Add m-esr52 at 52.6.0

1 files changed, 1322 insertions, 0 deletions

diff --git a/devtools/server/actors/webgl.js b/devtools/server/actors/webgl.js
new file mode 100644
index 000000000..137448647
--- /dev/null
+++ b/devtools/server/actors/webgl.js
@@ -0,0 +1,1322 @@
+/* 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 strict";
+
+const {Cc, Ci, Cu, Cr} = require("chrome");
+const events = require("sdk/event/core");
+const promise = require("promise");
+const protocol = require("devtools/shared/protocol");
+const { ContentObserver } = require("devtools/shared/content-observer");
+const { on, once, off, emit } = events;
+const { method, Arg, Option, RetVal } = protocol;
+const {
+  shaderSpec,
+  programSpec,
+  webGLSpec,
+} = require("devtools/shared/specs/webgl");
+
+const WEBGL_CONTEXT_NAMES = ["webgl", "experimental-webgl", "moz-webgl"];
+
+// These traits are bit masks. Make sure they're powers of 2.
+const PROGRAM_DEFAULT_TRAITS = 0;
+const PROGRAM_BLACKBOX_TRAIT = 1;
+const PROGRAM_HIGHLIGHT_TRAIT = 2;
+
+/**
+ * A WebGL Shader contributing to building a WebGL Program.
+ * You can either retrieve, or compile the source of a shader, which will
+ * automatically inflict the necessary changes to the WebGL state.
+ */
+var ShaderActor = protocol.ActorClassWithSpec(shaderSpec, {
+  /**
+   * Create the shader actor.
+   *
+   * @param DebuggerServerConnection conn
+   *        The server connection.
+   * @param WebGLProgram program
+   *        The WebGL program being linked.
+   * @param WebGLShader shader
+   *        The cooresponding vertex or fragment shader.
+   * @param WebGLProxy proxy
+   *        The proxy methods for the WebGL context owning this shader.
+   */
+  initialize: function (conn, program, shader, proxy) {
+    protocol.Actor.prototype.initialize.call(this, conn);
+    this.program = program;
+    this.shader = shader;
+    this.text = proxy.getShaderSource(shader);
+    this.linkedProxy = proxy;
+  },
+
+  /**
+   * Gets the source code for this shader.
+   */
+  getText: function () {
+    return this.text;
+  },
+
+  /**
+   * Sets and compiles new source code for this shader.
+   */
+  compile: function (text) {
+    // Get the shader and corresponding program to change via the WebGL proxy.
+    let { linkedProxy: proxy, shader, program } = this;
+
+    // Get the new shader source to inject.
+    let oldText = this.text;
+    let newText = text;
+
+    // Overwrite the shader's source.
+    let error = proxy.compileShader(program, shader, this.text = newText);
+
+    // If something went wrong, revert to the previous shader.
+    if (error.compile || error.link) {
+      proxy.compileShader(program, shader, this.text = oldText);
+      return error;
+    }
+    return undefined;
+  }
+});
+
+/**
+ * A WebGL program is composed (at the moment, analogue to OpenGL ES 2.0)
+ * of two shaders: a vertex shader and a fragment shader.
+ */
+var ProgramActor = protocol.ActorClassWithSpec(programSpec, {
+  /**
+   * Create the program actor.
+   *
+   * @param DebuggerServerConnection conn
+   *        The server connection.
+   * @param WebGLProgram program
+   *        The WebGL program being linked.
+   * @param WebGLShader[] shaders
+   *        The WebGL program's cooresponding vertex and fragment shaders.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context owning this program.
+   * @param WebGLProxy proxy
+   *        The proxy methods for the WebGL context owning this program.
+   */
+  initialize: function (conn, [program, shaders, cache, proxy]) {
+    protocol.Actor.prototype.initialize.call(this, conn);
+    this._shaderActorsCache = { vertex: null, fragment: null };
+    this.program = program;
+    this.shaders = shaders;
+    this.linkedCache = cache;
+    this.linkedProxy = proxy;
+  },
+
+  get ownerWindow() {
+    return this.linkedCache.ownerWindow;
+  },
+
+  get ownerContext() {
+    return this.linkedCache.ownerContext;
+  },
+
+  /**
+   * Gets the vertex shader linked to this program. This method guarantees
+   * a single actor instance per shader.
+   */
+  getVertexShader: function () {
+    return this._getShaderActor("vertex");
+  },
+
+  /**
+   * Gets the fragment shader linked to this program. This method guarantees
+   * a single actor instance per shader.
+   */
+  getFragmentShader: function () {
+    return this._getShaderActor("fragment");
+  },
+
+  /**
+   * Highlights any geometry rendered using this program.
+   */
+  highlight: function (tint) {
+    this.linkedProxy.highlightTint = tint;
+    this.linkedCache.setProgramTrait(this.program, PROGRAM_HIGHLIGHT_TRAIT);
+  },
+
+  /**
+   * Allows geometry to be rendered normally using this program.
+   */
+  unhighlight: function () {
+    this.linkedCache.unsetProgramTrait(this.program, PROGRAM_HIGHLIGHT_TRAIT);
+  },
+
+  /**
+   * Prevents any geometry from being rendered using this program.
+   */
+  blackbox: function () {
+    this.linkedCache.setProgramTrait(this.program, PROGRAM_BLACKBOX_TRAIT);
+  },
+
+  /**
+   * Allows geometry to be rendered using this program.
+   */
+  unblackbox: function () {
+    this.linkedCache.unsetProgramTrait(this.program, PROGRAM_BLACKBOX_TRAIT);
+  },
+
+  /**
+   * Returns a cached ShaderActor instance based on the required shader type.
+   *
+   * @param string type
+   *        Either "vertex" or "fragment".
+   * @return ShaderActor
+   *         The respective shader actor instance.
+   */
+  _getShaderActor: function (type) {
+    if (this._shaderActorsCache[type]) {
+      return this._shaderActorsCache[type];
+    }
+    let proxy = this.linkedProxy;
+    let shader = proxy.getShaderOfType(this.shaders, type);
+    let shaderActor = new ShaderActor(this.conn, this.program, shader, proxy);
+    return this._shaderActorsCache[type] = shaderActor;
+  }
+});
+
+/**
+ * The WebGL Actor handles simple interaction with a WebGL context via a few
+ * high-level methods. After instantiating this actor, you'll need to set it
+ * up by calling setup().
+ */
+var WebGLActor = exports.WebGLActor = protocol.ActorClassWithSpec(webGLSpec, {
+  initialize: function (conn, tabActor) {
+    protocol.Actor.prototype.initialize.call(this, conn);
+    this.tabActor = tabActor;
+    this._onGlobalCreated = this._onGlobalCreated.bind(this);
+    this._onGlobalDestroyed = this._onGlobalDestroyed.bind(this);
+    this._onProgramLinked = this._onProgramLinked.bind(this);
+  },
+  destroy: function (conn) {
+    protocol.Actor.prototype.destroy.call(this, conn);
+    this.finalize();
+  },
+
+  /**
+   * Starts waiting for the current tab actor's document global to be
+   * created, in order to instrument the Canvas context and become
+   * aware of everything the content does WebGL-wise.
+   *
+   * See ContentObserver and WebGLInstrumenter for more details.
+   */
+  setup: function ({ reload }) {
+    if (this._initialized) {
+      return;
+    }
+    this._initialized = true;
+
+    this._programActorsCache = [];
+    this._webglObserver = new WebGLObserver();
+
+    on(this.tabActor, "window-ready", this._onGlobalCreated);
+    on(this.tabActor, "window-destroyed", this._onGlobalDestroyed);
+    on(this._webglObserver, "program-linked", this._onProgramLinked);
+
+    if (reload) {
+      this.tabActor.window.location.reload();
+    }
+  },
+
+  /**
+   * Stops listening for document global changes and puts this actor
+   * to hibernation. This method is called automatically just before the
+   * actor is destroyed.
+   */
+  finalize: function () {
+    if (!this._initialized) {
+      return;
+    }
+    this._initialized = false;
+
+    off(this.tabActor, "window-ready", this._onGlobalCreated);
+    off(this.tabActor, "window-destroyed", this._onGlobalDestroyed);
+    off(this._webglObserver, "program-linked", this._onProgramLinked);
+
+    this._programActorsCache = null;
+    this._contentObserver = null;
+    this._webglObserver = null;
+  },
+
+  /**
+   * Gets an array of cached program actors for the current tab actor's window.
+   * This is useful for dealing with bfcache, when no new programs are linked.
+   */
+  getPrograms: function () {
+    let id = ContentObserver.GetInnerWindowID(this.tabActor.window);
+    return this._programActorsCache.filter(e => e.ownerWindow == id);
+  },
+
+  /**
+   * Waits for one frame via `requestAnimationFrame` on the tab actor's window.
+   * Used in tests.
+   */
+  waitForFrame: function () {
+    let deferred = promise.defer();
+    this.tabActor.window.requestAnimationFrame(deferred.resolve);
+    return deferred.promise;
+  },
+
+  /**
+   * Gets a pixel's RGBA value from a context specified by selector
+   * and the coordinates of the pixel in question.
+   * Currently only used in tests.
+   *
+   * @param string selector
+   *        A string selector to select the canvas in question from the DOM.
+   * @param Object position
+   *        An object with an `x` and `y` property indicating coordinates of the pixel being inspected.
+   * @return Object
+   *        An object containing `r`, `g`, `b`, and `a` properties of the pixel.
+   */
+  getPixel: function ({ selector, position }) {
+    let { x, y } = position;
+    let canvas = this.tabActor.window.document.querySelector(selector);
+    let context = XPCNativeWrapper.unwrap(canvas.getContext("webgl"));
+    let { proxy } = this._webglObserver.for(context);
+    let height = canvas.height;
+
+    let buffer = new this.tabActor.window.Uint8Array(4);
+    buffer = XPCNativeWrapper.unwrap(buffer);
+
+    proxy.readPixels(x, height - y - 1, 1, 1, context.RGBA, context.UNSIGNED_BYTE, buffer);
+
+    return { r: buffer[0], g: buffer[1], b: buffer[2], a: buffer[3] };
+  },
+
+  /**
+   * Gets an array of all cached program actors belonging to all windows.
+   * This should only be used for tests.
+   */
+  _getAllPrograms: function () {
+    return this._programActorsCache;
+  },
+
+
+  /**
+   * Invoked whenever the current tab actor's document global is created.
+   */
+  _onGlobalCreated: function ({id, window, isTopLevel}) {
+    if (isTopLevel) {
+      WebGLInstrumenter.handle(window, this._webglObserver);
+      events.emit(this, "global-created", id);
+    }
+  },
+
+  /**
+   * Invoked whenever the current tab actor's inner window is destroyed.
+   */
+  _onGlobalDestroyed: function ({id, isTopLevel, isFrozen}) {
+    if (isTopLevel && !isFrozen) {
+      removeFromArray(this._programActorsCache, e => e.ownerWindow == id);
+      this._webglObserver.unregisterContextsForWindow(id);
+      events.emit(this, "global-destroyed", id);
+    }
+  },
+
+  /**
+   * Invoked whenever an observed WebGL context links a program.
+   */
+  _onProgramLinked: function (...args) {
+    let programActor = new ProgramActor(this.conn, args);
+    this._programActorsCache.push(programActor);
+    events.emit(this, "program-linked", programActor);
+  }
+});
+
+/**
+ * Instruments a HTMLCanvasElement with the appropriate inspection methods.
+ */
+var WebGLInstrumenter = {
+  /**
+   * Overrides the getContext method in the HTMLCanvasElement prototype.
+   *
+   * @param nsIDOMWindow window
+   *        The window to perform the instrumentation in.
+   * @param WebGLObserver observer
+   *        The observer watching function calls in the context.
+   */
+  handle: function (window, observer) {
+    let self = this;
+
+    let id = ContentObserver.GetInnerWindowID(window);
+    let canvasElem = XPCNativeWrapper.unwrap(window.HTMLCanvasElement);
+    let canvasPrototype = canvasElem.prototype;
+    let originalGetContext = canvasPrototype.getContext;
+
+    /**
+     * Returns a drawing context on the canvas, or null if the context ID is
+     * not supported. This override creates an observer for the targeted context
+     * type and instruments specific functions in the targeted context instance.
+     */
+    canvasPrototype.getContext = function (name, options) {
+      // Make sure a context was able to be created.
+      let context = originalGetContext.call(this, name, options);
+      if (!context) {
+        return context;
+      }
+      // Make sure a WebGL (not a 2D) context will be instrumented.
+      if (WEBGL_CONTEXT_NAMES.indexOf(name) == -1) {
+        return context;
+      }
+      // Repeated calls to 'getContext' return the same instance, no need to
+      // instrument everything again.
+      if (observer.for(context)) {
+        return context;
+      }
+
+      // Create a separate state storage for this context.
+      observer.registerContextForWindow(id, context);
+
+      // Link our observer to the new WebGL context methods.
+      for (let { timing, callback, functions } of self._methods) {
+        for (let func of functions) {
+          self._instrument(observer, context, func, callback, timing);
+        }
+      }
+
+      // Return the decorated context back to the content consumer, which
+      // will continue using it normally.
+      return context;
+    };
+  },
+
+  /**
+   * Overrides a specific method in a HTMLCanvasElement context.
+   *
+   * @param WebGLObserver observer
+   *        The observer watching function calls in the context.
+   * @param WebGLRenderingContext context
+   *        The targeted WebGL context instance.
+   * @param string funcName
+   *        The function to override.
+   * @param array callbackName [optional]
+   *        The two callback function names in the observer, corresponding to
+   *        the "before" and "after" invocation times. If unspecified, they will
+   *        default to the name of the function to override.
+   * @param number timing [optional]
+   *        When to issue the callback in relation to the actual context
+   *        function call. Availalble values are -1 for "before" (default)
+   *        1 for "after" and 0 for "before and after".
+   */
+  _instrument: function (observer, context, funcName, callbackName = [], timing = -1) {
+    let { cache, proxy } = observer.for(context);
+    let originalFunc = context[funcName];
+    let beforeFuncName = callbackName[0] || funcName;
+    let afterFuncName = callbackName[1] || callbackName[0] || funcName;
+
+    context[funcName] = function (...glArgs) {
+      if (timing <= 0 && !observer.suppressHandlers) {
+        let glBreak = observer[beforeFuncName](glArgs, cache, proxy);
+        if (glBreak) return undefined;
+      }
+
+      // Invoking .apply on an unxrayed content function doesn't work, because
+      // the arguments array is inaccessible to it. Get Xrays back.
+      let glResult = Cu.waiveXrays(Cu.unwaiveXrays(originalFunc).apply(this, glArgs));
+
+      if (timing >= 0 && !observer.suppressHandlers) {
+        let glBreak = observer[afterFuncName](glArgs, glResult, cache, proxy);
+        if (glBreak) return undefined;
+      }
+
+      return glResult;
+    };
+  },
+
+  /**
+   * Override mappings for WebGL methods.
+   */
+  _methods: [{
+    timing: 1, // after
+    functions: [
+      "linkProgram", "getAttribLocation", "getUniformLocation"
+    ]
+  }, {
+    timing: -1, // before
+    callback: [
+      "toggleVertexAttribArray"
+    ],
+    functions: [
+      "enableVertexAttribArray", "disableVertexAttribArray"
+    ]
+  }, {
+    timing: -1, // before
+    callback: [
+      "attribute_"
+    ],
+    functions: [
+      "vertexAttrib1f", "vertexAttrib2f", "vertexAttrib3f", "vertexAttrib4f",
+      "vertexAttrib1fv", "vertexAttrib2fv", "vertexAttrib3fv", "vertexAttrib4fv",
+      "vertexAttribPointer"
+    ]
+  }, {
+    timing: -1, // before
+    callback: [
+      "uniform_"
+    ],
+    functions: [
+      "uniform1i", "uniform2i", "uniform3i", "uniform4i",
+      "uniform1f", "uniform2f", "uniform3f", "uniform4f",
+      "uniform1iv", "uniform2iv", "uniform3iv", "uniform4iv",
+      "uniform1fv", "uniform2fv", "uniform3fv", "uniform4fv",
+      "uniformMatrix2fv", "uniformMatrix3fv", "uniformMatrix4fv"
+    ]
+  }, {
+    timing: -1, // before
+    functions: [
+      "useProgram", "enable", "disable", "blendColor",
+      "blendEquation", "blendEquationSeparate",
+      "blendFunc", "blendFuncSeparate"
+    ]
+  }, {
+    timing: 0, // before and after
+    callback: [
+      "beforeDraw_", "afterDraw_"
+    ],
+    functions: [
+      "drawArrays", "drawElements"
+    ]
+  }]
+  // TODO: It'd be a good idea to handle other functions as well:
+  //   - getActiveUniform
+  //   - getUniform
+  //   - getActiveAttrib
+  //   - getVertexAttrib
+};
+
+/**
+ * An observer that captures a WebGL context's method calls.
+ */
+function WebGLObserver() {
+  this._contexts = new Map();
+}
+
+WebGLObserver.prototype = {
+  _contexts: null,
+
+  /**
+   * Creates a WebGLCache and a WebGLProxy for the specified window and context.
+   *
+   * @param number id
+   *        The id of the window containing the WebGL context.
+   * @param WebGLRenderingContext context
+   *        The WebGL context used in the cache and proxy instances.
+   */
+  registerContextForWindow: function (id, context) {
+    let cache = new WebGLCache(id, context);
+    let proxy = new WebGLProxy(id, context, cache, this);
+    cache.refreshState(proxy);
+
+    this._contexts.set(context, {
+      ownerWindow: id,
+      cache: cache,
+      proxy: proxy
+    });
+  },
+
+  /**
+   * Removes all WebGLCache and WebGLProxy instances for a particular window.
+   *
+   * @param number id
+   *        The id of the window containing the WebGL context.
+   */
+  unregisterContextsForWindow: function (id) {
+    removeFromMap(this._contexts, e => e.ownerWindow == id);
+  },
+
+  /**
+   * Gets the WebGLCache and WebGLProxy instances for a particular context.
+   *
+   * @param WebGLRenderingContext context
+   *        The WebGL context used in the cache and proxy instances.
+   * @return object
+   *         An object containing the corresponding { cache, proxy } instances.
+   */
+  for: function (context) {
+    return this._contexts.get(context);
+  },
+
+  /**
+   * Set this flag to true to stop observing any context function calls.
+   */
+  suppressHandlers: false,
+
+  /**
+   * Called immediately *after* 'linkProgram' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param void glResult
+   *        The returned value of the original function call.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   * @param WebGLProxy proxy
+   *        The proxy methods for the WebGL context initiating this call.
+   */
+  linkProgram: function (glArgs, glResult, cache, proxy) {
+    let program = glArgs[0];
+    let shaders = proxy.getAttachedShaders(program);
+    cache.addProgram(program, PROGRAM_DEFAULT_TRAITS);
+    emit(this, "program-linked", program, shaders, cache, proxy);
+  },
+
+  /**
+   * Called immediately *after* 'getAttribLocation' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param GLint glResult
+   *        The returned value of the original function call.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  getAttribLocation: function (glArgs, glResult, cache) {
+    // Make sure the attribute's value is legal before caching.
+    if (glResult < 0) {
+      return;
+    }
+    let [program, name] = glArgs;
+    cache.addAttribute(program, name, glResult);
+  },
+
+  /**
+   * Called immediately *after* 'getUniformLocation' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLUniformLocation glResult
+   *        The returned value of the original function call.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  getUniformLocation: function (glArgs, glResult, cache) {
+    // Make sure the uniform's value is legal before caching.
+    if (!glResult) {
+      return;
+    }
+    let [program, name] = glArgs;
+    cache.addUniform(program, name, glResult);
+  },
+
+  /**
+   * Called immediately *before* 'enableVertexAttribArray' or
+   * 'disableVertexAttribArray'is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  toggleVertexAttribArray: function (glArgs, cache) {
+    glArgs[0] = cache.getCurrentAttributeLocation(glArgs[0]);
+    return glArgs[0] < 0; // Return true to break original function call.
+  },
+
+  /**
+   * Called immediately *before* 'attribute_' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  attribute_: function (glArgs, cache) {
+    glArgs[0] = cache.getCurrentAttributeLocation(glArgs[0]);
+    return glArgs[0] < 0; // Return true to break original function call.
+  },
+
+  /**
+   * Called immediately *before* 'uniform_' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  uniform_: function (glArgs, cache) {
+    glArgs[0] = cache.getCurrentUniformLocation(glArgs[0]);
+    return !glArgs[0]; // Return true to break original function call.
+  },
+
+  /**
+   * Called immediately *before* 'useProgram' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  useProgram: function (glArgs, cache) {
+    // Manually keeping a cache and not using gl.getParameter(CURRENT_PROGRAM)
+    // because gl.get* functions are slow as potatoes.
+    cache.currentProgram = glArgs[0];
+  },
+
+  /**
+   * Called immediately *before* 'enable' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  enable: function (glArgs, cache) {
+    cache.currentState[glArgs[0]] = true;
+  },
+
+  /**
+   * Called immediately *before* 'disable' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  disable: function (glArgs, cache) {
+    cache.currentState[glArgs[0]] = false;
+  },
+
+  /**
+   * Called immediately *before* 'blendColor' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  blendColor: function (glArgs, cache) {
+    let blendColor = cache.currentState.blendColor;
+    blendColor[0] = glArgs[0];
+    blendColor[1] = glArgs[1];
+    blendColor[2] = glArgs[2];
+    blendColor[3] = glArgs[3];
+  },
+
+  /**
+   * Called immediately *before* 'blendEquation' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  blendEquation: function (glArgs, cache) {
+    let state = cache.currentState;
+    state.blendEquationRgb = state.blendEquationAlpha = glArgs[0];
+  },
+
+  /**
+   * Called immediately *before* 'blendEquationSeparate' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  blendEquationSeparate: function (glArgs, cache) {
+    let state = cache.currentState;
+    state.blendEquationRgb = glArgs[0];
+    state.blendEquationAlpha = glArgs[1];
+  },
+
+  /**
+   * Called immediately *before* 'blendFunc' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  blendFunc: function (glArgs, cache) {
+    let state = cache.currentState;
+    state.blendSrcRgb = state.blendSrcAlpha = glArgs[0];
+    state.blendDstRgb = state.blendDstAlpha = glArgs[1];
+  },
+
+  /**
+   * Called immediately *before* 'blendFuncSeparate' is requested in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   */
+  blendFuncSeparate: function (glArgs, cache) {
+    let state = cache.currentState;
+    state.blendSrcRgb = glArgs[0];
+    state.blendDstRgb = glArgs[1];
+    state.blendSrcAlpha = glArgs[2];
+    state.blendDstAlpha = glArgs[3];
+  },
+
+  /**
+   * Called immediately *before* 'drawArrays' or 'drawElements' is requested
+   * in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   * @param WebGLProxy proxy
+   *        The proxy methods for the WebGL context initiating this call.
+   */
+  beforeDraw_: function (glArgs, cache, proxy) {
+    let traits = cache.currentProgramTraits;
+
+    // Handle program blackboxing.
+    if (traits & PROGRAM_BLACKBOX_TRAIT) {
+      return true; // Return true to break original function call.
+    }
+    // Handle program highlighting.
+    if (traits & PROGRAM_HIGHLIGHT_TRAIT) {
+      proxy.enableHighlighting();
+    }
+
+    return false;
+  },
+
+  /**
+   * Called immediately *after* 'drawArrays' or 'drawElements' is requested
+   * in the context.
+   *
+   * @param array glArgs
+   *        Overridable arguments with which the function is called.
+   * @param void glResult
+   *        The returned value of the original function call.
+   * @param WebGLCache cache
+   *        The state storage for the WebGL context initiating this call.
+   * @param WebGLProxy proxy
+   *        The proxy methods for the WebGL context initiating this call.
+   */
+  afterDraw_: function (glArgs, glResult, cache, proxy) {
+    let traits = cache.currentProgramTraits;
+
+    // Handle program highlighting.
+    if (traits & PROGRAM_HIGHLIGHT_TRAIT) {
+      proxy.disableHighlighting();
+    }
+  }
+};
+
+/**
+ * A mechanism for storing a single WebGL context's state, programs, shaders,
+ * attributes or uniforms.
+ *
+ * @param number id
+ *        The id of the window containing the WebGL context.
+ * @param WebGLRenderingContext context
+ *        The WebGL context for which the state is stored.
+ */
+function WebGLCache(id, context) {
+  this._id = id;
+  this._gl = context;
+  this._programs = new Map();
+  this.currentState = {};
+}
+
+WebGLCache.prototype = {
+  _id: 0,
+  _gl: null,
+  _programs: null,
+  _currentProgramInfo: null,
+  _currentAttributesMap: null,
+  _currentUniformsMap: null,
+
+  get ownerWindow() {
+    return this._id;
+  },
+
+  get ownerContext() {
+    return this._gl;
+  },
+
+  /**
+   * A collection of flags or properties representing the context's state.
+   * Implemented as an object hash and not a Map instance because keys are
+   * always either strings or numbers.
+   */
+  currentState: null,
+
+  /**
+   * Populates the current state with values retrieved from the context.
+   *
+   * @param WebGLProxy proxy
+   *        The proxy methods for the WebGL context owning the state.
+   */
+  refreshState: function (proxy) {
+    let gl = this._gl;
+    let s = this.currentState;
+
+    // Populate only with the necessary parameters. Not all default WebGL
+    // state values are required.
+    s[gl.BLEND] = proxy.isEnabled("BLEND");
+    s.blendColor = proxy.getParameter("BLEND_COLOR");
+    s.blendEquationRgb = proxy.getParameter("BLEND_EQUATION_RGB");
+    s.blendEquationAlpha = proxy.getParameter("BLEND_EQUATION_ALPHA");
+    s.blendSrcRgb = proxy.getParameter("BLEND_SRC_RGB");
+    s.blendSrcAlpha = proxy.getParameter("BLEND_SRC_ALPHA");
+    s.blendDstRgb = proxy.getParameter("BLEND_DST_RGB");
+    s.blendDstAlpha = proxy.getParameter("BLEND_DST_ALPHA");
+  },
+
+  /**
+   * Adds a program to the cache.
+   *
+   * @param WebGLProgram program
+   *        The shader for which the traits are to be cached.
+   * @param number traits
+   *        A default properties mask set for the program.
+   */
+  addProgram: function (program, traits) {
+    this._programs.set(program, {
+      traits: traits,
+      attributes: [], // keys are GLints (numbers)
+      uniforms: new Map() // keys are WebGLUniformLocations (objects)
+    });
+  },
+
+  /**
+   * Adds a specific trait to a program. The effect of such properties is
+   * determined by the consumer of this cache.
+   *
+   * @param WebGLProgram program
+   *        The program to add the trait to.
+   * @param number trait
+   *        The property added to the program.
+   */
+  setProgramTrait: function (program, trait) {
+    this._programs.get(program).traits |= trait;
+  },
+
+  /**
+   * Removes a specific trait from a program.
+   *
+   * @param WebGLProgram program
+   *        The program to remove the trait from.
+   * @param number trait
+   *        The property removed from the program.
+   */
+  unsetProgramTrait: function (program, trait) {
+    this._programs.get(program).traits &= ~trait;
+  },
+
+  /**
+   * Sets the currently used program in the context.
+   * @param WebGLProgram program
+   */
+  set currentProgram(program) {
+    let programInfo = this._programs.get(program);
+    if (programInfo == null) {
+      return;
+    }
+    this._currentProgramInfo = programInfo;
+    this._currentAttributesMap = programInfo.attributes;
+    this._currentUniformsMap = programInfo.uniforms;
+  },
+
+  /**
+   * Gets the traits for the currently used program.
+   * @return number
+   */
+  get currentProgramTraits() {
+    return this._currentProgramInfo.traits;
+  },
+
+  /**
+   * Adds an attribute to the cache.
+   *
+   * @param WebGLProgram program
+   *        The program for which the attribute is bound.
+   * @param string name
+   *        The attribute name.
+   * @param GLint value
+   *        The attribute value.
+   */
+  addAttribute: function (program, name, value) {
+    this._programs.get(program).attributes[value] = {
+      name: name,
+      value: value
+    };
+  },
+
+  /**
+   * Adds a uniform to the cache.
+   *
+   * @param WebGLProgram program
+   *        The program for which the uniform is bound.
+   * @param string name
+   *        The uniform name.
+   * @param WebGLUniformLocation value
+   *        The uniform value.
+   */
+  addUniform: function (program, name, value) {
+    this._programs.get(program).uniforms.set(new XPCNativeWrapper(value), {
+      name: name,
+      value: value
+    });
+  },
+
+  /**
+   * Updates the attribute locations for a specific program.
+   * This is necessary, for example, when the shader is relinked and all the
+   * attribute locations become obsolete.
+   *
+   * @param WebGLProgram program
+   *        The program for which the attributes need updating.
+   */
+  updateAttributesForProgram: function (program) {
+    let attributes = this._programs.get(program).attributes;
+    for (let attribute of attributes) {
+      attribute.value = this._gl.getAttribLocation(program, attribute.name);
+    }
+  },
+
+  /**
+   * Updates the uniform locations for a specific program.
+   * This is necessary, for example, when the shader is relinked and all the
+   * uniform locations become obsolete.
+   *
+   * @param WebGLProgram program
+   *        The program for which the uniforms need updating.
+   */
+  updateUniformsForProgram: function (program) {
+    let uniforms = this._programs.get(program).uniforms;
+    for (let [, uniform] of uniforms) {
+      uniform.value = this._gl.getUniformLocation(program, uniform.name);
+    }
+  },
+
+  /**
+   * Gets the actual attribute location in a specific program.
+   * When relinked, all the attribute locations become obsolete and are updated
+   * in the cache. This method returns the (current) real attribute location.
+   *
+   * @param GLint initialValue
+   *        The initial attribute value.
+   * @return GLint
+   *         The current attribute value, or the initial value if it's already
+   *         up to date with its corresponding program.
+   */
+  getCurrentAttributeLocation: function (initialValue) {
+    let attributes = this._currentAttributesMap;
+    let currentInfo = attributes ? attributes[initialValue] : null;
+    return currentInfo ? currentInfo.value : initialValue;
+  },
+
+  /**
+   * Gets the actual uniform location in a specific program.
+   * When relinked, all the uniform locations become obsolete and are updated
+   * in the cache. This method returns the (current) real uniform location.
+   *
+   * @param WebGLUniformLocation initialValue
+   *        The initial uniform value.
+   * @return WebGLUniformLocation
+   *         The current uniform value, or the initial value if it's already
+   *         up to date with its corresponding program.
+   */
+  getCurrentUniformLocation: function (initialValue) {
+    let uniforms = this._currentUniformsMap;
+    let currentInfo = uniforms ? uniforms.get(initialValue) : null;
+    return currentInfo ? currentInfo.value : initialValue;
+  }
+};
+
+/**
+ * A mechanism for injecting or qureying state into/from a single WebGL context.
+ *
+ * Any interaction with a WebGL context should go through this proxy.
+ * Otherwise, the corresponding observer would register the calls as coming
+ * from content, which is usually not desirable. Infinite call stacks are bad.
+ *
+ * @param number id
+ *        The id of the window containing the WebGL context.
+ * @param WebGLRenderingContext context
+ *        The WebGL context used for the proxy methods.
+ * @param WebGLCache cache
+ *        The state storage for the corresponding context.
+ * @param WebGLObserver observer
+ *        The observer watching function calls in the corresponding context.
+ */
+function WebGLProxy(id, context, cache, observer) {
+  this._id = id;
+  this._gl = context;
+  this._cache = cache;
+  this._observer = observer;
+
+  let exports = [
+    "isEnabled",
+    "getParameter",
+    "getAttachedShaders",
+    "getShaderSource",
+    "getShaderOfType",
+    "compileShader",
+    "enableHighlighting",
+    "disableHighlighting",
+    "readPixels"
+  ];
+  exports.forEach(e => this[e] = (...args) => this._call(e, args));
+}
+
+WebGLProxy.prototype = {
+  _id: 0,
+  _gl: null,
+  _cache: null,
+  _observer: null,
+
+  get ownerWindow() {
+    return this._id;
+  },
+  get ownerContext() {
+    return this._gl;
+  },
+
+  /**
+   * Test whether a WebGL capability is enabled.
+   *
+   * @param string name
+   *        The WebGL capability name, for example "BLEND".
+   * @return boolean
+   *         True if enabled, false otherwise.
+   */
+  _isEnabled: function (name) {
+    return this._gl.isEnabled(this._gl[name]);
+  },
+
+  /**
+   * Returns the value for the specified WebGL parameter name.
+   *
+   * @param string name
+   *        The WebGL parameter name, for example "BLEND_COLOR".
+   * @return any
+   *         The corresponding parameter's value.
+   */
+  _getParameter: function (name) {
+    return this._gl.getParameter(this._gl[name]);
+  },
+
+  /**
+   * Returns the renderbuffer property value for the specified WebGL parameter.
+   * If no renderbuffer binding is available, null is returned.
+   *
+   * @param string name
+   *        The WebGL parameter name, for example "BLEND_COLOR".
+   * @return any
+   *         The corresponding parameter's value.
+   */
+  _getRenderbufferParameter: function (name) {
+    if (!this._getParameter("RENDERBUFFER_BINDING")) {
+      return null;
+    }
+    let gl = this._gl;
+    return gl.getRenderbufferParameter(gl.RENDERBUFFER, gl[name]);
+  },
+
+  /**
+   * Returns the framebuffer property value for the specified WebGL parameter.
+   * If no framebuffer binding is available, null is returned.
+   *
+   * @param string type
+   *        The framebuffer object attachment point, for example "COLOR_ATTACHMENT0".
+   * @param string name
+   *        The WebGL parameter name, for example "FRAMEBUFFER_ATTACHMENT_OBJECT_NAME".
+   *        If unspecified, defaults to "FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE".
+   * @return any
+   *         The corresponding parameter's value.
+   */
+  _getFramebufferAttachmentParameter: function (type, name = "FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE") {
+    if (!this._getParameter("FRAMEBUFFER_BINDING")) {
+      return null;
+    }
+    let gl = this._gl;
+    return gl.getFramebufferAttachmentParameter(gl.FRAMEBUFFER, gl[type], gl[name]);
+  },
+
+  /**
+   * Returns the shader objects attached to a program object.
+   *
+   * @param WebGLProgram program
+   *        The program for which to retrieve the attached shaders.
+   * @return array
+   *         The attached vertex and fragment shaders.
+   */
+  _getAttachedShaders: function (program) {
+    return this._gl.getAttachedShaders(program);
+  },
+
+  /**
+   * Returns the source code string from a shader object.
+   *
+   * @param WebGLShader shader
+   *        The shader for which to retrieve the source code.
+   * @return string
+   *         The shader's source code.
+   */
+  _getShaderSource: function (shader) {
+    return this._gl.getShaderSource(shader);
+  },
+
+  /**
+   * Finds a shader of the specified type in a list.
+   *
+   * @param WebGLShader[] shaders
+   *        The shaders for which to check the type.
+   * @param string type
+   *        Either "vertex" or "fragment".
+   * @return WebGLShader | null
+   *         The shader of the specified type, or null if nothing is found.
+   */
+  _getShaderOfType: function (shaders, type) {
+    let gl = this._gl;
+    let shaderTypeEnum = {
+      vertex: gl.VERTEX_SHADER,
+      fragment: gl.FRAGMENT_SHADER
+    }[type];
+
+    for (let shader of shaders) {
+      if (gl.getShaderParameter(shader, gl.SHADER_TYPE) == shaderTypeEnum) {
+        return shader;
+      }
+    }
+    return null;
+  },
+
+  /**
+   * Changes a shader's source code and relinks the respective program.
+   *
+   * @param WebGLProgram program
+   *        The program who's linked shader is to be modified.
+   * @param WebGLShader shader
+   *        The shader to be modified.
+   * @param string text
+   *        The new shader source code.
+   * @return object
+   *         An object containing the compilation and linking status.
+   */
+  _compileShader: function (program, shader, text) {
+    let gl = this._gl;
+    gl.shaderSource(shader, text);
+    gl.compileShader(shader);
+    gl.linkProgram(program);
+
+    let error = { compile: "", link: "" };
+
+    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
+      error.compile = gl.getShaderInfoLog(shader);
+    }
+    if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
+      error.link = gl.getShaderInfoLog(shader);
+    }
+
+    this._cache.updateAttributesForProgram(program);
+    this._cache.updateUniformsForProgram(program);
+
+    return error;
+  },
+
+  /**
+   * Enables color blending based on the geometry highlight tint.
+   */
+  _enableHighlighting: function () {
+    let gl = this._gl;
+
+    // Avoid changing the blending params when "rendering to texture".
+
+    // Check drawing to a custom framebuffer bound to the default renderbuffer.
+    let hasFramebuffer = this._getParameter("FRAMEBUFFER_BINDING");
+    let hasRenderbuffer = this._getParameter("RENDERBUFFER_BINDING");
+    if (hasFramebuffer && !hasRenderbuffer) {
+      return;
+    }
+
+    // Check drawing to a depth or stencil component of the framebuffer.
+    let writesDepth = this._getFramebufferAttachmentParameter("DEPTH_ATTACHMENT");
+    let writesStencil = this._getFramebufferAttachmentParameter("STENCIL_ATTACHMENT");
+    if (writesDepth || writesStencil) {
+      return;
+    }
+
+    // Non-premultiplied alpha blending based on a predefined constant color.
+    // Simply using gl.colorMask won't work, because we want non-tinted colors
+    // to be drawn as black, not ignored.
+    gl.enable(gl.BLEND);
+    gl.blendColor.apply(gl, this.highlightTint);
+    gl.blendEquation(gl.FUNC_ADD);
+    gl.blendFunc(gl.CONSTANT_COLOR, gl.ONE_MINUS_SRC_ALPHA, gl.CONSTANT_COLOR, gl.ZERO);
+    this.wasHighlighting = true;
+  },
+
+  /**
+   * Disables color blending based on the geometry highlight tint, by
+   * reverting the corresponding params back to their original values.
+   */
+  _disableHighlighting: function () {
+    let gl = this._gl;
+    let s = this._cache.currentState;
+
+    gl[s[gl.BLEND] ? "enable" : "disable"](gl.BLEND);
+    gl.blendColor.apply(gl, s.blendColor);
+    gl.blendEquationSeparate(s.blendEquationRgb, s.blendEquationAlpha);
+    gl.blendFuncSeparate(s.blendSrcRgb, s.blendDstRgb, s.blendSrcAlpha, s.blendDstAlpha);
+  },
+
+  /**
+   * Returns the pixel values at the position specified on the canvas.
+   */
+  _readPixels: function (x, y, w, h, format, type, buffer) {
+    this._gl.readPixels(x, y, w, h, format, type, buffer);
+  },
+
+  /**
+   * The color tint used for highlighting geometry.
+   * @see _enableHighlighting and _disableHighlighting.
+   */
+  highlightTint: [0, 0, 0, 0],
+
+  /**
+   * Executes a function in this object.
+   *
+   * This method makes sure that any handlers in the context observer are
+   * suppressed, hence stopping observing any context function calls.
+   *
+   * @param string funcName
+   *        The function to call.
+   * @param array args
+   *        An array of arguments.
+   * @return any
+   *         The called function result.
+   */
+  _call: function (funcName, args) {
+    let prevState = this._observer.suppressHandlers;
+
+    this._observer.suppressHandlers = true;
+    let result = this["_" + funcName].apply(this, args);
+    this._observer.suppressHandlers = prevState;
+
+    return result;
+  }
+};
+
+// Utility functions.
+
+function removeFromMap(map, predicate) {
+  for (let [key, value] of map) {
+    if (predicate(value)) {
+      map.delete(key);
+    }
+  }
+}
+
+function removeFromArray(array, predicate) {
+  for (let i = 0; i < array.length;) {
+    if (predicate(array[i])) {
+      array.splice(i, 1);
+    } else {
+      i++;
+    }
+  }
+}