From 2764155d15eeca9715b2428fa8653cc35ed7cb79 Mon Sep 17 00:00:00 2001
From: Werner Almesberger <werner@openmoko.org>
Date: Fri, 24 Sep 2010 17:28:48 -0300
Subject: [PATCH] Increase dynamic range of rotation and follow "far from
 center = faster" paradigm.

- solidify/overlap.c (scroll_event): make weighting of rotation exponential,
  so we can both adjust precisely and spin rapidly. Also reverse weighting
  to rotate more quickly on the outside.
- solidify/style.h (SLOWEST_ROT, FASTEST_ROT): parameters for weighting of
  rotation
---
 solidify/overlap.c | 23 +++++++++++++++++++++--
 solidify/style.h   |  2 ++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/solidify/overlap.c b/solidify/overlap.c
index cebf03c..960fc47 100644
--- a/solidify/overlap.c
+++ b/solidify/overlap.c
@@ -362,24 +362,43 @@ static gboolean scroll_event(GtkWidget *widget, GdkEventScroll *event,
 	int dy = event->y-sy(s)/2;
 	double r = hypot(dx, dy);
 	double rc = r_center(s);
+	double rs, rot;
 	int center = r < rc;
 	int osd = osd_proximity(s, dx, dy);
 
 	if (r < 1)
 		return TRUE;
+
+	/*
+	 * rot goes exponentially from SLOWEST_ROT*rs to FASTEST_ROT for
+	 * r = rc to rs, with rs being half the canvas diagonal.
+	 *
+	 * The values are picked such that we achieve sufficient precision at
+	 * a reasonably large distance from the circle (for accidently entering
+	 * the circle would change the mode) but can also spin quickly, e.g.,
+	 * when a 180 degrees rotation is needed.
+	 *
+	 * First, normalize to 0 ... 1
+	 * Then, we start at exp(0) and end at
+	 * exp(ln(SLOWEST_ROT*rs/FASTEST_ROT)))
+	 */
+	rs = hypot(sx(s), sy(s))/2;
+	rot = (r-rc)/(rs-rc);
+	rot = SLOWEST_ROT*rs*exp(-rot*log(SLOWEST_ROT*rs/FASTEST_ROT));
+
 	switch (event->direction) {
 	case GDK_SCROLL_UP:
 		if (center)
 			shift(&s->a->m, dx, dy, 1);
 		else
-			rotate(&s->a->m, dx > 0 ? r : -r);
+			rotate(&s->a->m, dx > 0 ? rot : -rot);
 		draw_image(darea, s, osd);
 		break;
 	case GDK_SCROLL_DOWN:
 		if (center)
 			shift(&s->a->m, dx, dy, -1);
 		else
-			rotate(&s->a->m, dx > 0 ? -r : r);
+			rotate(&s->a->m, dx > 0 ? -rot : rot);
 		draw_image(darea, s, osd);
 		break;
 	default:
diff --git a/solidify/style.h b/solidify/style.h
index 14bb978..e678b15 100644
--- a/solidify/style.h
+++ b/solidify/style.h
@@ -23,6 +23,8 @@ extern GdkGC *gc_osd;
 #define	LEVEL_CENTER_DIV	5	/* fraction of diagonal */
 #define	OVERLAP_BORDER		10	/* pixels around min. drawing area */
 #define	OVERLAP_CENTER_DIV	5	/* fraction of diagonal */
+#define	SLOWEST_ROT		3	/* thrice the half-diagonal */
+#define	FASTEST_ROT		2	/* one pixel in distance of 2 pixels */
 
 
 void init_style(GdkDrawable *da);