code: function StepCanvas(canvas, stepParams, padding) {
          this.canvas     = canvas;
          this.stepParams = stepParams;
          this.padding    = this.getPadding(padding);
  
          // Convert to a cartesian coordinate system with axes from 0 to 1
          var ctx = this.canvas.getContext("2d"),
              p = this.padding;
  
          ctx.scale(canvas.width * (1 - p[1] - p[3]), -canvas.height * (1 - p[0] - p[2]));
          ctx.translate(p[3] / (1 - p[1] - p[3]), (-1 - p[0] / (1 - p[0] - p[2])));
      }
docs: StepCanvas object constructor
  
  @param {Element} canvas Inline editor <canvas> element
  @param {StepParameters} stepParams Associated StepParameters object
  @param {number|Array.number} padding Element padding