Re: [Plib-users] Drawing a simple triangle

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

Steve Baker <sjb...@ai...> writes:

> Peter Poulsen wrote:
> > I have tried the program below, but it only shows a black screen. Can
> > anybody explain why? The program works if I make direct gl-calls (just
> > comment out the first line).
> 
> SSG uses the 'Z-is-up' convention - so I guess your polygon is edge-on.
> Also, SSG defaults to perspective rendering - so it'll be near-plane
> clipped.

Thanks. I have now tried to modify the program, but it still does not
work :-) I'm sorry for bothering you with this trivil matter, but if I
cannot get that to work, I probably cannot get a "real" program to work.

--- ssg_triangle.cc ---

#define USE_SSG 1

#include <GL/gl.h>
#include <GL/glu.h>

#include <plib/ssg.h>
#include <SDL/SDL.h>
#include <iostream>

using namespace std;

ssgRoot* scene;
#define SCREEN_WIDTH 320
#define SCREEN_HEIGHT 240
#define SCREEN_BPP 24

void init()
{
	int videoFlags;
	SDL_Surface* surface;

	if ( SDL_Init( SDL_INIT_VIDEO ) < 0 ) {
		fprintf( stderr, "Video initialization failed: %s\n",  SDL_GetError( ) );
		exit(0);
	}

	videoFlags  = SDL_OPENGL;
	videoFlags |= SDL_GL_DOUBLEBUFFER;
	videoFlags |= SDL_HWPALETTE;      
	videoFlags |= SDL_HWSURFACE;
	surface = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, videoFlags );

	if ( !surface ) {
		fprintf( stderr,  "Video mode set failed: %s\n", SDL_GetError( ) );
		exit(0);
	}

#ifdef USE_SSG
	ssgInit();
	
	glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f ) ;
	glEnable ( GL_DEPTH_TEST ) ;
	ssgGetCurrentContext()->setFOV    (60.0f, 0.0f);   // New
	ssgGetCurrentContext()->setNearFar(0.1f, 70.0f);   // New

	ssgVertexArray* vertices = new ssgVertexArray;
	sgVec3 x = { 0.5f, 0.5f , -0.25f};                 // Changed
	sgVec3 y = { -0.5f, 0.5f , -0.25f };               // Changed
	sgVec3 z = { 0.0f, 0.5f , 0.75f };                 // Changed
	vertices->add(x);
	vertices->add(y);
	vertices->add(z);

	sgVec4 white = { 1.0f, 1.0f, 1.0f, 0.5f };
	ssgColourArray* colours = new ssgColourArray;
	colours->add(white);
	colours->add(white);
	colours->add(white);
	ssgNormalArray* normals = new ssgNormalArray(3);
	sgVec3 normal = { 0, -1.0f, 0 };                   // Changed
	normals->add(normal);
	normals->add(normal);
	normals->add(normal);
	ssgTexCoordArray* texs = new ssgTexCoordArray(3);
	sgVec2 tex_vec = {0,0};
	texs->add(tex_vec);
	texs->add(tex_vec);
	texs->add(tex_vec);
	
	ssgVtxTable* n = new ssgVtxTable(GL_TRIANGLES, vertices, normals, texs, colours);
	ssgTransform* trans = new ssgTransform;
	trans->addKid(n);

	scene = new ssgRoot;
	scene->addKid(trans);
#else
	glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f ) ;
	glEnable ( GL_DEPTH_TEST ) ;
#endif
}

void update()
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT) ;

#ifdef USE_SSG
	ssgCullAndDraw(scene);

#else
	glLoadIdentity();
	
	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( );
}

int main(int argc, char *argv[])
{
	init();
	for(unsigned int i = 0; i < 1000; i++) {
		update();
	}
	return 0;
}

-- 
Yours 
Peter Poulsen