function headlessCanvas() {
  return {
    headless: true,
    getContext: function(which) {
      switch(which) {
        case 'experimental-webgl': {
          return {
            /* ClearBufferMask */
            DEPTH_BUFFER_BIT               : 0x00000100,
            STENCIL_BUFFER_BIT             : 0x00000400,
            COLOR_BUFFER_BIT               : 0x00004000,
            
            /* BeginMode */
            POINTS                         : 0x0000,
            LINES                          : 0x0001,
            LINE_LOOP                      : 0x0002,
            LINE_STRIP                     : 0x0003,
            TRIANGLES                      : 0x0004,
            TRIANGLE_STRIP                 : 0x0005,
            TRIANGLE_FAN                   : 0x0006,
            
            /* AlphaFunction (not supported in ES20) */
            /*      NEVER */
            /*      LESS */
            /*      EQUAL */
            /*      LEQUAL */
            /*      GREATER */
            /*      NOTEQUAL */
            /*      GEQUAL */
            /*      ALWAYS */
            
            /* BlendingFactorDest */
            ZERO                           : 0,
            ONE                            : 1,
            SRC_COLOR                      : 0x0300,
            ONE_MINUS_SRC_COLOR            : 0x0301,
            SRC_ALPHA                      : 0x0302,
            ONE_MINUS_SRC_ALPHA            : 0x0303,
            DST_ALPHA                      : 0x0304,
            ONE_MINUS_DST_ALPHA            : 0x0305,
            
            /* BlendingFactorSrc */
            /*      ZERO */
            /*      ONE */
            DST_COLOR                      : 0x0306,
            ONE_MINUS_DST_COLOR            : 0x0307,
            SRC_ALPHA_SATURATE             : 0x0308,
            /*      SRC_ALPHA */
            /*      ONE_MINUS_SRC_ALPHA */
            /*      DST_ALPHA */
            /*      ONE_MINUS_DST_ALPHA */
            
            /* BlendEquationSeparate */
            FUNC_ADD                       : 0x8006,
            BLEND_EQUATION                 : 0x8009,
            BLEND_EQUATION_RGB             : 0x8009,   /* same as BLEND_EQUATION */
            BLEND_EQUATION_ALPHA           : 0x883D,
            
            /* BlendSubtract */
            FUNC_SUBTRACT                  : 0x800A,
            FUNC_REVERSE_SUBTRACT          : 0x800B,
            
            /* Separate Blend Functions */
            BLEND_DST_RGB                  : 0x80C8,
            BLEND_SRC_RGB                  : 0x80C9,
            BLEND_DST_ALPHA                : 0x80CA,
            BLEND_SRC_ALPHA                : 0x80CB,
            CONSTANT_COLOR                 : 0x8001,
            ONE_MINUS_CONSTANT_COLOR       : 0x8002,
            CONSTANT_ALPHA                 : 0x8003,
            ONE_MINUS_CONSTANT_ALPHA       : 0x8004,
            BLEND_COLOR                    : 0x8005,
            
            /* Buffer Objects */
            ARRAY_BUFFER                   : 0x8892,
            ELEMENT_ARRAY_BUFFER           : 0x8893,
            ARRAY_BUFFER_BINDING           : 0x8894,
            ELEMENT_ARRAY_BUFFER_BINDING   : 0x8895,
            
            STREAM_DRAW                    : 0x88E0,
            STATIC_DRAW                    : 0x88E4,
            DYNAMIC_DRAW                   : 0x88E8,
            
            BUFFER_SIZE                    : 0x8764,
            BUFFER_USAGE                   : 0x8765,
            
            CURRENT_VERTEX_ATTRIB          : 0x8626,
            
            /* CullFaceMode */
            FRONT                          : 0x0404,
            BACK                           : 0x0405,
            FRONT_AND_BACK                 : 0x0408,
            
            /* DepthFunction */
            /*      NEVER */
            /*      LESS */
            /*      EQUAL */
            /*      LEQUAL */
            /*      GREATER */
            /*      NOTEQUAL */
            /*      GEQUAL */
            /*      ALWAYS */
            
            /* EnableCap */
            /* TEXTURE_2D */
            CULL_FACE                      : 0x0B44,
            BLEND                          : 0x0BE2,
            DITHER                         : 0x0BD0,
            STENCIL_TEST                   : 0x0B90,
            DEPTH_TEST                     : 0x0B71,
            SCISSOR_TEST                   : 0x0C11,
            POLYGON_OFFSET_FILL            : 0x8037,
            SAMPLE_ALPHA_TO_COVERAGE       : 0x809E,
            SAMPLE_COVERAGE                : 0x80A0,
            
            /* ErrorCode */
            NO_ERROR                       : 0,
            INVALID_ENUM                   : 0x0500,
            INVALID_VALUE                  : 0x0501,
            INVALID_OPERATION              : 0x0502,
            OUT_OF_MEMORY                  : 0x0505,
            
            /* FrontFaceDirection */
            CW                             : 0x0900,
            CCW                            : 0x0901,
            
            /* GetPName */
            LINE_WIDTH                     : 0x0B21,
            ALIASED_POINT_SIZE_RANGE       : 0x846D,
            ALIASED_LINE_WIDTH_RANGE       : 0x846E,
            CULL_FACE_MODE                 : 0x0B45,
            FRONT_FACE                     : 0x0B46,
            DEPTH_RANGE                    : 0x0B70,
            DEPTH_WRITEMASK                : 0x0B72,
            DEPTH_CLEAR_VALUE              : 0x0B73,
            DEPTH_FUNC                     : 0x0B74,
            STENCIL_CLEAR_VALUE            : 0x0B91,
            STENCIL_FUNC                   : 0x0B92,
            STENCIL_FAIL                   : 0x0B94,
            STENCIL_PASS_DEPTH_FAIL        : 0x0B95,
            STENCIL_PASS_DEPTH_PASS        : 0x0B96,
            STENCIL_REF                    : 0x0B97,
            STENCIL_VALUE_MASK             : 0x0B93,
            STENCIL_WRITEMASK              : 0x0B98,
            STENCIL_BACK_FUNC              : 0x8800,
            STENCIL_BACK_FAIL              : 0x8801,
            STENCIL_BACK_PASS_DEPTH_FAIL   : 0x8802,
            STENCIL_BACK_PASS_DEPTH_PASS   : 0x8803,
            STENCIL_BACK_REF               : 0x8CA3,
            STENCIL_BACK_VALUE_MASK        : 0x8CA4,
            STENCIL_BACK_WRITEMASK         : 0x8CA5,
            VIEWPORT                       : 0x0BA2,
            SCISSOR_BOX                    : 0x0C10,
            /*      SCISSOR_TEST */
            COLOR_CLEAR_VALUE              : 0x0C22,
            COLOR_WRITEMASK                : 0x0C23,
            UNPACK_ALIGNMENT               : 0x0CF5,
            PACK_ALIGNMENT                 : 0x0D05,
            MAX_TEXTURE_SIZE               : 0x0D33,
            MAX_VIEWPORT_DIMS              : 0x0D3A,
            SUBPIXEL_BITS                  : 0x0D50,
            RED_BITS                       : 0x0D52,
            GREEN_BITS                     : 0x0D53,
            BLUE_BITS                      : 0x0D54,
            ALPHA_BITS                     : 0x0D55,
            DEPTH_BITS                     : 0x0D56,
            STENCIL_BITS                   : 0x0D57,
            POLYGON_OFFSET_UNITS           : 0x2A00,
            /*      POLYGON_OFFSET_FILL */
            POLYGON_OFFSET_FACTOR          : 0x8038,
            TEXTURE_BINDING_2D             : 0x8069,
            SAMPLE_BUFFERS                 : 0x80A8,
            SAMPLES                        : 0x80A9,
            SAMPLE_COVERAGE_VALUE          : 0x80AA,
            SAMPLE_COVERAGE_INVERT         : 0x80AB,
            
            /* GetTextureParameter */
            /*      TEXTURE_MAG_FILTER */
            /*      TEXTURE_MIN_FILTER */
            /*      TEXTURE_WRAP_S */
            /*      TEXTURE_WRAP_T */
            
            COMPRESSED_TEXTURE_FORMATS     : 0x86A3,
            
            /* HintMode */
            DONT_CARE                      : 0x1100,
            FASTEST                        : 0x1101,
            NICEST                         : 0x1102,
            
            /* HintTarget */
            GENERATE_MIPMAP_HINT            : 0x8192,
            
            /* DataType */
            BYTE                           : 0x1400,
            UNSIGNED_BYTE                  : 0x1401,
            SHORT                          : 0x1402,
            UNSIGNED_SHORT                 : 0x1403,
            INT                            : 0x1404,
            UNSIGNED_INT                   : 0x1405,
            FLOAT                          : 0x1406,
            
            /* PixelFormat */
            DEPTH_COMPONENT                : 0x1902,
            ALPHA                          : 0x1906,
            RGB                            : 0x1907,
            RGBA                           : 0x1908,
            LUMINANCE                      : 0x1909,
            LUMINANCE_ALPHA                : 0x190A,
            
            /* PixelType */
            /*      UNSIGNED_BYTE */
            UNSIGNED_SHORT_4_4_4_4         : 0x8033,
            UNSIGNED_SHORT_5_5_5_1         : 0x8034,
            UNSIGNED_SHORT_5_6_5           : 0x8363,
            
            /* Shaders */
            FRAGMENT_SHADER                  : 0x8B30,
            VERTEX_SHADER                    : 0x8B31,
            MAX_VERTEX_ATTRIBS               : 0x8869,
            MAX_VERTEX_UNIFORM_VECTORS       : 0x8DFB,
            MAX_VARYING_VECTORS              : 0x8DFC,
            MAX_COMBINED_TEXTURE_IMAGE_UNITS : 0x8B4D,
            MAX_VERTEX_TEXTURE_IMAGE_UNITS   : 0x8B4C,
            MAX_TEXTURE_IMAGE_UNITS          : 0x8872,
            MAX_FRAGMENT_UNIFORM_VECTORS     : 0x8DFD,
            SHADER_TYPE                      : 0x8B4F,
            DELETE_STATUS                    : 0x8B80,
            LINK_STATUS                      : 0x8B82,
            VALIDATE_STATUS                  : 0x8B83,
            ATTACHED_SHADERS                 : 0x8B85,
            ACTIVE_UNIFORMS                  : 0x8B86,
            ACTIVE_ATTRIBUTES                : 0x8B89,
            SHADING_LANGUAGE_VERSION         : 0x8B8C,
            CURRENT_PROGRAM                  : 0x8B8D,
            
            /* StencilFunction */
            NEVER                          : 0x0200,
            LESS                           : 0x0201,
            EQUAL                          : 0x0202,
            LEQUAL                         : 0x0203,
            GREATER                        : 0x0204,
            NOTEQUAL                       : 0x0205,
            GEQUAL                         : 0x0206,
            ALWAYS                         : 0x0207,
            
            /* StencilOp */
            /*      ZERO */
            KEEP                           : 0x1E00,
            REPLACE                        : 0x1E01,
            INCR                           : 0x1E02,
            DECR                           : 0x1E03,
            INVERT                         : 0x150A,
            INCR_WRAP                      : 0x8507,
            DECR_WRAP                      : 0x8508,
            
            /* StringName */
            VENDOR                         : 0x1F00,
            RENDERER                       : 0x1F01,
            VERSION                        : 0x1F02,
            
            /* TextureMagFilter */
            NEAREST                        : 0x2600,
            LINEAR                         : 0x2601,
            
            /* TextureMinFilter */
            /*      NEAREST */
            /*      LINEAR */
            NEAREST_MIPMAP_NEAREST         : 0x2700,
            LINEAR_MIPMAP_NEAREST          : 0x2701,
            NEAREST_MIPMAP_LINEAR          : 0x2702,
            LINEAR_MIPMAP_LINEAR           : 0x2703,
            
            /* TextureParameterName */
            TEXTURE_MAG_FILTER             : 0x2800,
            TEXTURE_MIN_FILTER             : 0x2801,
            TEXTURE_WRAP_S                 : 0x2802,
            TEXTURE_WRAP_T                 : 0x2803,
            
            /* TextureTarget */
            TEXTURE_2D                     : 0x0DE1,
            TEXTURE                        : 0x1702,
            
            TEXTURE_CUBE_MAP               : 0x8513,
            TEXTURE_BINDING_CUBE_MAP       : 0x8514,
            TEXTURE_CUBE_MAP_POSITIVE_X    : 0x8515,
            TEXTURE_CUBE_MAP_NEGATIVE_X    : 0x8516,
            TEXTURE_CUBE_MAP_POSITIVE_Y    : 0x8517,
            TEXTURE_CUBE_MAP_NEGATIVE_Y    : 0x8518,
            TEXTURE_CUBE_MAP_POSITIVE_Z    : 0x8519,
            TEXTURE_CUBE_MAP_NEGATIVE_Z    : 0x851A,
            MAX_CUBE_MAP_TEXTURE_SIZE      : 0x851C,
            
            /* TextureUnit */
            TEXTURE0                       : 0x84C0,
            TEXTURE1                       : 0x84C1,
            TEXTURE2                       : 0x84C2,
            TEXTURE3                       : 0x84C3,
            TEXTURE4                       : 0x84C4,
            TEXTURE5                       : 0x84C5,
            TEXTURE6                       : 0x84C6,
            TEXTURE7                       : 0x84C7,
            TEXTURE8                       : 0x84C8,
            TEXTURE9                       : 0x84C9,
            TEXTURE10                      : 0x84CA,
            TEXTURE11                      : 0x84CB,
            TEXTURE12                      : 0x84CC,
            TEXTURE13                      : 0x84CD,
            TEXTURE14                      : 0x84CE,
            TEXTURE15                      : 0x84CF,
            TEXTURE16                      : 0x84D0,
            TEXTURE17                      : 0x84D1,
            TEXTURE18                      : 0x84D2,
            TEXTURE19                      : 0x84D3,
            TEXTURE20                      : 0x84D4,
            TEXTURE21                      : 0x84D5,
            TEXTURE22                      : 0x84D6,
            TEXTURE23                      : 0x84D7,
            TEXTURE24                      : 0x84D8,
            TEXTURE25                      : 0x84D9,
            TEXTURE26                      : 0x84DA,
            TEXTURE27                      : 0x84DB,
            TEXTURE28                      : 0x84DC,
            TEXTURE29                      : 0x84DD,
            TEXTURE30                      : 0x84DE,
            TEXTURE31                      : 0x84DF,
            ACTIVE_TEXTURE                 : 0x84E0,
            
            /* TextureWrapMode */
            REPEAT                         : 0x2901,
            CLAMP_TO_EDGE                  : 0x812F,
            MIRRORED_REPEAT                : 0x8370,
            
            /* Uniform Types */
            FLOAT_VEC2                     : 0x8B50,
            FLOAT_VEC3                     : 0x8B51,
            FLOAT_VEC4                     : 0x8B52,
            INT_VEC2                       : 0x8B53,
            INT_VEC3                       : 0x8B54,
            INT_VEC4                       : 0x8B55,
            BOOL                           : 0x8B56,
            BOOL_VEC2                      : 0x8B57,
            BOOL_VEC3                      : 0x8B58,
            BOOL_VEC4                      : 0x8B59,
            FLOAT_MAT2                     : 0x8B5A,
            FLOAT_MAT3                     : 0x8B5B,
            FLOAT_MAT4                     : 0x8B5C,
            SAMPLER_2D                     : 0x8B5E,
            SAMPLER_CUBE                   : 0x8B60,
            
            /* Vertex Arrays */
            VERTEX_ATTRIB_ARRAY_ENABLED        : 0x8622,
            VERTEX_ATTRIB_ARRAY_SIZE           : 0x8623,
            VERTEX_ATTRIB_ARRAY_STRIDE         : 0x8624,
            VERTEX_ATTRIB_ARRAY_TYPE           : 0x8625,
            VERTEX_ATTRIB_ARRAY_NORMALIZED     : 0x886A,
            VERTEX_ATTRIB_ARRAY_POINTER        : 0x8645,
            VERTEX_ATTRIB_ARRAY_BUFFER_BINDING : 0x889F,
            
            /* Shader Source */
            COMPILE_STATUS                 : 0x8B81,
            
            /* Shader Precision-Specified Types */
            LOW_FLOAT                      : 0x8DF0,
            MEDIUM_FLOAT                   : 0x8DF1,
            HIGH_FLOAT                     : 0x8DF2,
            LOW_INT                        : 0x8DF3,
            MEDIUM_INT                     : 0x8DF4,
            HIGH_INT                       : 0x8DF5,
            
            /* Framebuffer Object. */
            FRAMEBUFFER                    : 0x8D40,
            RENDERBUFFER                   : 0x8D41,
            
            RGBA4                          : 0x8056,
            RGB5_A1                        : 0x8057,
            RGB565                         : 0x8D62,
            DEPTH_COMPONENT16              : 0x81A5,
            STENCIL_INDEX                  : 0x1901,
            STENCIL_INDEX8                 : 0x8D48,
            DEPTH_STENCIL                  : 0x84F9,
            
            RENDERBUFFER_WIDTH             : 0x8D42,
            RENDERBUFFER_HEIGHT            : 0x8D43,
            RENDERBUFFER_INTERNAL_FORMAT   : 0x8D44,
            RENDERBUFFER_RED_SIZE          : 0x8D50,
            RENDERBUFFER_GREEN_SIZE        : 0x8D51,
            RENDERBUFFER_BLUE_SIZE         : 0x8D52,
            RENDERBUFFER_ALPHA_SIZE        : 0x8D53,
            RENDERBUFFER_DEPTH_SIZE        : 0x8D54,
            RENDERBUFFER_STENCIL_SIZE      : 0x8D55,
            
            FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE           : 0x8CD0,
            FRAMEBUFFER_ATTACHMENT_OBJECT_NAME           : 0x8CD1,
            FRAMEBUFFER_ATTACHMENT_TEXTURE_LEVEL         : 0x8CD2,
            FRAMEBUFFER_ATTACHMENT_TEXTURE_CUBE_MAP_FACE : 0x8CD3,
            
            COLOR_ATTACHMENT0              : 0x8CE0,
            DEPTH_ATTACHMENT               : 0x8D00,
            STENCIL_ATTACHMENT             : 0x8D20,
            DEPTH_STENCIL_ATTACHMENT       : 0x821A,
            
            NONE                           : 0,
            
            FRAMEBUFFER_COMPLETE                      : 0x8CD5,
            FRAMEBUFFER_INCOMPLETE_ATTACHMENT         : 0x8CD6,
            FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT : 0x8CD7,
            FRAMEBUFFER_INCOMPLETE_DIMENSIONS         : 0x8CD9,
            FRAMEBUFFER_UNSUPPORTED                   : 0x8CDD,
            
            FRAMEBUFFER_BINDING            : 0x8CA6,
            RENDERBUFFER_BINDING           : 0x8CA7,
            MAX_RENDERBUFFER_SIZE          : 0x84E8,
            
            INVALID_FRAMEBUFFER_OPERATION  : 0x0506,
            
            /* WebGL-specific enums */
            UNPACK_FLIP_Y_WEBGL            : 0x9240,
            UNPACK_PREMULTIPLY_ALPHA_WEBGL : 0x9241,
            CONTEXT_LOST_WEBGL             : 0x9242,
            UNPACK_COLORSPACE_CONVERSION_WEBGL : 0x9243,
            BROWSER_DEFAULT_WEBGL          : 0x9244,

            items: {},
            id: 0,
            getExtension: function() { return 1 },
            createBuffer: function() {
              var id = this.id++;
              this.items[id] = {
                which: 'buffer',
              };
              return id;
            },
            deleteBuffer: function(){},
            bindBuffer: function(){},
            bufferData: function(){},
            getParameter: function(pname) {
              switch(pname) {
                case /* GL_VENDOR                           */ 0x1F00: return 'FakeShellGLVendor';
                case /* GL_RENDERER                         */ 0x1F01: return 'FakeShellGLRenderer';
                case /* GL_VERSION                          */ 0x1F02: return '0.0.1';
                case /* GL_MAX_TEXTURE_SIZE                 */ 0x0D33: return 16384;
                case /* GL_MAX_CUBE_MAP_TEXTURE_SIZE        */ 0x851C: return 16384;
                case /* GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT   */ 0x84FF: return 16;
                case /* GL_MAX_TEXTURE_IMAGE_UNITS_NV       */ 0x8872: return 16;
                case /* GL_MAX_VERTEX_UNIFORM_VECTORS       */ 0x8DFB: return 4096;
                case /* GL_MAX_FRAGMENT_UNIFORM_VECTORS     */ 0x8DFD: return 4096;
                case /* GL_MAX_VARYING_VECTORS              */ 0x8DFC: return 32;
                case /* GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS */ 0x8B4D: return 32;
                case /* GL_ARRAY_BUFFER_BINDING             */ 0x8894: return 0;
                default: console.log('getParameter ' + pname + '?'); return 0;
              }
            },
            getSupportedExtensions: function() {
              return ["OES_texture_float", "OES_standard_derivatives", "EXT_texture_filter_anisotropic", "MOZ_EXT_texture_filter_anisotropic", "MOZ_WEBGL_lose_context", "MOZ_WEBGL_compressed_texture_s3tc", "MOZ_WEBGL_depth_texture"];
            },
            createShader: function(type) {
              var id = this.id++;
              this.items[id] = {
                which: 'shader',
                type: type,
              };
              return id;
            },
            getShaderParameter: function(shader, pname) {
              switch(pname) {
                case /* GL_SHADER_TYPE    */ 0x8B4F: return this.items[shader].type;
                case /* GL_COMPILE_STATUS */ 0x8B81: return true;
                default: throw 'getShaderParameter ' + pname;
              }
            },
            shaderSource: function(){},
            compileShader: function(){},
            createProgram: function() {
              var id = this.id++;
              this.items[id] = {
                which: 'program',
                shaders: [],
              };
              return id;
            },
            attachShader: function(program, shader) {
              this.items[program].shaders.push(shader);
            },
            bindAttribLocation: function(){},
            linkProgram: function(){},
            getProgramParameter: function(program, pname) {
              switch(pname) {
                case /* LINK_STATUS     */ 0x8B82: return true;
                case /* ACTIVE_UNIFORMS */ 0x8B86: return 4;
                default: throw 'getProgramParameter ' + pname;
              }
            },
            deleteShader: function(){},
            deleteProgram: function(){},
            viewport: function(){},
            clearColor: function(){},
            clearDepth: function(){},
            depthFunc: function(){},
            enable: function(){},
            disable: function(){},
            frontFace: function(){},
            cullFace: function(){},
            activeTexture: function(){},
            createTexture: function() {
              var id = this.id++;
              this.items[id] = {
                which: 'texture',
              };
              return id;
            },
            deleteTexture: function(){},
            boundTextures: {},
            bindTexture: function(target, texture) {
              this.boundTextures[target] = texture;
            },
            texParameteri: function(){},
            pixelStorei: function(){},
            texImage2D: function(){},
            compressedTexImage2D: function(){},
            useProgram: function(){},
            getUniformLocation: function() {
              return null;
            },
            getActiveUniform: function(program, index) {
              return {
                size: 1,
                type: /* INT_VEC3 */ 0x8B54,
                name: 'activeUniform' + index,
              };
            },
            clear: function(){},
            uniform4fv: function(){},
            uniform1i: function(){},
            getAttribLocation: function() { return 1 },
            vertexAttribPointer: function(){},
            enableVertexAttribArray: function(){},
            disableVertexAttribArray: function(){},
            drawElements: function(){},
            drawArrays: function(){},
            depthMask: function(){},
            depthRange: function(){},
            bufferSubData: function(){},
            blendFunc: function(){},
            createFramebuffer: function() {
              var id = this.id++;
              this.items[id] = {
                which: 'framebuffer',
                shaders: [],
              };
              return id;
            },
            bindFramebuffer: function(){},
            framebufferTexture2D: function(){},
            checkFramebufferStatus: function() {
              return /* FRAMEBUFFER_COMPLETE */ 0x8CD5;
            },
            createRenderbuffer: function() {
              var id = this.id++;
              this.items[id] = {
                which: 'renderbuffer',
                shaders: [],
              };
              return id;
            },
            bindRenderbuffer: function(){},
            renderbufferStorage: function(){},
            framebufferRenderbuffer: function(){},
            scissor: function(){},
            colorMask: function(){},
            lineWidth: function(){},
            vertexAttrib4fv: function(){},
          };
        }
        case '2d': {
          return {
            drawImage: function(){},
            getImageData: function(x, y, w, h) {
              return {
                width: w,
                height: h,
                data: new Uint8ClampedArray(w*h),
              };
            },
            save: function(){},
            restore: function(){},
            fillRect: function(){},
            measureText: function() { return 10 },
            fillText: function(){},
          };
        }
        default: throw 'canvas.getContext: ' + which;
      }
    },
    requestPointerLock: function() {
      document.pointerLockElement = document.getElementById('canvas');
      window.setTimeout(function() {
        document.callEventListeners('pointerlockchange');
      });
    },
    exitPointerLock: function(){},
    style: {
      setProperty: function(){}
    },
    eventListeners: {},
    addEventListener: function(){},
    removeEventListener: function(){},
    requestFullScreen: function() {
      document.fullscreenElement = document.getElementById('canvas');
      window.setTimeout(function() {
        document.callEventListeners('fullscreenchange');
      });
    },
    offsetTop: 0,
    offsetLeft: 0,
    // generics
    classList: {
      add: function(){},
      remove: function(){},
    },
  };
}