Auto merge of #16893 - MortimerGoro:webgl_extensions, r=emilio

Implement WebGL extensions

<!-- Please describe your changes on the following line: -->

This PR provides the base for implementing WebGL extensions. It comes with the following ones already implemented and passing all related WebGL conformance tests:

- OES_texture_float
- OES_texture_float_linear
- OES_texture_half_float
- OES_texture_half_float_linear
- OES_vertex_array_object

I'll submit other extensions like compressed textures in a separate PR to ease the review process. I included the 5 extensions in this PR because it's easier to show/review how the WebGL extension base works.

To pass all OES_texture_float_xxx tests I had to add some missing format conversions in WebGLRenderingContext.rs

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/16893)
<!-- Reviewable:end -->

1 files changed, 45 insertions, 0 deletions

diff --git a/components/script/dom/webgl_extensions/ext/oestexturefloatlinear.rs b/components/script/dom/webgl_extensions/ext/oestexturefloatlinear.rs
new file mode 100644
index 00000000000..d9bd061a7f1
--- /dev/null
+++ b/components/script/dom/webgl_extensions/ext/oestexturefloatlinear.rs
@@ -0,0 +1,45 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use dom::bindings::codegen::Bindings::OESTextureFloatLinearBinding;
+use dom::bindings::js::Root;
+use dom::bindings::reflector::{DomObject, Reflector, reflect_dom_object};
+use dom::webglrenderingcontext::WebGLRenderingContext;
+use dom_struct::dom_struct;
+use super::{constants as webgl, WebGLExtension, WebGLExtensions};
+
+#[dom_struct]
+pub struct OESTextureFloatLinear {
+    reflector_: Reflector,
+}
+
+impl OESTextureFloatLinear {
+    fn new_inherited() -> OESTextureFloatLinear {
+        Self {
+            reflector_: Reflector::new(),
+        }
+    }
+}
+
+impl WebGLExtension for OESTextureFloatLinear {
+    type Extension = OESTextureFloatLinear;
+    fn new(ctx: &WebGLRenderingContext) -> Root<OESTextureFloatLinear> {
+        reflect_dom_object(box OESTextureFloatLinear::new_inherited(),
+                           &*ctx.global(),
+                           OESTextureFloatLinearBinding::Wrap)
+    }
+
+    fn is_supported(ext: &WebGLExtensions) -> bool {
+        ext.supports_any_gl_extension(&["GL_OES_texture_float_linear",
+                                        "GL_ARB_texture_float"])
+    }
+
+    fn enable(ext: &WebGLExtensions) {
+        ext.enable_filterable_tex_type(webgl::FLOAT);
+    }
+
+    fn name() -> &'static str {
+        "OES_texture_float_linear"
+    }
+}