@Override
    public void draw(Canvas canvas) {
        // softwareBitmap can be null if chart is rendered in layout editor. In that case use default canvas and not
        // softwareCanvas.
        final Canvas drawCanvas;
        if (null != softwareBitmap) {
            drawCanvas = softwareCanvas;
            drawCanvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
        } else {
            drawCanvas = canvas;
        }

        drawSlices(drawCanvas);
        drawSeparationLines(drawCanvas);
        if (hasCenterCircle) {
            drawCenterCircle(drawCanvas);
        }
        drawLabels(drawCanvas);

        if (null != softwareBitmap) {
            canvas.drawBitmap(softwareBitmap, 0, 0, null);
        }
    }
Default renderer for PieChart. PieChart doesn't use viewport concept so it a little different than others chart
types.
hellocharts-library/src/lecho/lib/hellocharts/renderer/PieChartRenderer.java