R: [Plib-users] Drawing a simple triangle
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R: [Plib-users] Drawing a simple triangle
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From: Paolo L. <p.l...@ci...> - 2004-03-08 15:44:46
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Peter,
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:
ssgSimpleState *gen_state( char *tex_name )
{
ssgSimpleState *st =3D new ssgSimpleState () ;
// st -> setName( mat -> name );
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 );
st -> setShadeModel( GL_SMOOTH );
st -> disable( GL_BLEND );
st -> setOpaque();
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 );
return st ;
}
Such a state is ready to be set for the leaf n you generated:
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
Since the default in SSG is to enable back face culling, at our stage is
safer to disable it for our unknown-winding triangle:
n -> setCullFace( FALSE );
Note that face culling is set through a leaf method, not a state one.
Looking forward to hear about a "triangle born" -
Paolo
> -----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
> Thanks for your contribution. Unfortunately it still does not=20
> work :-( It may of course be that I have misunderstood your=20
> suggestion, in particular I am not sure that the yaw is correct.
>=20
> --- ssg_triangle.cc ---
>=20
> #define USE_SSG 1
>=20
> #include <GL/gl.h>
> #include <GL/glu.h>
>=20
> #include <plib/ssg.h>
> #include <SDL/SDL.h>
> #include <iostream>
>=20
> using namespace std;
>=20
> ssgRoot* scene;
> sgCoord camera;
> SGfloat pos_x, pos_y, pos_z, yaw =3D 0.0f, pitch =3D 0.0f, roll =3D =
0.0f;
>=20
>=20
> #define SCREEN_WIDTH 320
> #define SCREEN_HEIGHT 240
> #define SCREEN_BPP 24
>=20
> void init()
> {
> int videoFlags;
> SDL_Surface* surface;
>=20
> if ( SDL_Init( SDL_INIT_VIDEO ) < 0 ) {
> fprintf( stderr, "Video initialization failed:=20
> %s\n", SDL_GetError( ) );
> exit(0);
> }
>=20
> videoFlags =3D SDL_OPENGL;
> videoFlags |=3D SDL_GL_DOUBLEBUFFER;
> videoFlags |=3D SDL_HWPALETTE; =20
> videoFlags |=3D SDL_HWSURFACE;
> surface =3D SDL_SetVideoMode( SCREEN_WIDTH,=20
> SCREEN_HEIGHT, SCREEN_BPP, videoFlags );
>=20
> if ( !surface ) {
> fprintf( stderr, "Video mode set failed:=20
> %s\n", SDL_GetError( ) );
> exit(0);
> }
>=20
> #ifdef USE_SSG
> ssgInit();
> =09
> glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
> glEnable(GL_DEPTH_TEST);
>=20
> ssgVertexArray* vertices =3D new ssgVertexArray;
> sgVec3 x =3D { 0.5f, 2.5f , -0.25f };
> sgVec3 y =3D { -0.5f, 2.5f , -0.25f };
> sgVec3 z =3D { 0.0f, 1.5f , 0.75f };=20
> vertices->add(x);
> vertices->add(y);
> vertices->add(z);
>=20
> sgVec4 white =3D { 1.0f, 1.0f, 1.0f, 0.5f };
> ssgColourArray* colours =3D new ssgColourArray;
> colours->add(white);
> colours->add(white);
> colours->add(white);
> ssgNormalArray* normals =3D new ssgNormalArray(3);
> sgVec3 normal =3D { 0, -1.0f, 0 };
> normals->add(normal);
> normals->add(normal);
> normals->add(normal);
> ssgTexCoordArray* texs =3D new ssgTexCoordArray(3);
> sgVec2 tex_vec =3D {0,0};
> texs->add(tex_vec);
> texs->add(tex_vec);
> texs->add(tex_vec);
> =09
> ssgVtxTable* n =3D new ssgVtxTable(GL_TRIANGLES,=20
> vertices, normals, texs, colours);
> ssgTransform* trans =3D new ssgTransform;
> trans->addKid(n);
>=20
> scene =3D new ssgRoot;
> scene->addKid(trans);
>=20
> sgSphere *sp =3D scene->getBSphere();
> SGfloat radius =3D sp->getRadius();
> SGfloat EyeDist =3D float( radius * 1.f / tan( float(=20
> SCREEN_WIDTH/2 * 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
> #else
> glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
> glEnable(GL_DEPTH_TEST);
> #endif
> }
>=20
> void update()
> {
> glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT) ;
>=20
> #ifdef USE_SSG
> sgSetCoord( &camera, pos_x, pos_y, pos_z, yaw, pitch, roll );
> ssgSetCamera( &camera );
> ssgCullAndDraw(scene);
> #else
> glLoadIdentity();
> =09
> glColor3f(1.0f, 1.0f, 1.0f);
> glBegin(GL_TRIANGLES);
> glVertex2f(0.5f, -0.25f);
> glVertex2f(-0.5f, -0.25f);
> glVertex2f(0.0f, 0.75f);
> glEnd();
> #endif
> SDL_GL_SwapBuffers( );
> }
>=20
> int main(int argc, char *argv[])
> {
> init();
> for(unsigned int i =3D 0; i < 1000; i++) {
> update();
> }
> return 0;
> }
>=20
>=20
> > Hoping you'll also love Plib for its simplicity not payed with=20
> > completness -
>=20
> Me too :-)
>=20
> If somebody could write a small program that shows a triangle=20
> I would really be happy. It does not have to be using SDL, as=20
> I have a decent understanding of both glut and OpenGL (it is=20
> just ssg that is giving me problems).
>=20
> <snip>
>=20
> --=20
> Yours=20
> Peter Poulsen
>=20
>=20
>=20
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>=20
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