altoslib: Add set_zoom_centre to AltosMap

This zooms around a specific point, keeping it at the same place on
the screen.

Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/altoslib/AltosMap.java b/altoslib/AltosMap.java
index 59420d4b..adf52ab9 100644
--- a/altoslib/AltosMap.java
+++ b/altoslib/AltosMap.java
@@ -166,6 +166,7 @@ public class AltosMap implements AltosMapTileListener, AltosMapStoreListener {
 
 
 	public boolean set_zoom(int zoom) {
+		notice_user_input();
 		if (AltosMap.min_zoom <= zoom && zoom <= AltosMap.max_zoom && zoom != this.zoom) {
 			this.zoom = zoom;
 			tiles.clear();
@@ -176,6 +177,29 @@ public class AltosMap implements AltosMapTileListener, AltosMapStoreListener {
 		return false;
 	}
 
+	public boolean set_zoom_centre(int zoom, AltosPointInt centre) {
+		AltosLatLon	mouse_lat_lon = null;
+		boolean		ret;
+
+		if (transform != null)
+			mouse_lat_lon = transform.screen_lat_lon(centre);
+
+		ret = set_zoom(zoom);
+
+		if (ret && mouse_lat_lon != null) {
+			AltosPointDouble	new_mouse = transform.screen(mouse_lat_lon);
+
+			double	dx = width()/2.0 - centre.x;
+			double	dy = height()/2.0 - centre.y;
+
+			AltosLatLon	new_centre = transform.screen_lat_lon(new AltosPointDouble(new_mouse.x + dx, new_mouse.y + dy));
+
+			centre(new_centre);
+		}
+
+		return ret;
+	}
+
 	public int get_zoom() {
 		return zoom;
 	}