Fix panic when perspective property is zero.

servo · Jan 28, 2016 · 183c3f5 · 183c3f5
1 parent 34954a9
commit 183c3f5
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Showing 4 changed files with 104 additions and 2 deletions.
diff --git a/components/layout/display_list_builder.rs b/components/layout/display_list_builder.rs
@@ -63,6 +63,23 @@ use util::range::Range;
 /// The logical width of an insertion point: at the moment, a one-pixel-wide line.
 const INSERTION_POINT_LOGICAL_WIDTH: Au = Au(1 * AU_PER_PX);
 
+// TODO(gw): The transforms spec says that perspective length must
+// be positive. However, there is some confusion between the spec
+// and browser implementations as to handling the case of 0 for the
+// perspective value. Until the spec bug is resolved, at least ensure
+// that a provided perspective value of <= 0.0 doesn't cause panics
+// and behaves as it does in other browsers.
+// See https://lists.w3.org/Archives/Public/www-style/2016Jan/0020.html for more details.
+#[inline]
+fn create_perspective_matrix(d: Au) -> Matrix4 {
+    let d = d.to_f32_px();
+    if d <= 0.0 {
+        Matrix4::identity()
+    } else {
+        Matrix4::create_perspective(d)
+    }
+}
+
 pub trait FragmentDisplayListBuilding {
     /// Adds the display items necessary to paint the background of this fragment to the display
     /// list if necessary.
@@ -1241,7 +1258,7 @@ impl FragmentDisplayListBuilding for Fragment {
                         Matrix4::create_rotation(ax, ay, az, theta)
                     }
                     transform::ComputedOperation::Perspective(d) => {
-                        Matrix4::create_perspective(d.to_f32_px())
+                        create_perspective_matrix(d)
                     }
                     transform::ComputedOperation::Scale(sx, sy, sz) => {
                         Matrix4::create_scale(sx, sy, sz)
@@ -1282,7 +1299,7 @@ impl FragmentDisplayListBuilding for Fragment {
                                                                  -perspective_origin.y,
                                                                  0.0);
 
-                let perspective_matrix = Matrix4::create_perspective(d.to_f32_px());
+                let perspective_matrix = create_perspective_matrix(d);
 
                 pre_transform.mul(&perspective_matrix).mul(&post_transform)
             }

diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -3536,6 +3536,18 @@
             "url": "/_mozilla/css/percentage_width_inline_block_a.html"
           }
         ],
+        "css/perspective_zero.html": [
+          {
+            "path": "css/perspective_zero.html",
+            "references": [
+              [
+                "/_mozilla/css/perspective_zero_ref.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/css/perspective_zero.html"
+          }
+        ],
         "css/pixel_snapping_border_a.html": [
           {
             "dpi": "2",
@@ -9616,6 +9628,18 @@
           "url": "/_mozilla/css/percentage_width_inline_block_a.html"
         }
       ],
+      "css/perspective_zero.html": [
+        {
+          "path": "css/perspective_zero.html",
+          "references": [
+            [
+              "/_mozilla/css/perspective_zero_ref.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/css/perspective_zero.html"
+        }
+      ],
       "css/pixel_snapping_border_a.html": [
         {
           "dpi": "2",

diff --git a/tests/wpt/mozilla/tests/css/perspective_zero.html b/tests/wpt/mozilla/tests/css/perspective_zero.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <link rel='match' href='perspective_zero_ref.html'>
+        <style type="text/css">
+            html, body {
+                margin: 0;
+            }
+
+            #outer {
+                perspective: 0px;
+                transform-style: preserve-3d;
+            }
+
+            #inner {
+                position: absolute;
+                top: 100px;
+                left: 100px;
+                width: 100px;
+                height: 100px;
+                background-color: green;
+                transform: translate3d(0, 0, 0);
+            }
+        </style>
+    </head>
+    <body>
+        <div id="outer">
+            <div id="inner"></div>
+        </div>
+    </body>
+</html>
diff --git a/tests/wpt/mozilla/tests/css/perspective_zero_ref.html b/tests/wpt/mozilla/tests/css/perspective_zero_ref.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <style type="text/css">
+            html, body {
+                margin: 0;
+            }
+
+            #outer {
+                perspective: 10px;
+                transform-style: preserve-3d;
+            }
+
+            #inner {
+                position: absolute;
+                top: 100px;
+                left: 100px;
+                width: 100px;
+                height: 100px;
+                background-color: green;
+                transform: translate3d(0, 0, 0);
+            }
+        </style>
+    </head>
+    <body>
+        <div id="outer">
+            <div id="inner"></div>
+        </div>
+    </body>
+</html>