Better offscreen detetion, added parameter to skip offscreen rendering.

src/mixins/object_geometry.mixin.js

@@ -164,6 +164,15 @@
           return true;
         }
       }
+      // no points on screen, check intersection with absolute coordinates
+      if (this.intersectsWithRect(pointTL, pointBR, true)) {
+        return true;
+      }
+      // worst case scenario the object is so big that contanins the screen
+      var centerPoint = { x: (pointTL.x + pointBR.x) / 2, y: (pointTL.y + pointBR.y) / 2 };
+      if (this.containsPoint(centerPoint, null, true)) {
+        return true;
+      }
       return false;
     },
 

src/shapes/object.class.js

@@ -1134,6 +1134,9 @@
       if ((this.width === 0 && this.height === 0) || !this.visible) {
         return;
       }
+      if (this.canvas && this.canvas.skipOffscreen && !this.group && !this.isOnScreen()) {
+        return;
+      }
       ctx.save();
       //setup fill rule for current object
       this._setupCompositeOperation(ctx);

src/shapes/text.class.js

@@ -849,6 +849,9 @@
       if (!this.visible) {
         return;
       }
+      if (this.canvas && this.canvas.skipOffscreen && !this.group && !this.isOnScreen()) {
+        return;
+      }
       if (this._shouldClearDimensionCache()) {
         this._setTextStyles(ctx);
         this._initDimensions(ctx);

src/static_canvas.class.js

@@ -181,6 +181,16 @@
      */
     vptCoords: { },
 
+    /**
+     * Based on vptCoords and object.aCoords, skip rendering of objects that
+     * are not included in current viewport.
+     * May greatly help in applications with crowded canvas and use of zoom/pan
+     * If One of the corner of the bounding box of the object is on the canvas
+     * the objects get rendered.
+     * @memberOf fabric.StaticCanvas.prototype
+     */
+    skipOffscreen: true,
+
     /**
      * @private
      * @param {HTMLElement | String} el <canvas> element to initialize instance on

test/unit/object_geometry.js

@@ -331,6 +331,31 @@
     ok(cObj.isOnScreen(), 'zooming out the object is again on screen');
   });
 
+  test('isOnScreen with object that include canvas', function(){
+    var cObj = new fabric.Object(
+      { left: -10, top: -10, width: canvas.getWidth() + 100, height: canvas.getHeight(), strokeWidth: 0});
+    canvas.viewportTransform = [1, 0, 0, 1, 0, 0];
+    cObj.canvas = canvas;
+    cObj.setCoords();
+    equal(cObj.isOnScreen(), true, 'object is onScreen because it include the canvas');
+    cObj.top = -1000;
+    cObj.left = -1000;
+    cObj.setCoords();
+    equal(cObj.isOnScreen(), false, 'object is completely out of viewport');
+  });
+
+  test('isOnScreen with object that is in top left corner of canvas', function(){
+    var cObj = new fabric.Rect({left: -46.56, top: -9.23, width: 50,height: 50, angle: 314.57});
+    canvas.viewportTransform = [1, 0, 0, 1, 0, 0];
+    cObj.canvas = canvas;
+    cObj.setCoords();
+    ok(cObj.isOnScreen(), 'object is onScreen because it intersect a canvas line');
+    cObj.top -= 20;
+    cObj.left -= 20;
+    cObj.setCoords();
+    ok(!cObj.isOnScreen(), 'object is completely out of viewport');
+  });
+
   test('calcTransformMatrix', function(){
     var cObj = new fabric.Object({ width: 10, height: 15, strokeWidth: 0 });
     ok(typeof cObj.calcTransformMatrix == 'function', 'calcTransformMatrix should exist');