Re: [Plib-users] Drawing a simple triangle

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

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

> Peter,
> 
> on my opinion you just missed to set up a camera for looking at scene
> objects. It can be done this way:
> 
> #include <plib/sg.h>
> 
> 	sgCoord camera;
> 	SGfloat pos_x, pos_y, pos_z, yaw, pitch, roll;
> 
> 	// set pos_x, pos_y, pos_z, yaw, pitch and roll to some suitable
> values
> 	// then, before ssgCullAndDraw, actually set the SSG camera
> 	sgSetCoord( camera, pos_x, pos_y, pos_z, yaw, pitch, roll );
> 	ssgSetCamera( &camera );
> 
> SG is the prefix for the Plib math/geometry library stuffs.
> 
> Finding a plausible position for the init view (given a scene, in
> general, you could not know its extent along the three axes) it's a
> question of taste - I could suggest this:
> 
> 	sgSphere *sp = scene->getBSphere();
> 	SGfloat radius = sp->getRadius();
> 	SGfloat EyeDist = float( radius * 1.f / tan( float( fov_x/2 *
> SG_DEGREES_TO_RADIANS ) ) );
> 	SGfloat Ex, Ey, Ez;
> 
> 	pos_x = sp->getCenter()[0];
> 	pos_y = sp->getCenter()[1] + EyeDist;
> 	pos_z = sp->getCenter()[2];
> 
> Then, moving in 3D above or around the scene is a matter of changing
> those six parameters to the sgSetCoord/ssgSetCamera (yaw is compass
> heading, pitch rotates around the screen x-axis, roll around the axis
> norma to the screen).
> 
Thanks for your contribution. Unfortunately it still does not work :-(
It may of course be that I have misunderstood your suggestion, in
particular I am not sure that the yaw is correct.

--- 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;
sgCoord camera;
SGfloat pos_x, pos_y, pos_z, yaw = 0.0f, pitch = 0.0f, roll = 0.0f;


#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);

	ssgVertexArray* vertices = new ssgVertexArray;
	sgVec3 x = { 0.5f, 2.5f , -0.25f };
	sgVec3 y = { -0.5f, 2.5f , -0.25f };
	sgVec3 z = { 0.0f, 1.5f , 0.75f }; 
	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 };
	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);

	sgSphere *sp = scene->getBSphere();
	SGfloat radius = sp->getRadius();
	SGfloat EyeDist = float( radius * 1.f / tan( float( SCREEN_WIDTH/2 * SG_DEGREES_TO_RADIANS ) ) );
	SGfloat Ex, Ey, Ez;

	pos_x = sp->getCenter()[0];
	pos_y = sp->getCenter()[1] + EyeDist;
	pos_z = sp->getCenter()[2];

#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
	sgSetCoord( &camera, pos_x, pos_y, pos_z, yaw, pitch, roll );
	ssgSetCamera( &camera );
	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;
}


> Hoping you'll also love Plib for its simplicity not payed with
> completness -

Me too :-)

If somebody could write a small program that shows a triangle I would
really be happy. It does not have to be using SDL, as I have a decent
understanding of both glut and OpenGL (it is just ssg that is giving me problems).

<snip>

-- 
Yours 
Peter Poulsen