/* GL_shadow: an implementation of the stencil shadow volume technique * Copyright (C) 2005 Angelo "Encelo" Theodorou * * shadow.c: shadow and stencil related functions */#include <GL/gl.h>#include "object.h"#include "shadow.h"/* Draw the shadow of the object relative to a light in the stencil buffer */void CastShadow(Object *obj, GLfloat lightpos[4]){	int nf;	Plane *plane;	GLfloat side;	/* ----- Caculating face visibility ----- */	for(nf=0; nf < obj->nFaces; nf++){		plane = &obj->Faces[nf].pEq;		/* Calculating plane/light  distance*/		side = plane->a * lightpos[0] +			plane->b * lightpos[1] +			plane->c * lightpos[2] +			plane->d;		if (side > 0)			obj->Faces[nf].Visible = 1; /* True */		else			obj->Faces[nf].Visible = 0; /* False */	}/* ----- Performing stencil shadow volumes algorithm  ----- */	glPushAttrib( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_ENABLE_BIT		| GL_POLYGON_BIT | GL_STENCIL_BUFFER_BIT );	glDisable(GL_LIGHTING);	glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE); /* No output to the color buffer */	glDepthMask(GL_FALSE); /* Prevent writing in the depth buffer */	glDepthFunc(GL_LEQUAL);	glEnable(GL_STENCIL_TEST); /* Enabling stencil test */	glStencilFunc(GL_ALWAYS, 1, 0xFFFFFFFFL);	glEnable(GL_CULL_FACE);	/* First Pass - Increase stencil value in the shadow */	glCullFace(GL_BACK); /* or glFrontFace(GL_CCW) */	glStencilOp(GL_KEEP, GL_KEEP, GL_INCR);	ShadowVolume(obj, lightpos);	/* Second Pass. Decrease stencil value outside the shadow */	glCullFace(GL_FRONT); /* or glFrontFace(GL_CW) */	glStencilOp(GL_KEEP, GL_KEEP, GL_DECR);	ShadowVolume(obj, lightpos);	glPopAttrib();}/* Detects the silhouette edge of an object and project it towards infinity  * in the direction of object-light vector */void ShadowVolume(Object *obj, GLfloat lightpos[4]){	int nf, i;	Face *face;	int neighbour;	Point *v1, *v2, v3, v4; /* The four vertices of the extruded edge */	/* ----- Silhouette Edge ----- */		for (nf=0; nf < obj->nFaces; nf++ ){		face = &obj->Faces[nf];		if(face->Visible){			/* Extruding the silhouette */			for (i=0; i<3; i++){				neighbour = face->NeighIdx[i];				/* If there's no neighbour or its neighbouring face is invisible,				then this edge is part of the silhouette edge */				if (neighbour == -1 || !obj->Faces[neighbour].Visible){					v1 = &obj->Vertices[face->VertIdx[i]];					v2 = &obj->Vertices[face->VertIdx[(i+1)%3]];					/* Projecting this edge to "infinity" */					v3.x = (v1->x - lightpos[0]) * INF;					v3.y = (v1->y - lightpos[1]) * INF;					v3.z = (v1->z - lightpos[2]) * INF;	 				v4.x = (v2->x - lightpos[0]) * INF;					v4.y = (v2->y - lightpos[1]) * INF;					v4.z = (v2->z - lightpos[2]) * INF;					glBegin(GL_TRIANGLE_STRIP);					glVertex3f(v1->x, v1->y, v1->z);					glVertex3f(v1->x + v3.x, v1->y + v3.y, v1->z + v3.z);					/* Uncomment it for "real" infinity projection */					/* glVertex4f(v1->x + v3.x, v1->y + v3.y, v1->z + v3.z, 0.0f); */					glVertex3f(v2->x, v2->y, v2->z);					glVertex3f(v2->x + v4.x, v2->y + v4.y, v2->z + v4.z);					/* Uncomment it for "real" infinity projection */					/* glVertex4f(v2->x + v4.x, v2->y + v4.y, v2->z + v4.z, 0.0f); */					glEnd();				}			}		}	}}/* Draws a shadowing rectangle covering the entire screen */	void DrawShadow(void){	glPushAttrib( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_ENABLE_BIT		| GL_POLYGON_BIT | GL_STENCIL_BUFFER_BIT );	glDisable(GL_LIGHTING);	glColor4f(0.0f, 0.0f, 0.0f, 0.4f);	glEnable(GL_BLEND);	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);	glEnable(GL_STENCIL_TEST);	glStencilFunc(GL_NOTEQUAL, 0, 0xFFFFFFFFL);	glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);	glPushMatrix();	glLoadIdentity();	glBegin(GL_TRIANGLE_STRIP);		glVertex3f(-0.1f, 0.1f,-0.1f);		glVertex3f(-0.1f,-0.1f,-0.1f);		glVertex3f( 0.1f, 0.1f,-0.1f);		glVertex3f( 0.1f,-0.1f,-0.1f);	glEnd();	glPopMatrix();		glPopAttrib();}