Added createImageData()

lib/context2d.js

@@ -466,4 +466,18 @@ Context2d.prototype.__defineGetter__('textAlign', function(){
 Context2d.prototype.getImageData = function(x, y, width, height){
   var arr = new PixelArray(this.canvas, x, y, width, height);
   return new ImageData(arr);
+};
+
+/**
+ * Create `ImageData` with the given dimensions.
+ *
+ * @param {Number} width
+ * @param {Number} height
+ * @return {ImageData}
+ * @api public
+ */
+
+Context2d.prototype.createImageData = function(width, height){
+  var arr = new PixelArray(width, height);
+  return new ImageData(arr);
 };

src/PixelArray.cc

@@ -75,21 +75,21 @@ PixelArray::GetLength(Local<String> prop, const AccessorInfo &info) {
 }
 
 /*
- * Initialize a new PixelArray.
+ * Initialize a new PixelArray copying data
+ * from the canvas surface using the given rect.
  */
 
 PixelArray::PixelArray(Canvas *canvas, int sx, int sy, int width, int height):
   _width(width), _height(height) {
 
   // Alloc space for our new data
-  _stride = width * 4;
+  uint8_t *dst = alloc();
-  uint8_t *dst = _data = (uint8_t *) malloc(length());
-  memset(_data, 0, length());
   uint8_t *src = canvas->data();
+  int s = stride();
 
   // Normalize data (argb -> rgba)
   for (int y = 0; y < height; ++y) {
-    uint32_t *row = (uint32_t *)(src + _stride * y);
+    uint32_t *row = (uint32_t *)(src + s * y);
     for (int x = 0; x < width; ++x) {
       int bx = x * 4;
       uint32_t *pixel = row + x;
@@ -101,14 +101,28 @@ PixelArray::PixelArray(Canvas *canvas, int sx, int sy, int width, int height):
       dst[bx + 1] = (*pixel >> 8) * 255 / a;
       dst[bx + 2] = *pixel * 255 / a;
     }
-    dst += _stride;
+    dst += s;
   }
 }
 
+/*
+ * Initialize an empty PixelArray with the given dimensions.
+ */
+
 PixelArray::PixelArray(int width, int height):
   _width(width), _height(height) {
-  // TODO: error handling
+  alloc();
-  // TODO: implement
+}
+
+/*
+ * Allocate / zero data buffer.
+ */
+
+uint8_t *
+PixelArray::alloc() {
+  _data = (uint8_t *) malloc(length());
+  memset(_data, 0, length());
+  return _data;
 }
 
 PixelArray::~PixelArray() {

src/PixelArray.h

@@ -18,13 +18,13 @@ class PixelArray: public node::ObjectWrap {
     inline int length(){ return _width * _height * 4; }
     inline int width(){ return _width; }
     inline int height(){ return _height; }
-    inline int stride(){ return _stride; }
+    inline int stride(){ return _width * 4; }
     inline uint8_t *data(){ return _data; }
     PixelArray(Canvas *canvas, int x, int y, int width, int height);
     PixelArray(int width, int height);
     ~PixelArray();
   private:
-    int _stride;
+    uint8_t *alloc();
     uint8_t *_data;
     int _width, _height;
 };