Added "darker" composite op

Readme.md

@@ -11,7 +11,7 @@
 
     $ npm install canvas
 
-If not previously installed, you will want to install the [cairo graphics library](http://cairographics.org/download/) version _>= 1.8.6_ first using the package manager available to you, or [building from source](https://github.com/LearnBoost/node-canvas/wiki/_pages).
+If not previously installed, you will want to install the [cairo graphics library](http://cairographics.org/download/) version _>= 1.10.0_ first using the package manager available to you, or [building from source](https://github.com/LearnBoost/node-canvas/wiki/_pages).
 
 ## Screencasts
 

src/CanvasRenderingContext2d.cc

@@ -448,7 +448,9 @@ Context2d::SetGlobalCompositeOperation(Local<String> prop, Local<Value> val, con
   if (0 == strcmp("xor", *type)) {
     cairo_set_operator(ctx, CAIRO_OPERATOR_XOR);
   }else if (0 == strcmp("lighter", *type)) {
-    cairo_set_operator(ctx, CAIRO_OPERATOR_ADD);
+    cairo_set_operator(ctx, CAIRO_OPERATOR_LIGHTEN);
+  }else if (0 == strcmp("darker", *type)) {
+    cairo_set_operator(ctx, CAIRO_OPERATOR_DARKEN);
   }else if (0 == strcmp("source-atop", *type)) {
     cairo_set_operator(ctx, CAIRO_OPERATOR_ATOP);
   } else if (0 == strcmp("source-in", *type)) {

test/public/tests.js

@@ -919,6 +919,15 @@ tests['globalCompositeOperation lighter'] = function(ctx){
   ctx.fill();
 };
 
+tests['globalCompositeOperation darker'] = function(ctx){
+  ctx.fillStyle = 'blue';
+  ctx.fillRect(0,0,100,100);
+  ctx.globalCompositeOperation = 'darker';
+  ctx.fillStyle = 'red';
+  ctx.arc(80,80,50,0,Math.PI * 2);
+  ctx.fill();
+};
+
 tests['shadowBlur'] = function(ctx){
   ctx.fillRect(150,10,20,20);