Add viewpoint option

src/doc/en/reference/plot3d/threejs.rst

@@ -59,6 +59,9 @@ Options currently supported by the viewer:
 
 - ``thickness`` -- (default: 1) numeric value for thickness of lines
 
+- ``viewpoint`` -- (default: None) string of the form '[x,y,z],angle' setting the initial viewpoint
+  of the scene; can be determined using the 'Get Viewpoint' option of the information menu
+
 Clicking on the information icon in the lower right-hand corner of the viewer opens
 a menu of available actions. These include saving the three-dimensional scene as a static
 PNG image or as complete HTML source code.

src/sage/ext_data/threejs/threejs_template.html

@@ -146,7 +146,23 @@
 
     var camera = createCamera();
     camera.up.set( 0, 0, 1 );
-    camera.position.set( a[0]*(xMid+xRange), a[1]*(yMid+yRange), a[2]*(zMid+zRange) );
+    camera.position.set( a[0]*xMid, a[1]*yMid, a[2]*zMid );
+
+    var offset = new THREE.Vector3( a[0]*xRange, a[1]*yRange, a[2]*zRange );
+
+    if ( options.viewpoint ) {
+
+        var aa = options.viewpoint.replace('[','').replace(']','').split(',');
+        var axis = new THREE.Vector3( aa[0], aa[1], aa[2] );
+        var angle = aa[3] * Math.PI / 180;
+        var q = new THREE.Quaternion().setFromAxisAngle( axis, angle ).inverse();
+
+        offset.set( 0, 0, offset.length() );
+        offset.applyQuaternion( q );
+
+    }
+
+    camera.position.add( offset );
 
     function createCamera() {
 

src/sage/plot/plot3d/base.pyx

@@ -374,6 +374,7 @@ cdef class Graphics3d(SageObject):
         js_options['decimals'] = options.get('decimals', 2)
         js_options['frame'] = options.get('frame', True)
         js_options['projection'] = options.get('projection', 'perspective')
+        js_options['viewpoint'] = options.get('viewpoint', False)
 
         if js_options['projection'] not in ['perspective', 'orthographic']:
             import warnings