Fix off-screen trace detection

Make the condition test work regardless of the drawing method

Author: lvlte

src/traces/heatmap/plot.js

@@ -136,22 +136,18 @@ module.exports = function(gd, plotinfo, cdheatmaps, heatmapLayer) {
         // setup image nodes
 
         // if image is entirely off-screen, don't even draw it
-        var isOffScreen = (imageWidth <= 0 || imageHeight <= 0);
+        var isOffScreen = (
+            left >= xa._length || right <= 0 || top >= ya._length || bottom <= 0
+        );
 
         if(isOffScreen) {
-            // console.log('isOffScreen', drawingMethod);
-
             var noImage = plotGroup.selectAll('image').data([]);
             noImage.exit().remove();
 
             removeLabels(plotGroup);
             return;
         }
 
-        // console.log('drawingMethod', drawingMethod);
-        // console.log(left, right);
-
-
         // generate image data
 
         var canvasW, canvasH;

test/jasmine/tests/heatmap_test.js

@@ -683,7 +683,7 @@ describe('heatmap plot', function() {
 
             return Plotly.relayout(gd, 'xaxis.range', [2, 3]);
         }).then(function() {
-            assertImageCnt(3);
+            assertImageCnt(2);
 
             return Plotly.relayout(gd, 'xaxis.autorange', true);
         }).then(function() {