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Hi, In main loop for first : I visualize all objects and for second : use SHADOW_FOR_OBJECT() for all objects.
my depth pass stencil shadow algorithm for shadow cast is here :

void SHADOW_FOR_OBJECT(object obj, float lp[4]) //lp = light position{ unsigned int	i, j, k, jj; unsigned int	p1=0, p2=0; vertex		v1, v2, v3, v4; float		side; for (i=0; i < obj.number_of_faces; i++) {		// chech to see if light is in front or behind the plane (face plane)  side = obj.faces[i].ro_no.a*lp[0] + obj.faces[i].ro_no.b*lp[1] + obj.faces[i].ro_no.c*lp[2] + obj.faces[i].ro_no.d*lp[3];  if (side > 0.0) obj.faces[i].light_visible = 1; else obj.faces[i].light_visible = 0; } glEnable(GL_BLEND); glDisable(GL_LIGHTING); glDisable(GL_TEXTURE_2D); glDepthMask(GL_FALSE); glDepthFunc(GL_LEQUAL); glEnable(GL_DEPTH_TEST); glEnable(GL_STENCIL_TEST); glColorMask(0, 0, 0, 0); glStencilFunc(GL_ALWAYS, 1, 0xffffffff); glEnable(GL_CULL_FACE); glCullFace(GL_BACK); glStencilOp(GL_KEEP, GL_KEEP, GL_INCR); for (i=0; i < obj.number_of_faces; i++) {  if (obj.faces[i].light_visible)  {   for (j=0; j<3; j++)   {	k = obj.faces[i].conectivity[j];	if ((!k) || (!obj.faces[k-1].light_visible))    {      v1.x = obj.vertex[obj.faces[i].vertex_index[j]].x;      v1.y = obj.vertex[obj.faces[i].vertex_index[j]].y;      v1.z = obj.vertex[obj.faces[i].vertex_index[j]].z; 	  v2.x = obj.vertex[obj.faces[i].vertex_index[(j+1)%3]].x;      v2.y = obj.vertex[obj.faces[i].vertex_index[(j+1)%3]].y;      v2.z = obj.vertex[obj.faces[i].vertex_index[(j+1)%3]].z;      v3.x = (v1.x - lp[0]);	  v3.y = (v1.y - lp[1]);	  v3.z = (v1.z - lp[2]);	  v4.x = (v2.x - lp[0]);	  v4.y = (v2.y - lp[1]);	  v4.z = (v2.z - lp[2]);      glBegin(GL_TRIANGLE_STRIP);	  glVertex3f(v1.x, v1.y, v1.z);      glVertex4f(v3.x, v3.y, v3.z, 0.0);      glVertex3f(v2.x, v2.y, v2.z);	  glVertex4f(v4.x, v4.y, v4.z, 0.0);	  glEnd();    }   }  } }	// second pass, stencil operation increases stencil value glCullFace(GL_FRONT); glStencilOp(GL_KEEP, GL_KEEP, GL_DECR);for (i=0; i < obj.number_of_faces; i++) {  if (obj.faces[i].light_visible)  {   for (j=0; j<3; j++)   {	k = obj.faces[i].conectivity[j];	if ((!k) || (!obj.faces[k-1].light_visible))    {      v1.x = obj.vertex[obj.faces[i].vertex_index[j]].x;      v1.y = obj.vertex[obj.faces[i].vertex_index[j]].y;      v1.z = obj.vertex[obj.faces[i].vertex_index[j]].z; 	  v2.x = obj.vertex[obj.faces[i].vertex_index[(j+1)%3]].x;      v2.y = obj.vertex[obj.faces[i].vertex_index[(j+1)%3]].y;      v2.z = obj.vertex[obj.faces[i].vertex_index[(j+1)%3]].z;	  /// Projecting this edge to "infinity"      v3.x = (v1.x - lp[0]);	  v3.y = (v1.y - lp[1]);	  v3.z = (v1.z - lp[2]);	  v4.x = (v2.x - lp[0]);	  v4.y = (v2.y - lp[1]);	  v4.z = (v2.z - lp[2]);      glBegin(GL_TRIANGLE_STRIP);	  glVertex3f(v1.x, v1.y, v1.z);      glVertex4f(v3.x, v3.y, v3.z, 0.0);      glVertex3f(v2.x, v2.y, v2.z);	  glVertex4f(v4.x, v4.y, v4.z, 0.0);	  glEnd();    }   }  } }}

At the finish in main loop apply two rectangle :
glCullFace(GL_BACK);  glColorMask(1, 1, 1, 1);  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);  glStencilFunc(GL_NOTEQUAL, 0, 0xffffffff);  glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);  glPushMatrix();  glLoadIdentity();  glColor4f(0.0, 0.0, 0.0, 0.1);  //first  glBegin(GL_TRIANGLE_STRIP);  glVertex3f(-0.1, 0.1,-0.1);  glVertex3f(-0.1,-0.1,-0.1);  glVertex3f( 0.1, 0.1,-0.1);  glVertex3f( 0.1,-0.1,-0.1);  glEnd();  glPopMatrix();  glDisable(GL_BLEND);  glDepthMask(GL_TRUE);  glDisable(GL_STENCIL_TEST);  glEnable(GL_TEXTURE_2D);  glPushMatrix();  glLoadIdentity();  glColor4f(0.7, 0.6, 0.95, 1.0);  //second    glBegin(GL_TRIANGLE_STRIP);   glVertex3f(-1000.0, 1000.0,-1000.0);  glVertex3f(-1000.0,-1000.0,-1000.0);  glVertex3f( 1000.0, 1000.0,-1000.0);  glVertex3f( 1000.0,-1000.0,-1000.0);  glEnd();  glPopMatrix();  glEnable(GL_LIGHTING);

Here is set up for conectivity function :
void SETUP_CONECTIVITY(object *obj){ unsigned int p1i, p2i, p1j, p2j; unsigned int P1i, P2i, P1j, P2j; unsigned int i,j,ki,kj; for(i=0; i<obj->number_of_faces-1; i++)  for(j=i+1; j<obj->number_of_faces; j++)   for(ki=0; ki<3; ki++)	if( !obj->plochy[i].conectivity[ki])    {	 for( kj=0; kj<3; kj++)     {	  p1i=ki;	  p1j=kj;	  p2i=(ki+1)%3;	  p2j=(kj+1)%3;	  p1i=obj->faces[i].vertex_index[p1i];	  p2i=obj->faces[i].vertex_index[p2i];	  p1j=obj->faces[j].vertex_index[p1j];	  p2j=obj->faces[j].vertex_index[p2j];      P1i=((p1i+p2i)-abs(p1i-p2i))/2;	  P2i=((p1i+p2i)+abs(p1i-p2i))/2;      P1j=((p1j+p2j)-abs(p1j-p2j))/2;	  P2j=((p1j+p2j)+abs(p1j-p2j))/2;	  if ((P1i==P1j) && (P2i==P2j))      {  //they are neighbours	   obj->faces[i].conectivity[ki] = j+1;	   obj->faces[j].conectivity[kj] = i+1;	  } 	 }    }}

And plane for all faces in obect :
void PLANE_OF_FACE(object *obj){ vertex v1, v2, v3; int p; for (p=0; p<obj->number_of_faces; p++) {  v1.x = obj->vertex[obj->faces[p].vertex_index[0]].x;  v1.y = obj->vertex[obj->faces[p].vertex_index[0]].y;  v1.z = obj->vertex[obj->faces[p].vertex_index[0]].z;  v2.x = obj->vertex[obj->faces[p].vertex_index[1]].x;  v2.y = obj->vertex[obj->faces[p].vertex_index[1]].y;  v2.z = obj->vertex[obj->faces[p].vertex_index[1]].z;  v3.x = obj->vertex[obj->faces[p].vertex_index[2]].x;  v3.y = obj->vertex[obj->faces[p].vertex_index[2]].y;  v3.z = obj->vertex[obj->faces[p].vertex_index[2]].z;  obj->faces[p].ro_no.a = v1.y*(v2.z-v3.z) + v2.y*(v3.z-v1.z) + v3.y*(v1.z-v2.z);  obj->faces[p].ro_no.b = v1.z*(v2.x-v3.x) + v2.z*(v3.x-v1.x) + v3.z*(v1.x-v2.x);  obj->faces[p].ro_no.c = v1.x*(v2.y-v3.y) + v2.x*(v3.y-v1.y) + v3.x*(v1.y-v2.y);  obj->faces[p].ro_no.d = - (v1.x*(v2.y*v3.z-v3.y*v2.z)   		                   + v2.x*(v3.y*v1.z-v1.y*v3.z)    		               + v3.x*(v1.y*v2.z-v2.y*v1.z)); }}

Maybe it will help.

[Edited by - Christobal_de_M on February 24, 2010 1:22:02 PM]

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