Add support for WebGL2 RASTERIZER_DISCARD enum.

Add support for the `RASTERIZER_DISCARD` enum for the WebGL2 version
of the `Enable`, `Disable` and `IsEnabled` functions.

See https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.2

components/script/dom/webgl2renderingcontext.rs

@@ -71,6 +71,7 @@ pub struct WebGL2RenderingContext {
     texture_pack_row_length: Cell<usize>,
     texture_pack_skip_pixels: Cell<usize>,
     texture_pack_skip_rows: Cell<usize>,
+    enable_rasterizer_discard: Cell<bool>,
 }
 
 fn typedarray_elem_size(typeid: Type) -> usize {
@@ -124,6 +125,7 @@ impl WebGL2RenderingContext {
             texture_pack_row_length: Cell::new(0),
             texture_pack_skip_pixels: Cell::new(0),
             texture_pack_skip_rows: Cell::new(0),
+            enable_rasterizer_discard: Cell::new(false),
         })
     }
 
@@ -991,12 +993,24 @@ impl WebGL2RenderingContextMethods for WebGL2RenderingContext {
 
     /// https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.3
     fn Enable(&self, cap: u32) {
-        self.base.Enable(cap)
+        match cap {
+            constants::RASTERIZER_DISCARD => {
+                self.enable_rasterizer_discard.set(true);
+                self.base.send_command(WebGLCommand::Enable(cap));
+            },
+            _ => self.base.Enable(cap),
+        }
     }
 
     /// https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.3
     fn Disable(&self, cap: u32) {
-        self.base.Disable(cap)
+        match cap {
+            constants::RASTERIZER_DISCARD => {
+                self.enable_rasterizer_discard.set(false);
+                self.base.send_command(WebGLCommand::Disable(cap));
+            },
+            _ => self.base.Disable(cap),
+        }
     }
 
     /// https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.9
@@ -1200,9 +1214,12 @@ impl WebGL2RenderingContextMethods for WebGL2RenderingContext {
     }
 
     // TODO: We could write this without IPC, recording the calls to `enable` and `disable`.
-    /// https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.3
+    /// https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.2
     fn IsEnabled(&self, cap: u32) -> bool {
-        self.base.IsEnabled(cap)
+        match cap {
+            constants::RASTERIZER_DISCARD => self.enable_rasterizer_discard.get(),
+            _ => self.base.IsEnabled(cap),
+        }
     }
 
     /// https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.6

tests/wpt/webgl/meta/conformance2/transform_feedback/transform_feedback.html.ini

@@ -1,13 +1,4 @@
 [transform_feedback.html]
-  [WebGL test #2: getError expected: NO_ERROR. Was INVALID_ENUM : TRANSFORM_FEEDBACK_BINDING query should succeed]
-    expected: FAIL
-
-  [WebGL test #35: getError expected: NO_ERROR. Was INVALID_ENUM : linking transform feedback shader should not set an error]
-    expected: FAIL
-
-  [WebGL test #29: getError expected: NO_ERROR. Was INVALID_ENUM : linking transform feedback shader should not set an error]
-    expected: FAIL
-
   [WebGL test #31: buffer should match expected values]
     expected: FAIL
 
@@ -26,9 +17,12 @@
   [WebGL test #28: buffer should match expected values]
     expected: FAIL
 
-  [WebGL test #24: getError expected: INVALID_OPERATION. Was INVALID_ENUM : after evaluating: gl.getBufferSubData(gl.TRANSFORM_FEEDBACK_BUFFER, 0, retArray, 0, retArray.length)]
+  [WebGL test #35: getError expected: NO_ERROR. Was INVALID_OPERATION : linking transform feedback shader should not set an error]
     expected: FAIL
 
   [WebGL test #34: TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN query returned an incorrect result 0 (expected 3)]
     expected: FAIL
 
+  [WebGL test #29: getError expected: NO_ERROR. Was INVALID_OPERATION : linking transform feedback shader should not set an error]
+    expected: FAIL
+

tests/wpt/webgl/meta/conformance2/transform_feedback/unwritten-output-defaults-to-zero.html.ini

@@ -1,19 +1,7 @@
 [unwritten-output-defaults-to-zero.html]
-  [WebGL test #1: Fail to set up the program]
-    expected: FAIL
-
-  [WebGL test #2: Fail to set up the program]
-    expected: FAIL
-
-  [WebGL test #1: successfullyParsed should be true (of type boolean). Was undefined (of type undefined).]
-    expected: FAIL
-
-  [WebGL test #2: successfullyParsed should be true (of type boolean). Was undefined (of type undefined).]
-    expected: FAIL
-
   [WebGL test #2: buffer should match expected values]
     expected: FAIL
 
-  [WebGL test #3: getError expected: NO_ERROR. Was INVALID_ENUM : Set up program should succeed]
+  [WebGL test #3: getError expected: NO_ERROR. Was INVALID_OPERATION : Set up program should succeed]
     expected: FAIL