66832 2011-08-23 18:06:01 -0700 LayoutTests/canvas/philip/tests/2d.path.stroke.prune.arc.html misinterprets pruning requirement 2011-08-29 11:20:53 -0700 1 1 1 Unclassified WebKit Tools / Tests 528+ (Nightly build) Unspecified Unspecified RESOLVED FIXED P2 Normal --- 55696 1 tomz tomz kling oldest_to_newest 455897 0 104950 tomz 2011-08-23 18:06:01 -0700 Created attachment 104950 Demo of path pruning when arc length = 0 WebKit incorrectly prunes the path when it contains a 0 length arc, and the 2d.path.stroke.prune.arc test is expecting/enforcing that behavior. In addition to removing the 0 length arc, we are also removing the connecting line. From the spec, at http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#complex-shapes-%28paths%29 <quote> context.arc(x,y,radius,startAngle,endAngle[,anticlockwise]) adds points to the subpath such that the arc described by the arguments .../snip/... is added to the path, connected to the previous point by a straight line. : : : The arc(x, y, radius, startAngle, endAngle, anticlockwise) method draws an arc. If the context has any subpaths, then the method must add a straight line from the last point in the subpath to the start point of the arc. In any case, it must draw the arc between the start point of the arc and the end point of the arc, and add the start and end points of the arc to the subpath. The arc and its start and end points are defined as follows: : : : If the two points are the same, or if the radius is zero, then the arc is defined as being of zero length in both directions. : : : And then under general path stuff... "Zero-length line segments must be pruned before stroking a path. Empty subpaths must be ignored." </quote> Now consider the case of several arc calls. If you follow all of the steps and construct paths you construct a series of arcs with connecting lines. If we set one arc length to 0, the current interpretation (enforced by this test) has us removing the non-zero length connecting line also. That goes beyond what the spec says, and differs from the interpretation of all other tested browsers, including: IE, Firefox, and Opera. See the attached example. Problems with the current interpretation include: * Divergence from *all* other browser engines, * Divergence from how svg handles analogous paths * Divergence from WebKit's own handling of 0 length line segments created by lineTo. * Violates principle of least surprise. Behavior at arcLen == 0 differs (discontinuously) from behavior as arcLen approaches 0. We can fix the WebKit behavior under https://bugs.webkit.org/show_bug.cgi?id=55696, but this test will start failing. 456306 1 105042 tomz 2011-08-24 12:28:16 -0700 Created attachment 105042 Demo of path pruning compared to path when arc is not pruned 458309 2 tomz 2011-08-29 11:20:53 -0700 Fixed by patch for https://bugs.webkit.org/show_bug.cgi?id=55696. 104950 2011-08-23 18:06:01 -0700 2011-08-23 18:06:01 -0700 Demo of path pruning when arc length = 0 prune-arc-demo.html text/html 416 tomz PGh0bWw+Cjxib2R5PgogICA8Y2FudmFzIGlkPSJjdnMiIHdpZHRoPSI2MDAiIGhlaWdodD0iNjAw IiBzdHlsZT0iYm9yZGVyOiAxcHggZGFzaGVkIGJsYWNrIj5bTm8gY2FudmFzIHN1cHBvcnRdPC9j YW52YXM+CiAgIDxzY3JpcHQ+CiAgICAgICBjbyA9IGRvY3VtZW50LmdldEVsZW1lbnRCeUlkKCJj dnMiKS5nZXRDb250ZXh0KCcyZCcpOwogICAgICAgY28uYmVnaW5QYXRoKCk7CiAgICAgICAgICAg Y28uYXJjKDEwMCwxMDAsMzAsMC43NSwzLjc1LDApOwogICAgICAgICAgIGNvLmFyYygzMDAsMjAw LDMwLDAuNzUsMC43NSwwKTsgICAvLyB6ZXJvIGFyYy1sZW5ndGgKICAgICAgICAgICBjby5hcmMo NTAwLDEwMCwzMCwwLjc1LDMuNzUsMCk7CiAgICAgICBjby5zdHJva2UoKTsKICA8L3NjcmlwdD4K PC9ib2R5Lz4KPC9odG1sPgo= 105042 2011-08-24 12:28:16 -0700 2011-08-24 12:28:16 -0700 Demo of path pruning compared to path when arc is not pruned prune-arc-compare.html text/html 610 tomz PGh0bWw+Cjxib2R5PgogICA8Y2FudmFzIGlkPSJjdnMiIHdpZHRoPSI2MDAiIGhlaWdodD0iNjAw IiBzdHlsZT0iYm9yZGVyOiAxcHggZGFzaGVkIGJsYWNrIj5bTm8gY2FudmFzIHN1cHBvcnRdPC9j YW52YXM+CiAgIDxzY3JpcHQ+CiAgICAgICBjbyA9IGRvY3VtZW50LmdldEVsZW1lbnRCeUlkKCJj dnMiKS5nZXRDb250ZXh0KCcyZCcpOwogICAgICAgY28uYmVnaW5QYXRoKCk7CiAgICAgICAgICAg Y28uYXJjKDEwMCwxMDAsMzAsMC43NSwzLjc1LDApOwogICAgICAgICAgIGNvLmFyYygzMDAsMjAw LDMwLDAuNzUsMC43NSwwKTsgICAvLyB6ZXJvIGFyYy1sZW5ndGgKICAgICAgICAgICBjby5hcmMo NTAwLDEwMCwzMCwwLjc1LDMuNzUsMCk7CiAgICAgICBjby5zdHJva2UoKTsKICAgICAgIGNvLmJl Z2luUGF0aCgpOwogICAgICAgICAgIGNvLmFyYygxMDAsNDAwLDMwLDAuNzUsMy43NSwwKTsKICAg ICAgICAgICBjby5hcmMoMzAwLDUwMCwzMCwwLjc1LDMuNzUsMCk7ICAgLy8gemVybyBhcmMtbGVu Z3RoCiAgICAgICAgICAgY28uYXJjKDUwMCw0MDAsMzAsMC43NSwzLjc1LDApOwogICAgICAgY28u c3Ryb2tlKCk7CiAgIDwvc2NyaXB0Pgo8L2JvZHkvPgo8L2h0bWw+Cg==