From fae507d70d57be7ea3c753f78e506b0a099ede66 Mon Sep 17 00:00:00 2001
From: Antonio Scandurra <as-cii@github.com>
Date: Tue, 20 Sep 2016 15:03:41 +0200
Subject: [PATCH] Don't remeasure the first character of a line

Previously we were ignoring the measurement cache for characters located
at `left: 0px` because `0` is evaluated as falsy in Javascript, causing
those character to be constantly re-measured.

This commit fixes it so that we explicitly check for null values when
consulting the cache.
---
 src/lines-yardstick.coffee | 50 +++++++++++++++++++-------------------
 1 file changed, 25 insertions(+), 25 deletions(-)

diff --git a/src/lines-yardstick.coffee b/src/lines-yardstick.coffee
index 13da96fa1..098fc2288 100644
--- a/src/lines-yardstick.coffee
+++ b/src/lines-yardstick.coffee
@@ -91,34 +91,34 @@ class LinesYardstick
     lineNode = @lineNodesProvider.lineNodeForScreenRow(row)
     lineId = @lineNodesProvider.lineIdForScreenRow(row)
 
-    return 0 unless lineNode?
-
-    if cachedPosition = @leftPixelPositionCache[lineId]?[column]
-      return cachedPosition
-
-    textNodes = @lineNodesProvider.textNodesForScreenRow(row)
-    textNodeStartColumn = 0
-
-    for textNode in textNodes
-      textNodeEndColumn = textNodeStartColumn + textNode.textContent.length
-      if textNodeEndColumn > column
-        indexInTextNode = column - textNodeStartColumn
-        break
+    if lineNode?
+      if @leftPixelPositionCache[lineId]?[column]?
+        @leftPixelPositionCache[lineId][column]
       else
-        textNodeStartColumn = textNodeEndColumn
+        textNodes = @lineNodesProvider.textNodesForScreenRow(row)
+        textNodeStartColumn = 0
+        for textNode in textNodes
+          textNodeEndColumn = textNodeStartColumn + textNode.textContent.length
+          if textNodeEndColumn > column
+            indexInTextNode = column - textNodeStartColumn
+            break
+          else
+            textNodeStartColumn = textNodeEndColumn
 
-    if textNode?
-      indexInTextNode ?= textNode.textContent.length
-      lineOffset = lineNode.getBoundingClientRect().left
-      if indexInTextNode is 0
-        leftPixelPosition = @clientRectForRange(textNode, 0, 1).left
-      else
-        leftPixelPosition = @clientRectForRange(textNode, 0, indexInTextNode).right
-      leftPixelPosition -= lineOffset
+        if textNode?
+          indexInTextNode ?= textNode.textContent.length
+          lineOffset = lineNode.getBoundingClientRect().left
+          if indexInTextNode is 0
+            leftPixelPosition = @clientRectForRange(textNode, 0, 1).left
+          else
+            leftPixelPosition = @clientRectForRange(textNode, 0, indexInTextNode).right
+          leftPixelPosition -= lineOffset
 
-      @leftPixelPositionCache[lineId] ?= {}
-      @leftPixelPositionCache[lineId][column] = leftPixelPosition
-      leftPixelPosition
+          @leftPixelPositionCache[lineId] ?= {}
+          @leftPixelPositionCache[lineId][column] = leftPixelPosition
+          leftPixelPosition
+        else
+          0
     else
       0