pdfjs-dist/worker/canvas.js

/* -*- Mode: Java; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set shiftwidth=2 tabstop=2 autoindent cindent expandtab: */

'use strict';

var JpegStreamProxyCounter = 0;
// WebWorker Proxy for JpegStream.
var JpegStreamProxy = (function() {
  function constructor(bytes, dict) {
    this.id = JpegStreamProxyCounter++;
    this.dict = dict;

    // Tell the main thread to create an image.
    postMessage({
      action: 'jpeg_stream',
      data: {
        id: this.id,
        raw: bytesToString(bytes)
      }
    });
  }

  constructor.prototype = {
    getImage: function() {
      return this;
    },
    getChar: function() {
      error('internal error: getChar is not valid on JpegStream');
    }
  };

  return constructor;
})();

// Really simple GradientProxy. There is currently only one active gradient at
// the time, meaning you can't create a gradient, create a second one and then
// use the first one again. As this isn't used in pdf.js right now, it's okay.
function GradientProxy(cmdQueue, x0, y0, x1, y1) {
  cmdQueue.push(['$createLinearGradient', [x0, y0, x1, y1]]);
  this.addColorStop = function(i, rgba) {
    cmdQueue.push(['$addColorStop', [i, rgba]]);
  };
}

// Really simple PatternProxy.
var patternProxyCounter = 0;
function PatternProxy(cmdQueue, object, kind) {
  this.id = patternProxyCounter++;

  if (!(object instanceof CanvasProxy)) {
    throw 'unkown type to createPattern';
  }

  // Flush the object here to ensure it's available on the main thread.
  // TODO: Make some kind of dependency management, such that the object
  // gets flushed only if needed.
  object.flush();
  cmdQueue.push(['$createPatternFromCanvas', [this.id, object.id, kind]]);
}

var canvasProxyCounter = 0;
function CanvasProxy(width, height) {
  this.id = canvasProxyCounter++;

  // The `stack` holds the rendering calls and gets flushed to the main thead.
  var cmdQueue = this.cmdQueue = [];

  // Dummy context that gets exposed.
  var ctx = {};
  this.getContext = function(type) {
    if (type != '2d') {
      throw 'CanvasProxy can only provide a 2d context.';
    }
    return ctx;
  };

  // Expose only the minimum of the canvas object - there is no dom to do
  // more here.
  this.width = width;
  this.height = height;
  ctx.canvas = this;

  // Setup function calls to `ctx`.
  var ctxFunc = [
  'createRadialGradient',
  'arcTo',
  'arc',
  'fillText',
  'strokeText',
  'createImageData',
  'drawWindow',
  'save',
  'restore',
  'scale',
  'rotate',
  'translate',
  'transform',
  'setTransform',
  'clearRect',
  'fillRect',
  'strokeRect',
  'beginPath',
  'closePath',
  'moveTo',
  'lineTo',
  'quadraticCurveTo',
  'bezierCurveTo',
  'rect',
  'fill',
  'stroke',
  'clip',
  'measureText',
  'isPointInPath',

  // These functions are necessary to track the rendering currentX state.
  // The exact values can be computed on the main thread only, as the
  // worker has no idea about text width.
  '$setCurrentX',
  '$addCurrentX',
  '$saveCurrentX',
  '$restoreCurrentX',
  '$showText',
  '$setFont'
  ];

  function buildFuncCall(name) {
    return function() {
      // console.log("funcCall", name)
      cmdQueue.push([name, Array.prototype.slice.call(arguments)]);
    };
  }
  var name;
  for (var i = 0; i < ctxFunc.length; i++) {
    name = ctxFunc[i];
    ctx[name] = buildFuncCall(name);
  }

  // Some function calls that need more work.

  ctx.createPattern = function(object, kind) {
    return new PatternProxy(cmdQueue, object, kind);
  };

  ctx.createLinearGradient = function(x0, y0, x1, y1) {
    return new GradientProxy(cmdQueue, x0, y0, x1, y1);
  };

  ctx.getImageData = function(x, y, w, h) {
    return {
      width: w,
      height: h,
      data: Uint8ClampedArray(w * h * 4)
    };
  };

  ctx.putImageData = function(data, x, y, width, height) {
    cmdQueue.push(['$putImageData', [data, x, y, width, height]]);
  };

  ctx.drawImage = function(image, x, y, width, height,
                           sx, sy, swidth, sheight) {
    if (image instanceof CanvasProxy) {
      // Send the image/CanvasProxy to the main thread.
      image.flush();
      cmdQueue.push(['$drawCanvas', [image.id, x, y, sx, sy, swidth, sheight]]);
    } else if (image instanceof JpegStreamProxy) {
      cmdQueue.push(['$drawImage', [image.id, x, y, sx, sy, swidth, sheight]]);
    } else {
      throw 'unkown type to drawImage';
    }
  };

  // Setup property access to `ctx`.
  var ctxProp = {
    // "canvas"
    'globalAlpha': '1',
    'globalCompositeOperation': 'source-over',
    'strokeStyle': '#000000',
    'fillStyle': '#000000',
    'lineWidth': '1',
    'lineCap': 'butt',
    'lineJoin': 'miter',
    'miterLimit': '10',
    'shadowOffsetX': '0',
    'shadowOffsetY': '0',
    'shadowBlur': '0',
    'shadowColor': 'rgba(0, 0, 0, 0)',
    'font': '10px sans-serif',
    'textAlign': 'start',
    'textBaseline': 'alphabetic',
    'mozTextStyle': '10px sans-serif',
    'mozImageSmoothingEnabled': 'true'
  };

  function buildGetter(name) {
    return function() {
      return ctx['$' + name];
    };
  }

  function buildSetter(name) {
    return function(value) {
      cmdQueue.push(['$', name, value]);
      return (ctx['$' + name] = value);
    };
  }

  // Setting the value to `stroke|fillStyle` needs special handling, as it
  // might gets an gradient/pattern.
  function buildSetterStyle(name) {
    return function(value) {
      if (value instanceof GradientProxy) {
        cmdQueue.push(['$' + name + 'Gradient']);
      } else if (value instanceof PatternProxy) {
        cmdQueue.push(['$' + name + 'Pattern', [value.id]]);
      } else {
        cmdQueue.push(['$', name, value]);
        return (ctx['$' + name] = value);
      }
    };
  }

  for (var name in ctxProp) {
    ctx['$' + name] = ctxProp[name];
    ctx.__defineGetter__(name, buildGetter(name));

    // Special treatment for `fillStyle` and `strokeStyle`: The passed style
    // might be a gradient. Need to check for that.
    if (name == 'fillStyle' || name == 'strokeStyle') {
      ctx.__defineSetter__(name, buildSetterStyle(name));
    } else {
      ctx.__defineSetter__(name, buildSetter(name));
    }
  }
}

/**
* Sends the current cmdQueue of the CanvasProxy over to the main thread and
* resets the cmdQueue.
*/
CanvasProxy.prototype.flush = function() {
  postMessage({
    action: 'canvas_proxy_cmd_queue',
    data: {
      id: this.id,
      cmdQueue: this.cmdQueue,
      width: this.width,
      height: this.height
    }
  });
  this.cmdQueue.length = 0;
};