This CL implements the first draft of Canvas 2D Context Attributes, aka getContext('2d', { alpha: f…

LayoutTests/fast/canvas/alpha.js

+description("Series of tests for canvas alpha");
+
+var canvas1 = document.getElementById("canvas1");
+var canvas2 = document.getElementById("canvas2");
+var canvas3 = document.getElementById("canvas3");
+var canvas4 = document.getElementById("canvas4");
+
+var ctx1 = canvas1.getContext("2d");
+var ctx2 = canvas2.getContext("2d", {} );
+var ctx3 = canvas3.getContext("2d", { alpha: false } );
+var ctx4 = canvas4.getContext("2d", { alpha: true } );
+
+shouldBe("ctx1.getContextAttributes().alpha", "true");
+var imgData1 = ctx1.getImageData(0, 0, 1, 1);
+shouldBe("imgData1.data[0]", "0");
+shouldBe("imgData1.data[1]", "0");
+shouldBe("imgData1.data[2]", "0");
+shouldBe("imgData1.data[3]", "0");
+
+shouldBe("ctx2.getContextAttributes().alpha", "true");
+var imgData2 = ctx2.getImageData(0, 0, 1, 1);
+shouldBe("imgData2.data[0]", "0");
+shouldBe("imgData2.data[1]", "0");
+shouldBe("imgData2.data[2]", "0");
+shouldBe("imgData2.data[3]", "0");
+
+shouldBe("ctx3.getContextAttributes().alpha", "false");
+var imgData3 = ctx3.getImageData(0, 0, 1, 1);
+shouldBe("imgData3.data[0]", "0");
+shouldBe("imgData3.data[1]", "0");
+shouldBe("imgData3.data[2]", "0");
+shouldBe("imgData3.data[3]", "255");
+
+shouldBe("ctx4.getContextAttributes().alpha", "true");
+var imgData4 = ctx4.getImageData(0, 0, 1, 1);
+shouldBe("imgData4.data[0]", "0");
+shouldBe("imgData4.data[1]", "0");
+shouldBe("imgData4.data[2]", "0");
+shouldBe("imgData4.data[3]", "0");
+
+// Check that mutating the returned value of getContextAttributes() doesn't
+// affect the existing canvas, or the values of subsequent calls to
+// getContextAttributes().
+var attrs = ctx4.getContextAttributes();
+shouldBe("attrs.alpha", "true");
+attrs.alpha = false;
+var imgData4 = ctx4.getImageData(0, 0, 1, 1);
+shouldBe("ctx4.getContextAttributes().alpha", "true");
+shouldBe("imgData4.data[0]", "0");
+shouldBe("imgData4.data[1]", "0");
+shouldBe("imgData4.data[2]", "0");
+shouldBe("imgData4.data[3]", "0");