Auto merge of #20317 - gootorov:webgl-getFramebufferAttachmentParameter, r=jdm

Implement WebGL getFrameBufferAttachmentParameter API

<!-- Please describe your changes on the following line: -->
Implementation of `getFramebufferAttachmentParameter` as in WebGL1 specification.

Part of https://github.com/servo/servo/issues/10209.

r? emilio or jdm.

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

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- [x] There are tests for these changes

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4 files changed, 132 insertions, 3 deletions

diff --git a/components/script/dom/webgl2renderingcontext.rs b/components/script/dom/webgl2renderingcontext.rs
index 2a25c450b08..2d1186c0dcc 100644
--- a/components/script/dom/webgl2renderingcontext.rs
+++ b/components/script/dom/webgl2renderingcontext.rs
@@ -142,6 +142,18 @@ impl WebGL2RenderingContextMethods for WebGL2RenderingContext {
         self.base.GetExtension(cx, name)
     }
 
+    #[allow(unsafe_code)]
+    /// https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.4
+    unsafe fn GetFramebufferAttachmentParameter(
+        &self,
+        cx: *mut JSContext,
+        target: u32,
+        attachment: u32,
+        pname: u32
+    ) -> JSVal {
+        self.base.GetFramebufferAttachmentParameter(cx, target, attachment, pname)
+    }
+
     /// https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.3
     fn ActiveTexture(&self, texture: u32) {
         self.base.ActiveTexture(texture)
diff --git a/components/script/dom/webglframebuffer.rs b/components/script/dom/webglframebuffer.rs
index c9165609cdb..ccea1efec7b 100644
--- a/components/script/dom/webglframebuffer.rs
+++ b/components/script/dom/webglframebuffer.rs
@@ -25,6 +25,12 @@ enum WebGLFramebufferAttachment {
     Texture { texture: Dom<WebGLTexture>, level: i32 },
 }
 
+#[derive(Clone, JSTraceable, MallocSizeOf)]
+pub enum WebGLFramebufferAttachmentRoot {
+    Renderbuffer(DomRoot<WebGLRenderbuffer>),
+    Texture(DomRoot<WebGLTexture>),
+}
+
 #[dom_struct]
 pub struct WebGLFramebuffer {
     webgl_object: WebGLObject,
@@ -213,6 +219,25 @@ impl WebGLFramebuffer {
         Ok(())
     }
 
+    pub fn attachment(&self, attachment: u32) -> Option<WebGLFramebufferAttachmentRoot> {
+        let binding = match attachment {
+            constants::COLOR_ATTACHMENT0 => &self.color,
+            constants::DEPTH_ATTACHMENT => &self.depth,
+            constants::STENCIL_ATTACHMENT => &self.stencil,
+            constants::DEPTH_STENCIL_ATTACHMENT => &self.depthstencil,
+            _ => return None,
+        };
+
+        binding.borrow().as_ref().map(|bin| {
+            match bin {
+                &WebGLFramebufferAttachment::Renderbuffer(ref rb) =>
+                    WebGLFramebufferAttachmentRoot::Renderbuffer(DomRoot::from_ref(&rb)),
+                &WebGLFramebufferAttachment::Texture { ref texture, .. } =>
+                    WebGLFramebufferAttachmentRoot::Texture(DomRoot::from_ref(&texture)),
+            }
+        })
+    }
+
     pub fn texture2d(&self, attachment: u32, textarget: u32, texture: Option<&WebGLTexture>,
                      level: i32) -> WebGLResult<()> {
         let binding = match attachment {
diff --git a/components/script/dom/webglrenderingcontext.rs b/components/script/dom/webglrenderingcontext.rs
index 64990da1504..ad572751607 100644
--- a/components/script/dom/webglrenderingcontext.rs
+++ b/components/script/dom/webglrenderingcontext.rs
@@ -10,6 +10,7 @@ use canvas_traits::webgl::DOMToTextureCommand;
 use canvas_traits::webgl::WebGLError::*;
 use canvas_traits::webgl::webgl_channel;
 use dom::bindings::cell::DomRefCell;
+use dom::bindings::codegen::Bindings::WebGL2RenderingContextBinding::WebGL2RenderingContextConstants as WebGL2Constants;
 use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::{self, WebGLContextAttributes};
 use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::WebGLRenderingContextConstants as constants;
 use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::WebGLRenderingContextMethods;
@@ -33,7 +34,7 @@ use dom::webgl_validations::types::{TexDataType, TexFormat, TexImageTarget};
 use dom::webglactiveinfo::WebGLActiveInfo;
 use dom::webglbuffer::WebGLBuffer;
 use dom::webglcontextevent::WebGLContextEvent;
-use dom::webglframebuffer::WebGLFramebuffer;
+use dom::webglframebuffer::{WebGLFramebuffer, WebGLFramebufferAttachmentRoot};
 use dom::webglprogram::WebGLProgram;
 use dom::webglrenderbuffer::WebGLRenderbuffer;
 use dom::webglshader::WebGLShader;
@@ -1554,6 +1555,10 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
 
     // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.6
     fn BindFramebuffer(&self, target: u32, framebuffer: Option<&WebGLFramebuffer>) {
+        if target == WebGL2Constants::READ_FRAMEBUFFER {
+            return self.webgl_error(InvalidEnum);
+        }
+
         if target != constants::FRAMEBUFFER {
             return self.webgl_error(InvalidOperation);
         }
@@ -2297,6 +2302,93 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
         }
     }
 
+    #[allow(unsafe_code)]
+    // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.6
+    unsafe fn GetFramebufferAttachmentParameter(
+        &self,
+        cx: *mut JSContext,
+        target: u32,
+        attachment: u32,
+        pname: u32
+    ) -> JSVal {
+        // Check if currently bound framebuffer is non-zero as per spec.
+        if self.bound_framebuffer.get().is_none() {
+            self.webgl_error(InvalidOperation);
+            return NullValue();
+        }
+
+        // Note: commented out stuff is for the WebGL2 standard.
+        let target_matches = match target {
+            // constants::READ_FRAMEBUFFER |
+            // constants::DRAW_FRAMEBUFFER => true,
+            constants::FRAMEBUFFER => true,
+            _ => false
+        };
+        let attachment_matches = match attachment {
+            // constants::MAX_COLOR_ATTACHMENTS ... gl::COLOR_ATTACHMENT0 |
+            // constants::BACK |
+            constants::COLOR_ATTACHMENT0 |
+            constants::DEPTH_STENCIL_ATTACHMENT |
+            constants::DEPTH_ATTACHMENT |
+            constants::STENCIL_ATTACHMENT => true,
+            _ => false,
+        };
+        let pname_matches = match pname {
+            // constants::FRAMEBUFFER_ATTACHMENT_ALPHA_SIZE |
+            // constants::FRAMEBUFFER_ATTACHMENT_BLUE_SIZE |
+            // constants::FRAMEBUFFER_ATTACHMENT_COLOR_ENCODING |
+            // constants::FRAMEBUFFER_ATTACHMENT_COMPONENT_TYPE |
+            // constants::FRAMEBUFFER_ATTACHMENT_DEPTH_SIZE |
+            // constants::FRAMEBUFFER_ATTACHMENT_GREEN_SIZE |
+            // constants::FRAMEBUFFER_ATTACHMENT_RED_SIZE |
+            // constants::FRAMEBUFFER_ATTACHMENT_STENCIL_SIZE |
+            // constants::FRAMEBUFFER_ATTACHMENT_TEXTURE_LAYER |
+            constants::FRAMEBUFFER_ATTACHMENT_OBJECT_NAME |
+            constants::FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE |
+            constants::FRAMEBUFFER_ATTACHMENT_TEXTURE_CUBE_MAP_FACE |
+            constants::FRAMEBUFFER_ATTACHMENT_TEXTURE_LEVEL => true,
+            _ => false
+        };
+
+        if !target_matches || !attachment_matches || !pname_matches {
+            self.webgl_error(InvalidEnum);
+            return NullValue();
+        }
+
+        // From the GLES2 spec:
+        //
+        //     If the value of FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE is NONE,
+        //     then querying any other pname will generate INVALID_ENUM.
+        //
+        // otherwise, return `WebGLRenderbuffer` or `WebGLTexture` dom object
+        if pname == constants::FRAMEBUFFER_ATTACHMENT_OBJECT_NAME {
+            // if fb is None, an INVALID_OPERATION is returned
+            // at the beggining of the function, so `.unwrap()` will never panic
+            let fb = self.bound_framebuffer.get().unwrap();
+            if let Some(webgl_attachment) = fb.attachment(attachment) {
+                match webgl_attachment {
+                    WebGLFramebufferAttachmentRoot::Renderbuffer(rb) => {
+                        rooted!(in(cx) let mut rval = NullValue());
+                        rb.to_jsval(cx, rval.handle_mut());
+                        return rval.get();
+                    },
+                    WebGLFramebufferAttachmentRoot::Texture(texture) => {
+                        rooted!(in(cx) let mut rval = NullValue());
+                        texture.to_jsval(cx, rval.handle_mut());
+                        return rval.get();
+                    },
+                }
+            }
+            self.webgl_error(InvalidEnum);
+            return NullValue();
+        }
+
+        let (sender, receiver) = webgl_channel().unwrap();
+        self.send_command(WebGLCommand::GetFramebufferAttachmentParameter(target, attachment, pname, sender));
+
+        Int32Value(receiver.recv().unwrap())
+    }
+
     // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.9
     fn GetProgramInfoLog(&self, program: Option<&WebGLProgram>) -> Option<DOMString> {
         if let Some(program) = program {
diff --git a/components/script/dom/webidls/WebGLRenderingContext.webidl b/components/script/dom/webidls/WebGLRenderingContext.webidl
index 3f845126701..05e9212d974 100644
--- a/components/script/dom/webidls/WebGLRenderingContext.webidl
+++ b/components/script/dom/webidls/WebGLRenderingContext.webidl
@@ -589,8 +589,8 @@ interface WebGLRenderingContextBase
 
     [WebGLHandlesContextLoss] GLenum getError();
 
-    //any getFramebufferAttachmentParameter(GLenum target, GLenum attachment,
-    //                                      GLenum pname);
+    any getFramebufferAttachmentParameter(GLenum target, GLenum attachment,
+                                          GLenum pname);
     any getProgramParameter(WebGLProgram? program, GLenum pname);
     DOMString? getProgramInfoLog(WebGLProgram? program);
     //any getRenderbufferParameter(GLenum target, GLenum pname);