games/galaxy: fix zoom

Zooming when far away from the center of gravity
of the galaxy would zoom the center of the screen
out of view. Now adjust the origin so that the
center of the screen stays centered

3 files changed, 52 insertions, 32 deletions

diff --git a/sys/src/games/galaxy/body.c b/sys/src/games/galaxy/body.c
index ea610ad56..a085a77db 100644
--- a/sys/src/games/galaxy/body.c
+++ b/sys/src/games/galaxy/body.c
@@ -31,14 +31,23 @@ body(void)
 	return b;
 }
 
+Point
+topoint(Vector v)
+{
+	Point p;
+
+	p.x = v.x/scale + orig.x;
+	p.y = v.y/scale + orig.y;
+	return p;
+}
+
 void
 drawbody(Body *b)
 {
 	Point pos, v;
 	int s;
 
-	pos.x = b->x / scale + orig.x;
-	pos.y = b->y / scale + orig.y;
+	pos = topoint(b->Vector);
 	s = b->size/scale;
 	fillellipse(screen, pos, s, s, b->col, ZP);
 	v.x = b->v.x/scale*10;
diff --git a/sys/src/games/galaxy/galaxy.c b/sys/src/games/galaxy/galaxy.c
index d81b34123..8323e94da 100644
--- a/sys/src/games/galaxy/galaxy.c
+++ b/sys/src/games/galaxy/galaxy.c
@@ -171,8 +171,7 @@ drawglxy(void)
 
 	draw(screen, screen->r, display->black, 0, ZP);
 	for(b = glxy.a; b < glxy.a + glxy.l; b++) {
-		pos.x = b->x / scale + orig.x;
-		pos.y = b->y / scale + orig.y;
+		pos = topoint(b->Vector);
 		s = b->size/scale;
 		fillellipse(screen, pos, s, s, b->col, ZP);
 		if(showv) {
@@ -198,8 +197,7 @@ setsize(Body *b)
 	Point pos, d;
 	double h;
 
-	pos.x = b->x / scale + orig.x;
-	pos.y = b->y / scale + orig.y;
+	pos = topoint(b->Vector);
 	d = subpt(mc->xy, pos);
 	h = hypot(d.x, d.y);
 	b->size = h == 0 ? scale : h*scale;
@@ -211,18 +209,10 @@ setvel(Body *b)
 {
 	Point pos, d;
 
-	pos.x = b->x / scale + orig.x;
-	pos.y = b->y / scale + orig.y;
+	pos = topoint(b->Vector);
 	d = subpt(mc->xy, pos);
-	b->v.x = (double)d.x*scale/10;
-	b->v.y = (double)d.y*scale/10;
-}
-
-void
-setpos(Body *b)
-{
-	b->x = (mc->xy.x - orig.x) * scale;
-	b->y = (mc->xy.y - orig.y) * scale;
+	b->v.x = d.x*scale/10;
+	b->v.y = d.y*scale/10;
 }
 
 void
@@ -275,7 +265,6 @@ dobody(void)
 	}
 
 	b = body();
-	setpos(b);
 	setvel(b);
 	setsize(b);
 	b->col = randcol();
@@ -290,7 +279,7 @@ dobody(void)
 		else if(mc->buttons == 5)
 			dovel(b);
 		else
-			setpos(b);
+			b->Vector = tovector(mc->xy);
 	}
 
 	CHECKLIM(b, f);
@@ -349,30 +338,41 @@ domove(void)
 	setcursor(mc, cursor);
 }
 
+Point
+screencenter(void)
+{
+	Point sc;
+
+	sc = divpt(subpt(screen->r.max, screen->r.min), 2);
+	return addpt(screen->r.min, sc);
+}
+
 void
 dozoom(void)
 {
-	Point z, d;
-	double f, olds;
+	Point oxy, d, sc, off;
+	Vector gsc;
+	double z, oscale;
 
 	setcursor(mc, &zoomcursor);
-
-	z = mc->xy;
-	olds = scale;
+	oxy = mc->xy;
+	oscale = scale;
 	for(;;) {
 		readmouse(mc);
 		if(mc->buttons != 2)
 			break;
-		d = subpt(mc->xy, z);
-		f = tanh((double)d.y/200) + 1;
+		d = subpt(mc->xy, oxy);
+		z = tanh((double)d.y/200) + 1;
+		sc = screencenter();
+		gsc = tovector(sc);
 		pause(0, 0);
-		scale = f*olds;
+		scale = z*oscale;
+		off = subpt(topoint(gsc), sc);
+		orig = subpt(orig, off);
 		drawglxy();
 		pause(1, 0);
 	}
-
 	setcursor(mc, cursor);
-	pause(1, 0);
 }
 
 void
@@ -579,6 +579,16 @@ Again:
 	}
 }
 
+Vector
+tovector(Point p)
+{
+	Vector v;
+
+	v.x = (p.x-orig.x) * scale;
+	v.y = (p.y-orig.y) * scale;
+	return v;
+}
+
 void
 usage(void)
 {
@@ -632,8 +642,7 @@ threadmain(int argc, char **argv)
 		sysfatal("initmouse failed: %r");
 
 	dt² = dt*dt;
-	orig = divpt(subpt(screen->r.max, screen->r.min), 2);
-	orig = addpt(orig, screen->r.min);
+	orig = screencenter();
 	glxyinit();
 	quadsinit();
 	if(doload)
diff --git a/sys/src/games/galaxy/galaxy.h b/sys/src/games/galaxy/galaxy.h
index bf9b5cfec..1e178ac09 100644
--- a/sys/src/games/galaxy/galaxy.h
+++ b/sys/src/games/galaxy/galaxy.h
@@ -55,14 +55,16 @@ Body ZB;
 QB space;
 
 Image *randcol(void);
+Point topoint(Vector);
+Vector tovector(Point);
 
 Body *body(void);
 void drawbody(Body*);
 Vector center(void);
 void glxyinit(void);
+int Bfmt(Fmt*);
 void readglxy(int);
 void writeglxy(int);
-int Bfmt(Fmt*);
 
 void quadcalc(Body*, QB, double);
 int quadins(Body*, double);