Skip invariant for gl_FragCoord on WebGL2 (#2254)

src/back/glsl/mod.rs

@@ -1264,11 +1264,27 @@ impl<'a, W: Write> Writer<'a, W> {
             } => (location, interpolation, sampling),
             crate::Binding::BuiltIn(built_in) => {
                 if let crate::BuiltIn::Position { invariant: true } = built_in {
-                    writeln!(
-                        self.out,
-                        "invariant {};",
-                        glsl_built_in(built_in, output, self.options.version.is_webgl())
-                    )?;
+                    match (self.options.version, self.entry_point.stage) {
+                        (
+                            Version::Embedded {
+                                version: 300,
+                                is_webgl: true,
+                            },
+                            ShaderStage::Fragment,
+                        ) => {
+                            // `invariant gl_FragCoord` is not allowed in WebGL2 and possibly
+                            // OpenGL ES in general (waiting on confirmation).
+                            //
+                            // See https://github.com/KhronosGroup/WebGL/issues/3518
+                        }
+                        _ => {
+                            writeln!(
+                                self.out,
+                                "invariant {};",
+                                glsl_built_in(built_in, output, self.options.version.is_webgl())
+                            )?;
+                        }
+                    }
                 }
                 return Ok(());
             }

tests/in/invariant.param.ron

@@ -0,0 +1,11 @@
+(
+    glsl: (
+        version: Embedded (
+            version: 300,
+            is_webgl: true
+        ),
+        writer_flags: (bits: 0),
+        binding_map: {},
+        zero_initialize_workgroup_memory: true,
+    ),
+)

tests/in/invariant.wgsl

@@ -0,0 +1,7 @@
+@vertex
+fn vs() -> @builtin(position) @invariant vec4<f32> {
+    return vec4<f32>(0.0);
+}
+
+@fragment
+fn fs(@builtin(position) @invariant position: vec4<f32>) { }

tests/out/glsl/invariant.frag_main.Fragment.glsl

@@ -0,0 +1,11 @@
+#version 300 es
+
+precision highp float;
+precision highp int;
+
+
+void main() {
+    vec4 position = gl_FragCoord;
+    return;
+}
+

tests/out/glsl/invariant.fs.Fragment.glsl

@@ -0,0 +1,11 @@
+#version 300 es
+
+precision highp float;
+precision highp int;
+
+
+void main() {
+    vec4 position = gl_FragCoord;
+    return;
+}
+

tests/out/glsl/invariant.vs.Vertex.glsl

@@ -0,0 +1,12 @@
+#version 300 es
+
+precision highp float;
+precision highp int;
+
+invariant gl_Position;
+
+void main() {
+    gl_Position = vec4(0.0);
+    return;
+}
+

tests/snapshots.rs

@@ -558,6 +558,7 @@ fn convert_wgsl() {
         ),
         ("sprite", Targets::SPIRV),
         ("force_point_size_vertex_shader_webgl", Targets::GLSL),
+        ("invariant", Targets::GLSL),
     ];
 
     for &(name, targets) in inputs.iter() {