[PATCH] Add support for zooming using the scroll-wheel

[Linus Torvalds]

From: Linus Torvalds <torvalds at linux-foundation.org>
Date: Tue, 13 Nov 2012 01:44:16 +0100
Subject: [PATCH] Add support for zooming using the scroll-wheel

This allows zooming in with the scroll-wheel if you have one (or the
two-finger scrolling on a touchpad).

Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
---

This is a nicer way to zoom in/out if you have the required scroll-wheel 
or touchpad. 

The "move around just by moving the mouse" (rather than dragging) may not 
be very traditional, but it works for me. And it means that we share all 
the zoom logic with the "click and hold" zoom model too.

 gtk-gui.c | 41 +++++++++++++++++++++++++++++++++++++----
 1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/gtk-gui.c b/gtk-gui.c
index a2f4a174f66f..3f7b3bf44402 100644
--- a/gtk-gui.c
+++ b/gtk-gui.c
@@ -1340,6 +1340,7 @@ static gboolean profile_tooltip (GtkWidget *widget, gint x, gint y,
 
 }
 
+static double zoom_factor = 1.0;
 static int zoom_x = -1, zoom_y = -1;
 
 static gboolean expose_event(GtkWidget *widget, GdkEventExpose *event, gpointer data)
@@ -1360,9 +1361,10 @@ static gboolean expose_event(GtkWidget *widget, GdkEventExpose *event, gpointer
 	init_profile_background(&gc);
 	cairo_paint(gc.cr);
 
-	if (zoom_x >= 0) {
-		cairo_translate(gc.cr, -1.5*zoom_x, -1.5*zoom_y);
-		cairo_scale(gc.cr, 2.5, 2.5);
+	if (zoom_factor > 1.0) {
+		double n = -(zoom_factor-1);
+		cairo_translate(gc.cr, n*zoom_x, n*zoom_y);
+		cairo_scale(gc.cr, zoom_factor, zoom_factor);
 	}
 
 	if (dive) {
@@ -1378,12 +1380,41 @@ static gboolean expose_event(GtkWidget *widget, GdkEventExpose *event, gpointer
 	return FALSE;
 }
 
+static void zoom_event(int x, int y, double inc)
+{
+	zoom_x = x;
+	zoom_y = y;
+	inc += zoom_factor;
+	if (inc < 1.0)
+		inc = 1.0;
+	else if (inc > 10)
+		inc = 10;
+	zoom_factor = inc;
+}
+
+gboolean scroll_event(GtkWidget *widget, GdkEventScroll *event, gpointer user_data)
+{
+	switch (event->direction) {
+	case GDK_SCROLL_UP:
+		zoom_event(event->x, event->y, 0.1);
+		break;
+	case GDK_SCROLL_DOWN:
+		zoom_event(event->x, event->y, -0.1);
+		break;
+	default:
+		return TRUE;
+	}
+	gtk_widget_queue_draw(widget);
+	return TRUE;
+}
+
 gboolean clicked(GtkWidget *widget, GdkEventButton *event, gpointer user_data)
 {
 	switch (event->button) {
 	case 1:
 		zoom_x = event->x;
 		zoom_y = event->y;
+		zoom_factor = 2.5;
 		break;
 	default:
 		return TRUE;
@@ -1397,6 +1428,7 @@ gboolean released(GtkWidget *widget, GdkEventButton *event, gpointer user_data)
 	switch (event->button) {
 	case 1:
 		zoom_x = zoom_y = -1;
+		zoom_factor = 1.0;
 		break;
 	default:
 		return TRUE;
@@ -1424,9 +1456,10 @@ GtkWidget *dive_profile_widget(void)
 	gtk_widget_set_size_request(da, 350, 250);
 	g_signal_connect(da, "expose_event", G_CALLBACK(expose_event), NULL);
 	g_signal_connect(da, "button-press-event", G_CALLBACK(clicked), NULL);
+	g_signal_connect(da, "scroll-event", G_CALLBACK(scroll_event), NULL);
 	g_signal_connect(da, "button-release-event", G_CALLBACK(released), NULL);
 	g_signal_connect(da, "motion-notify-event", G_CALLBACK(motion), NULL);
-	gtk_widget_add_events(da, GDK_BUTTON_PRESS_MASK | GDK_BUTTON_MOTION_MASK | GDK_BUTTON_RELEASE_MASK);
+	gtk_widget_add_events(da, GDK_BUTTON_PRESS_MASK | GDK_BUTTON_MOTION_MASK | GDK_BUTTON_RELEASE_MASK | GDK_SCROLL_MASK);
 
 	return da;
 }