add:   if (this.startTime == this.endTime) return; 
context:     redrawOverlayOnly: function () {        with (this.frontBuffer.getContext("2d")) {            globalCompositeOperation = "copy";            drawImage(this.backBuffer, 0, 0);        }        var doDrawOverlay = false;        with (this.overlayBuffer.getContext("2d")) {            clearRect(0, 0, this.overlayBuffer.width, this.overlayBuffer.height);            if (this.selectionCursorTime || (this.selectionStartTime && this.selectionEndTime)) {                var spixel, epixel;                var pps = (this.frontBuffer.width / (this.endTime - this.startTime + this.offsetTime));                if (this.selectionCursorTime) {                    spixel = Math.round((this.selectionCursorTime-this.startTime) * pps);                    epixel = spixel + 1;                } else if (this.selectionStartTime && this.selectionEndTime) {                    spixel = Math.round((this.selectionStartTime-this.startTime) * pps);                    epixel = Math.round((this.selectionEndTime-this.startTime) * pps);                }                globalCompositeOperation = "over";                fillStyle = this.selectionColor;                fillRect(spixel, 0, epixel - spixel, this.frontBuffer.height);                doDrawOverlay = true;            }            if ((this.cursorType != "none") && this.cursorTime != null && this.cursorValue != null) {                globalCompositeOperation = "over";                strokeStyle = this.cursorColor;                var cw = this.frontBuffer.width;                var ch = this.frontBuffer.height;                var v;                v = ch - Math.round((this.cursorValue - this.yOffset) * this.yScale);                beginPath();                moveTo(  -0.5, v+0.5);                lineTo(cw+0.5, v+0.5);                stroke();                v = Math.round((this.cursorTime-this.startTime) * cw/(this.endTime - this.startTime + this.offsetTime));                beginPath();                moveTo(v+0.5,   -0.5);                lineTo(v+0.5, ch+0.5);                stroke();                doDrawOverlay = true;            }        }        if (doDrawOverlay) {            with (this.frontBuffer.getContext("2d")) {                globalCompositeOperation = "over";                drawImage(this.overlayBuffer, 0, 0);            }        }    },
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2007_temp/2007/9421/1114e91ece14d46754cce7312c20dd171c1d642f/GraphCanvas.js/buggy/webtools/new-graph/js/GraphCanvas.js