💚

spec/lines-yardstick-spec.coffee

@@ -40,6 +40,7 @@ describe "LinesYardstick", ->
     mockLineNodesProvider.setFontForScopes(
       ["source.js", "storage.modifier.js"], "16px monospace"
     )
+    linesYardstick.clearCache()
 
     conversionTable = [
       [[0, 0], {left: 0, top: editor.getLineHeightInPixels() * 0}]
@@ -56,3 +57,19 @@ describe "LinesYardstick", ->
       expect(
         linesYardstick.pixelPositionForScreenPosition(point)
       ).toEqual(position)
+
+  it "does not compute the same position twice unless the cache gets cleared", ->
+    mockLineNodesProvider.setDefaultFont("14px monospace")
+
+    oldPosition1 = linesYardstick.pixelPositionForScreenPosition([0, 5])
+    oldPosition2 = linesYardstick.pixelPositionForScreenPosition([1, 4])
+
+    mockLineNodesProvider.setDefaultFont("16px monospace")
+
+    expect(linesYardstick.pixelPositionForScreenPosition([0, 5])).toEqual(oldPosition1)
+    expect(linesYardstick.pixelPositionForScreenPosition([1, 4])).toEqual(oldPosition2)
+
+    linesYardstick.clearCache()
+
+    expect(linesYardstick.pixelPositionForScreenPosition([0, 5])).not.toEqual(oldPosition1)
+    expect(linesYardstick.pixelPositionForScreenPosition([1, 4])).not.toEqual(oldPosition2)

src/lines-yardstick.coffee

@@ -9,6 +9,9 @@ class LinesYardstick
     @rangeForMeasurement = document.createRange()
     @cachedPositionsByLineId = {}
 
+  clearCache: ->
+    @cachedPositionsByLineId = {}
+
   pixelPositionForScreenPosition: (screenPosition, clip=true) ->
     screenPosition = Point.fromObject(screenPosition)
     screenPosition = @model.clipScreenPosition(screenPosition) if clip

src/text-editor-presenter.coffee

@@ -1046,6 +1046,8 @@ class TextEditorPresenter
     @characterWidthsChanged() unless @batchingCharacterMeasurement
 
   characterWidthsChanged: ->
+    @linesYardstick.clearCache()
+
     @shouldUpdateHorizontalScrollState = true
     @shouldUpdateVerticalScrollState = true
     @shouldUpdateScrollbarsState = true