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solar: use lineXsphere from libgeometry.

--- a/solar.c

+++ b/solar.c

@@ -277,42 +277,6 @@

 	aimcamera(camera, p->body->p);

 }

-/*

- * ray-sphere (planet) intersection

- */

-int

-rayXsphere(Point3 *rp, Point3 p0, Point3 u, Point3 c, double r)

-{

-	Point3 dp;

-	double u·dp, Δ, d;

-	int n;

-

-	dp = subpt3(p0, c);

-	u·dp = dotvec3(u, dp);

-	if(u·dp > 0)	/* ignore what's behind */

-		return 0;

-

-	Δ = u·dp*u·dp - dotvec3(dp, dp) + r*r;

-	if(Δ < 0)		/* no intersection */

-		n = 0;

-	else if(Δ == 0){	/* tangent */

-		if(rp != nil){

-			d = -u·dp;

-			rp[0] = addpt3(p0, mulpt3(u, d));

-		}

-		n = 1;

-	}else{			/* secant */

-		if(rp != nil){

-			d = -u·dp + sqrt(Δ);

-			rp[0] = addpt3(p0, mulpt3(u, d));

-			d = -u·dp - sqrt(Δ);

-			rp[1] = addpt3(p0, mulpt3(u, d));

-		}

-		n = 2;

-	}

-	return n;

-}

-

 Point3

 identvshader(VSparams *sp)

 {

@@ -507,7 +471,7 @@

 void

 lmb(void)

 {

-	Point3 p0, u;

+	Point3 p0;

 	Point mp;

 	Planet *p;

 	Cmdbut *cmd;

@@ -520,12 +484,11 @@

 	mp = subpt(mctl->xy, screen->r.min);

 	if(ptinrect(mp, viewr)){

 		p0 = viewport2world(camera, Pt3(mp.x,mp.y,1,1));

-		u = normvec3(subpt3(p0, camera->p));

 		p = nil;

 		lastz = Inf(1);

 		for(i = 0; i < nelem(planets); i++)

-			if(rayXsphere(nil, p0, u, planets[i].body->p, planets[i].scale) > 0){

+			if(lineXsphere(nil, camera->p, p0, planets[i].body->p, planets[i].scale, 1) > 0){

 				z = vec3len(subpt3(planets[i].body->p, camera->p));

 				/* select the closest one */

 				if(z < lastz){