canvasfeature labels do not stay visible

[nicgirault]

With CanvasFeature track, labels are not visible when a feature is larger than the screen whereas with the HTMLFeature track, labels have a behavior similar to the css position property with value "fixed".

[rbuels]

This was almost fixed in #219, but only the arrowheads got done.

[cmdcolin]

Basic idea for this can be accomplished like this

diff --git a/src/JBrowse/View/FeatureGlyph/Box.js b/src/JBrowse/View/FeatureGlyph/Box.js
index a390244..ddcc6ec 100644
--- a/src/JBrowse/View/FeatureGlyph/Box.js
+++ b/src/JBrowse/View/FeatureGlyph/Box.js
@@ -327,8 +327,30 @@ return declare([ FeatureGlyph, FeatureLabelMixin ], {
         var fDescriptionWidth = fRect.description ? fRect.description.w : 0;
         var maxLeft = bpToPx( fMax ) - Math.max(fLabelWidth, fDescriptionWidth) - bpToPx( vMin );
         var minLeft = bpToPx( fMin ) - bpToPx( vMin );
-
+        if( fRect.label ) {
+            if( fMin <= vMin) {
+                context.font = fRect.label.font;
+                context.fillStyle = fRect.label.fill;
+                context.textBaseline = fRect.label.baseline;
+                context.fillText( fRect.label.text,
+                                  0,
+                                  fRect.t+(fRect.label.yOffset||0)
+                                );
+            }
+        }
+        if( fRect.description ) {
+            if( fMin <= vMin) {
+                context.font = fRect.description.font;
+                context.fillStyle = fRect.description.fill;
+                context.textBaseline = fRect.description.baseline;
+                context.fillText(
+                    fRect.description.text,
+                    0,
+                    fRect.t + (fRect.description.yOffset||0)
+                );
+            }
+        }

See http://gmod.827538.n3.nabble.com/Gmod-ajax-Labels-on-really-long-features-td4051495.html

[cmdcolin]

Example

This demonstrates two things

a) doesn't take the track label into account (html features moves feature label to the right to make room for track label)

b) doesn't try and remove subfeature label. some question of whether this is ok or not

[rbuels]

@cmdcolin feel like putting that patch into a pull request?? :-))))