Auto merge of #16544 - MortimerGoro:get_shader_precision_format, r=jdm

Implement WebGL::GetShaderPrecisionFormat

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Implement WebGL::GetShaderPrecisionFormat. See https://github.com/servo/gleam/pull/119 && https://github.com/servo/webrender/pull/1127

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #13985 (github issue number if applicable).

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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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components/script/dom/webglrenderingcontext.rs

@@ -31,6 +31,7 @@ use dom::webglframebuffer::WebGLFramebuffer;
 use dom::webglprogram::WebGLProgram;
 use dom::webglrenderbuffer::WebGLRenderbuffer;
 use dom::webglshader::WebGLShader;
+use dom::webglshaderprecisionformat::WebGLShaderPrecisionFormat;
 use dom::webgltexture::{TexParameterValue, WebGLTexture};
 use dom::webgluniformlocation::WebGLUniformLocation;
 use dom::window::Window;
@@ -1902,6 +1903,27 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
         }
     }
 
+    // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.9
+    fn GetShaderPrecisionFormat(&self,
+                                shader_type: u32,
+                                precision_type: u32)
+                                -> Option<Root<WebGLShaderPrecisionFormat>> {
+        let (sender, receiver) = webrender_traits::channel::msg_channel().unwrap();
+        self.ipc_renderer.send(CanvasMsg::WebGL(WebGLCommand::GetShaderPrecisionFormat(shader_type,
+                                                                                       precision_type,
+                                                                                       sender)))
+                                                                                       .unwrap();
+        match receiver.recv().unwrap() {
+            Ok((range_min, range_max, precision)) => {
+                Some(WebGLShaderPrecisionFormat::new(self.global().as_window(), range_min, range_max, precision))
+            },
+            Err(error) => {
+                self.webgl_error(error);
+                None
+            }
+        }
+    }
+
     // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.10
     fn GetUniformLocation(&self,
                           program: Option<&WebGLProgram>,

components/script/dom/webglshader.rs

@@ -106,9 +106,11 @@ impl WebGLShader {
         }
 
         if let Some(ref source) = *self.source.borrow() {
+            let mut params = BuiltInResources::default();
+            params.FragmentPrecisionHigh = 1;
             let validator = ShaderValidator::for_webgl(self.gl_type,
                                                        SHADER_OUTPUT_FORMAT,
-                                                       &BuiltInResources::default()).unwrap();
+                                                       &params).unwrap();
             match validator.compile_and_translate(&[source]) {
                 Ok(translated_source) => {
                     debug!("Shader translated: {}", translated_source);

components/script/dom/webidls/WebGLRenderingContext.webidl

@@ -595,7 +595,7 @@ interface WebGLRenderingContextBase
     DOMString? getProgramInfoLog(WebGLProgram? program);
     //any getRenderbufferParameter(GLenum target, GLenum pname);
     any getShaderParameter(WebGLShader? shader, GLenum pname);
-    //WebGLShaderPrecisionFormat? getShaderPrecisionFormat(GLenum shadertype, GLenum precisiontype);
+    WebGLShaderPrecisionFormat? getShaderPrecisionFormat(GLenum shadertype, GLenum precisiontype);
     DOMString? getShaderInfoLog(WebGLShader? shader);
 
     DOMString? getShaderSource(WebGLShader? shader);