From 2560ce1acb0ecb910cc8f9045b0019f04cbf63d8 Mon Sep 17 00:00:00 2001
From: Alon Levy <alon@pobox.com>
Date: Mon, 6 Apr 2015 17:50:54 +0300
Subject: client: return zoom buttons, make zoom conserve center point

---
 src/client/buttons.js         | 34 ++++++++++++++++++++++++++++++++++
 src/client/view/graph_view.js | 10 ++++++++--
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/src/client/buttons.js b/src/client/buttons.js
index 8a0b6b7d..00554c8b 100644
--- a/src/client/buttons.js
+++ b/src/client/buttons.js
@@ -214,5 +214,39 @@ $('#btn_rzdoc__open').click(function() {
     cmd_bar.fadeToggle(400);
 });
 
+function log_scale(max_in, min_out, max_out) {
+    var t = (min_out * max_out - 1) / (min_out + max_out - 2),
+        k = 1 / max_in * Math.log((max_out - t) / (1 - t));
+
+    return function (x) { return (1 - t) * Math.exp(x * k) + t; };
+}
+
+function exp_scale(max_in, min_out, max_out) {
+    var t = (min_out * max_out - 1) / (min_out + max_out - 2),
+        k = 1 / max_in * Math.log((max_out - t) / (1 - t));
+
+    return function (y) { return (1 / k) * Math.log((y - t) / (1 - t)); };
+}
+
+function clip(min, max, v) {
+    return Math.max(min, Math.min(max, v));
+}
+
+var zoom_range = 10,
+    zoom_min = 0.1,
+    zoom_max = 3,
+    zoom_exp_to_linear = exp_scale(zoom_range, zoom_min, zoom_max);
+
+$('#btn_zoom_in').asEventStream('click')
+    .map(1)
+    .merge($('#btn_zoom_out').asEventStream('click').map(-1))
+    .map(function (change) {
+        return clip(-zoom_range, zoom_range, zoom_exp_to_linear(rz_core.main_graph_view.zoom_obj.scale()) + change);
+    })
+    .map(log_scale(zoom_range, zoom_min, zoom_max))
+    .onValue(function (val) {
+        rz_core.main_graph_view.scale__absolute(val);
+    });
+
 return {'buttons': 'nothing here'};
 }); // define
diff --git a/src/client/view/graph_view.js b/src/client/view/graph_view.js
index 9bafc620..f6be8ebf 100644
--- a/src/client/view/graph_view.js
+++ b/src/client/view/graph_view.js
@@ -828,8 +828,14 @@ function GraphView(spec) {
     }
     gv.__set_scale_translate = set_scale_translate;
 
-    var scale__absolute = function (scale) {
-        set_scale_translate(scale, zoom_obj.translate());
+    var scale__absolute = function (new_scale) {
+        var t = zoom_obj.translate(),
+            s = zoom_obj.scale(),
+            ds = new_scale - s,
+            w = window.innerWidth,
+            h = window.innerHeight;
+
+        set_scale_translate(new_scale, [t[0] - ds * w / 2, t[1] - ds * h / 2]);
     }
 
     gv.scale__absolute = scale__absolute;
-- 
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