Re: R: [Plib-users] Drawing a simple triangle

[Peter P. <pet...@st...>]

"Paolo Leoncini" <p.l...@ci...> writes:

Wee!!! Thanks, it works!!
> Peter,
>=20
> Ok, one step forward - let's set a state for the geometry (leaf) node.
> For a leaf (ssgVTable, ssgVtxTable, or ssgVtxArray) a state tells OpenGL
> about object material (properties, texture) as well as modes to
> enable/disable.
> The following code generates and returns a state with safe defaults:
>=20
> ssgSimpleState *gen_state( char *tex_name )
> {
> 	ssgSimpleState *st =3D new ssgSimpleState () ;
>=20
> //	st -> setName( mat -> name );
>=20
> 	st -> setMaterial ( GL_AMBIENT, 1.0f, 1.0f, 1.0f, 1.0f );
> 	st -> setMaterial ( GL_DIFFUSE, 1.0f, 1.0f, 1.0f, 1.0f );
> 	st -> setMaterial ( GL_SPECULAR, 0, 0, 0, 1 );
> 	st -> setMaterial ( GL_EMISSION, 0, 0, 0, 1 );
>=20
> 	st -> setShadeModel( GL_SMOOTH );
> 	st -> disable( GL_BLEND );
> 	st -> setOpaque();
>=20
> 	if ( tex_name !=3D NULL ) {
> 		ssgTexture *tex =3D new ssgTexture(tex_name, 0, 0, 1);
> 		if ( tex )
> 			st -> setTexture( tex );
> 		else
> 			fprintf( stderr, "can't load texture from image
> file %s\n", tex_name );
> 		st -> enable( GL_TEXTURE_2D );
> 	} else
> 		st -> disable( GL_TEXTURE_2D );
>=20
> 	return st ;
> }
>=20
> Such a state is ready to be set for the leaf n you generated:
>=20
> 	ssgSimpleState *s =3D gen_state( NULL /* tex_name */ );	// you
> have set null tex coords, so it's better to not map any texture
> 	n -> setState( s );
> 	s -> enable( GL_LIGHTING );		// or could disable it
> if you supply good normals
> 	s -> disable( GL_COLOR_MATERIAL );	// or could enable it if
> you supply per-vertex colors
>=20
> Since the default in SSG is to enable back face culling, at our stage is
> safer to disable it for our unknown-winding triangle:
>=20
> 	n -> setCullFace( FALSE );
>=20
> Note that face culling is set through a leaf method, not a state one.
>=20
> Looking forward to hear about a "triangle born" -
>=20
> Paolo
>=20
>=20
> > -----Messaggio originale-----
> > Da: pli...@li...=20
> > [mailto:pli...@li...] Per conto di=20
> > Peter Poulsen
> > Inviato: luned=EC 8 marzo 2004 15.56
> > A: pli...@li...
> > Oggetto: Re: [Plib-users] Drawing a simple triangle
> >=20
> >=20
> > "Paolo Leoncini" <p.l...@ci...> writes:
> >=20
> > > Peter,
> > >=20
> > > on my opinion you just missed to set up a camera for=20
> > looking at scene=20
> > > objects. It can be done this way:
> > >=20
> > > #include <plib/sg.h>
> > >=20
> > > 	sgCoord camera;
> > > 	SGfloat pos_x, pos_y, pos_z, yaw, pitch, roll;
> > >=20
> > > 	// set pos_x, pos_y, pos_z, yaw, pitch and roll to some=20
> > suitable=20
> > > values
> > > 	// then, before ssgCullAndDraw, actually set the SSG camera
> > > 	sgSetCoord( camera, pos_x, pos_y, pos_z, yaw, pitch, roll );
> > > 	ssgSetCamera( &camera );
> > >=20
> > > SG is the prefix for the Plib math/geometry library stuffs.
> > >=20
> > > Finding a plausible position for the init view (given a scene, in=20
> > > general, you could not know its extent along the three axes) it's a=20
> > > question of taste - I could suggest this:
> > >=20
> > > 	sgSphere *sp =3D scene->getBSphere();
> > > 	SGfloat radius =3D sp->getRadius();
> > > 	SGfloat EyeDist =3D float( radius * 1.f / tan( float( fov_x/2 *=20
> > > SG_DEGREES_TO_RADIANS ) ) );
> > > 	SGfloat Ex, Ey, Ez;
> > >=20
> > > 	pos_x =3D sp->getCenter()[0];
> > > 	pos_y =3D sp->getCenter()[1] + EyeDist;
> > > 	pos_z =3D sp->getCenter()[2];
> > >=20
> > > Then, moving in 3D above or around the scene is a matter of=20
> > changing=20
> > > those six parameters to the sgSetCoord/ssgSetCamera (yaw is compass=20
> > > heading, pitch rotates around the screen x-axis, roll=20
> > around the axis=20
> > > norma to the screen).
> > >=20

--=20
Yours=20
Peter Poulsen