From 4866be1f522eb56c93fbbcb705da6a864097f588 Mon Sep 17 00:00:00 2001
From: "Anthony J. Thibault" <tony@highfidelity.io>
Date: Tue, 21 Feb 2017 16:01:46 -0800
Subject: [PATCH] More consistent tablet angle when first creating the tablet.

The tablet should more constantly be placed above your hand, while facing your head.
It fixes the issue where the tablet would appear almost horizontal when your hand was close to your HMD and at eye level.
---
 scripts/system/libraries/WebTablet.js | 28 ++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/scripts/system/libraries/WebTablet.js b/scripts/system/libraries/WebTablet.js
index 74bbd788be..618b70ff20 100644
--- a/scripts/system/libraries/WebTablet.js
+++ b/scripts/system/libraries/WebTablet.js
@@ -49,24 +49,30 @@ function calcSpawnInfo(hand, height) {
         var handController = getControllerWorldLocation(hand, true);
         var controllerPosition = handController.position;
 
-        // compute the angle of the chord with length (height / 2)
-        var theta = Math.asin(height / (2 * Vec3.distance(headPos, controllerPosition)));
+        // base of the tablet is slightly above controller position
+        var TABLET_BASE_DISPLACEMENT = {x: 0, y: 0.1, z: 0};
+        var tabletBase = Vec3.sum(controllerPosition, TABLET_BASE_DISPLACEMENT);
 
-        // then we can use this angle to rotate the vector between the HMD position and the center of the tablet.
-        // this vector, u, will become our new look at direction.
-        var d = Vec3.normalize(Vec3.subtract(headPos, controllerPosition));
+        var d = Vec3.subtract(headPos, tabletBase);
+        var theta = Math.acos(d.y / Vec3.length(d));
+        d.y = 0;
+        if (Vec3.length(d) < 0.0001) {
+            d = {x: 1, y: 0, z: 0};
+        } else {
+            d = Vec3.normalize(d);
+        }
         var w = Vec3.normalize(Vec3.cross(Y_AXIS, d));
-        var q = Quat.angleAxis(theta * (180 / Math.PI), w);
+        var ANGLE_OFFSET = 25;
+        var q = Quat.angleAxis(theta * (180 / Math.PI) - (90 - ANGLE_OFFSET), w);
         var u = Vec3.multiplyQbyV(q, d);
 
         // use u to compute a full lookAt quaternion.
-        var lookAtRot = Quat.lookAt(controllerPosition, Vec3.sum(controllerPosition, u), Y_AXIS);
-
-        // adjust the tablet position by a small amount.
-        var yDisplacement = (height / 2) + 0.1;
+        var lookAtRot = Quat.lookAt(tabletBase, Vec3.sum(tabletBase, u), Y_AXIS);
+        var yDisplacement = (height / 2);
         var zDisplacement = 0.05;
         var tabletOffset = Vec3.multiplyQbyV(lookAtRot, {x: 0, y: yDisplacement, z: zDisplacement});
-        finalPosition = Vec3.sum(controllerPosition, tabletOffset);
+        finalPosition = Vec3.sum(tabletBase, tabletOffset);
+
         return {
             position: finalPosition,
             rotation: lookAtRot