third_party/WebKit/LayoutTests/compositing/overlap-map-stack-crash.html

   1 <!DOCTYPE html>
   2 <html>
   3 <head>
   4
   5 <style>
   6 #container {
   7   position: absolute;
   8   z-index: 0;
   9   top: 50px;
  10   left: 50px;
  11   width: 300px;
  12   height: 300px;
  13   background-color: gray;
  14 }
  15
  16 #compositedNegZIndex {
  17   position: absolute;
  18   z-index: -5;
  19   width: 100px;
  20   height: 100px;
  21   background-color: blue;
  22   overflow: scroll;
  23 }
  24
  25 #tall {
  26   height: 1000px;
  27 }
  28
  29 #innocentNegZIndex {
  30   position: absolute;
  31   z-index: -2;
  32   top: 200px;
  33   left: 200px;
  34   width: 100px;
  35   height: 100px;
  36   background-color: lime;
  37 }
  38
  39 #explanation {
  40   position: absolute;
  41   top: 400px;
  42 }
  43 </style>
  44
  45 <script>
  46 if (window.internals) {
  47     window.internals.settings.setPreferCompositingToLCDTextEnabled(true);
  48 }
  49
  50 function doTest() {
  51     if (!window.internals)
  52         document.getElementById("explanation").style.display = "block";
  53
  54     if (window.testRunner)
  55         testRunner.dumpAsText();
  56 }
  57
  58 window.addEventListener("load", doTest, false);
  59 </script>
  60
  61 </head>
  62 <body>
  63
  64 <div id="container">
  65   <div id="compositedNegZIndex">
  66     <div id="tall"></div>
  67   </div>
  68   <div id="innocentNegZIndex"> </div>
  69 </div>
  70
  71 <pre id="explanation" style="display:none;">
  72 Crash after hitting below bottom of overlap stack: https://code.google.com/p/chromium/issues/detail?id=285979
  73
  74 The crashing scenario happened as follows:
  75
  76  - force-compositing-mode is disabled.  As a result, compositing mode is
  77    disabled until a compositing trigger.
  78
  79  - overflow-scroll as the compositing trigger, because it does not enable
  80    compositing mode before computeCompositingRequirements. Other triggers
  81    happen during CompositedLayerMapping incremental update entry points.
  82    (Note: CompositedLayerMapping was formerly known as LayerBacking.)
  83
  84  - The above two requirements are necessary to create the scenario where
  85    the root layer does not create an overlap context.
  86
  87  - The overflow-scroll element has a negative z-index which causes the
  88    parent layer to be composited, too.
  89
  90  - As a result, subsequent children layers need to add themselves to the
  91    overlap map, even if they are not composited.
  92
  93  - The problem, however, is that we never created an overlap context for
  94    these negative z-index non-composited layers. When the layers try to add
  95    themselves to the overlap, they try to access below the bottom of the
  96    stack, and crash.
  97 </pre>
  98
  99 </body>
 100
 101 </html>