webgl: Do validation that the framebuffer is complete for FBO operations.

Given that we can't make a complete FBO yet, just return false from
the status check.

components/script/dom/webglframebuffer.rs

@@ -5,6 +5,7 @@
 // https://www.khronos.org/registry/webgl/specs/latest/1.0/webgl.idl
 use canvas_traits::CanvasMsg;
 use dom::bindings::codegen::Bindings::WebGLFramebufferBinding;
+use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::WebGLRenderingContextConstants as constants;
 use dom::bindings::global::GlobalRef;
 use dom::bindings::js::Root;
 use dom::bindings::reflector::reflect_dom_object;
@@ -79,6 +80,12 @@ impl WebGLFramebuffer {
         self.is_deleted.get()
     }
 
+    pub fn check_status(&self) -> u32 {
+        // Until we build support for attaching renderbuffers or
+        // textures, all user FBOs are incomplete.
+        return constants::FRAMEBUFFER_UNSUPPORTED;
+    }
+
     pub fn target(&self) -> Option<u32> {
         self.target.get()
     }

components/script/dom/webglrenderingcontext.rs

@@ -212,6 +212,38 @@ impl WebGLRenderingContext {
         }
     }
 
+    // Helper function for validating framebuffer completeness in
+    // calls touching the framebuffer.  From the GLES 2.0.25 spec,
+    // page 119:
+    //
+    //    "Effects of Framebuffer Completeness on Framebuffer
+    //     Operations
+    //
+    //     If the currently bound framebuffer is not framebuffer
+    //     complete, then it is an error to attempt to use the
+    //     framebuffer for writing or reading. This means that
+    //     rendering commands such as DrawArrays and DrawElements, as
+    //     well as commands that read the framebuffer such as
+    //     ReadPixels and CopyTexSubImage, will generate the error
+    //     INVALID_FRAMEBUFFER_OPERATION if called while the
+    //     framebuffer is not framebuffer complete."
+    //
+    // The WebGL spec mentions a couple more operations that trigger
+    // this: clear() and getParameter(IMPLEMENTATION_COLOR_READ_*).
+    fn validate_framebuffer_complete(&self) -> bool {
+        match self.bound_framebuffer.get() {
+            Some(fb) => match fb.check_status() {
+                constants::FRAMEBUFFER_COMPLETE => return true,
+                _ => {
+                    self.webgl_error(InvalidFramebufferOperation);
+                    return false;
+                }
+            },
+            // The default framebuffer is always complete.
+            None => return true,
+        }
+    }
+
     fn tex_parameter(&self, target: u32, name: u32, value: TexParameterValue) {
         let texture = match target {
             constants::TEXTURE_2D => self.bound_texture_2d.get(),
@@ -886,6 +918,10 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
     // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.8
     fn CopyTexImage2D(&self, target: u32, level: i32, internal_format: u32,
                       x: i32, y: i32, width: i32, height: i32, border: i32) {
+        if !self.validate_framebuffer_complete() {
+            return;
+        }
+
         let validator = CommonTexImage2DValidator::new(self, target, level,
                                                        internal_format, width,
                                                        height, border);
@@ -939,6 +975,10 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
     // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.8
     fn CopyTexSubImage2D(&self, target: u32, level: i32, xoffset: i32, yoffset: i32,
                          x: i32, y: i32, width: i32, height: i32) {
+        if !self.validate_framebuffer_complete() {
+            return;
+        }
+
         // NB: We use a dummy (valid) format and border in order to reuse the
         // common validations, but this should have its own validator.
         let validator = CommonTexImage2DValidator::new(self, target, level,
@@ -978,6 +1018,10 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
 
     // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.11
     fn Clear(&self, mask: u32) {
+        if !self.validate_framebuffer_complete() {
+            return;
+        }
+
         self.ipc_renderer.send(CanvasMsg::WebGL(WebGLCommand::Clear(mask))).unwrap();
         self.mark_as_dirty();
     }
@@ -1204,6 +1248,10 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
                     return self.webgl_error(InvalidValue);
                 }
 
+                if !self.validate_framebuffer_complete() {
+                    return;
+                }
+
                 self.ipc_renderer
                     .send(CanvasMsg::WebGL(WebGLCommand::DrawArrays(mode, first, count)))
                     .unwrap();
@@ -1240,6 +1288,10 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
             return self.webgl_error(InvalidOperation);
         }
 
+        if !self.validate_framebuffer_complete() {
+            return;
+        }
+
         match mode {
             constants::POINTS | constants::LINE_STRIP |
             constants::LINE_LOOP | constants::LINES |
@@ -1508,6 +1560,10 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
             None => return self.webgl_error(InvalidValue),
         };
 
+        if !self.validate_framebuffer_complete() {
+            return;
+        }
+
         match unsafe { JS_GetArrayBufferViewType(pixels) } {
             Type::Uint8 => (),
             _ => return self.webgl_error(InvalidOperation)