canvas-currentTransform/currentTransform.js at master · goessner/canvas-currentTransform · GitHub

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/**
 * @fileoverview Implement 'currentTransform' of CanvasRenderingContext2D prototype (polyfill)
 * @author Stefan Goessner (c) 2015
 */

/**
 * extend CanvasRenderingContext2D.prototype by current transformation matrix access.
 */
if (!("currentTransform" in CanvasRenderingContext2D.prototype)) {
/**
 * define property 'currentTransform'
 */
   if ("mozCurrentTransform" in CanvasRenderingContext2D.prototype) {
      Object.defineProperty(CanvasRenderingContext2D.prototype, "currentTransform", {
         get : function() { var m = this.mozCurrentTransform; return {a:m[0],b:m[1],c:m[2],d:m[3],e:m[4],f:m[5]}; },
         set : function(x) { this.mozCurrentTransform = [x.a,x.b,x.c,x.d,x.e,x.f]; },
         enumerable : true,
         configurable : false
      });
   }
   else if ("webkitCurrentTransform" in CanvasRenderingContext2D.prototype) {
      Object.defineProperty(CanvasRenderingContext2D.prototype, "currentTransform", {
         get : function() { return this.webkitCurrentTransform; },
         set : function(x) { this.webkitCurrentTransform = x; },
         enumerable : true,
         configurable : false
      });
   }
   else {  // fully implement it ... hmm ... 'currentTransform', 'save()', 'restore()', 'transform()', 'setTransform()', 'resetTransform()'
      Object.defineProperty(CanvasRenderingContext2D.prototype, "currentTransform", {
         get : function() {return this._t2stack && this._t2stack[this._t2stack.length-1] || {a:1,b:0,c:0,d:1,e:0,f:0};},
         set : function(x) {
            if (!this._t2stack)
               this._t2stack = [{}];
            this._t2stack[this._t2stack.length-1] = {a:x.a,b:x.b,c:x.c,d:x.d,e:x.e,f:x.f};
         },
         enumerable : true,
         configurable : false
      });
      CanvasRenderingContext2D.prototype.save = function() {
         var save = CanvasRenderingContext2D.prototype.save;
         return function() {
            if (!this._t2stack)
               this._t2stack = [{a:1,b:0,c:0,d:1,e:0,f:0}];
            var t = this._t2stack[this._t2stack.length-1];
            this._t2stack.push(t && {a:t.a,b:t.b,c:t.c,d:t.d,e:t.e,f:t.f});
            save.call(this);
         }
      }();
      CanvasRenderingContext2D.prototype.restore = function() {
         var restore = CanvasRenderingContext2D.prototype.restore;
         return function() {
            if (this._t2stack) this._t2stack.pop();
            restore.call(this);
         }
      }();
      CanvasRenderingContext2D.prototype.transform = function() {
         var transform = CanvasRenderingContext2D.prototype.transform;
         return function(a,b,c,d,e,f) {
            if (!this._t2stack)
               this._t2stack = [{a:1,b:0,c:0,d:1,e:0,f:0}];
            var t = this._t2stack[this._t2stack.length-1], q;

            var na = t.a*a + t.c * b;
            var nb = t.b*a + t.d * b;

            var nc = t.a*c + t.c * d;
            var nd = t.b*c + t.d * d;

            var ne = t.e + t.a*e + t.c*f;
            var nf = t.f + t.b*e + t.d*f;

            t.a = na;
            t.b = nb;
            t.c = nc;
            t.d = nd;
            t.e = ne;
            t.f = nf;
            transform.call(this,a,b,c,d,e,f);
         }
      }();
      CanvasRenderingContext2D.prototype.setTransform = function() {
         var setTransform = CanvasRenderingContext2D.prototype.setTransform;
         return function(a,b,c,d,e,f) {
            if (!this._t2stack)
               this._t2stack = [{}];
            this._t2stack[this._t2stack.length-1] = {a:a,b:b,c:c,d:d,e:e,f:f};
            setTransform.call(this,a,b,c,d,e,f);
         }
      }();
      CanvasRenderingContext2D.prototype.resetTransform = function() {
         var resetTransform = CanvasRenderingContext2D.prototype.resetTransform;
         return function() {
            if (!this._t2stack)
               this._t2stack = [{}];
            this._t2stack[this._t2stack.length-1] = {a:1,b:0,c:0,d:1,e:0,f:0};
            resetTransform && resetTransform.call(this);
         }
      }();
      CanvasRenderingContext2D.prototype.scale = function() {
         var scale = CanvasRenderingContext2D.prototype.scale;
         return function(sx,sy) {
            if (!this._t2stack)
               this._t2stack = [{a:1,b:0,c:0,d:1,e:0,f:0}];
            var t = this._t2stack[this._t2stack.length-1];
            sx = sx || 1;
            sy = sy || sx;
            t.a *= sx; t.c *= sy;
            t.b *= sx; t.d *= sy;
            scale.call(this,sx,sy);
         }
      }();
      CanvasRenderingContext2D.prototype.rotate = function() {
         var rotate = CanvasRenderingContext2D.prototype.rotate;
         return function(w) {
            if (!this._t2stack)
               this._t2stack = [{a:1,b:0,c:0,d:1,e:0,f:0}];
            var t = this._t2stack[this._t2stack.length-1];

            var cw = Math.cos(-w);
            var sw = Math.sin(-w);

            var a = t.a*cw - t.c*sw;
            var b = t.b*cw - t.d*sw;
            var c = t.c*cw + t.a*sw;
            var d = t.d*cw + t.b*sw;

            t.a = a;
            t.b = b;
            t.c = c;
            t.d = d;

            return rotate.call(this,w);
         }
      }();
      CanvasRenderingContext2D.prototype.translate = function() {
         var translate = CanvasRenderingContext2D.prototype.translate;
         return function(x,y) {
            if (!this._t2stack)
               this._t2stack = [{a:1,b:0,c:0,d:1,e:0,f:0}];
            var t = this._t2stack[this._t2stack.length-1];
            t.e += x*t.a + y*t.c;
            t.f += x*t.b + y*t.d;
            return translate.call(this,x,y);
         }
      }();
   }
}