) {
>>  Driver::Context *context =3D ctx;
>>  Driver::SoftwareTNL &tnl =3D ctx->tnl;
>>
>>  // There will be no call as the function will be expanded inline
>>  tnl.Coord3F(x, y, z);
>>}
>=20
>=20
> Here you're converting a GLcontext * to a Driver::Context *. Can you do
> that because Mesa::Context has GLcontext as first member? Anyway, if
> that didn't work you could always do some fancy pointer arithmetics wit=
h
> the offset of the GLcontext in Driver::Context.

There's a slight misconception happening here -- the 'ctx' argument doesn=
't=20
exist.  The function should read something like:

	void swv3f( GLfloat x, GLfloat y, GLfloat z )
	{
		GET_CONTEXT_FROM_THREAD_LOCAL_STORE( ctx )
		// get tnl somehow
=09
		tnl->v3f( x, y, z )
	}

But why bother?  tnl->v3f isn't virtual, so what's the point of having th=
e=20
implementation somewhere else?  Why not just do it here?

Keith