public void offset(float dx, float dy) {
        left += dx;
        top += dy;
        right += dx;
        bottom += dy;
    }
Offset the viewport by adding dx to its left and right coordinates, and adding dy to its top and bottom
coordinates.

@param dx The amount to add to the viewport's left and right coordinates
@param dy The amount to add to the viewport's top and bottom coordinates
hellocharts-library/src/lecho/lib/hellocharts/model/Viewport.java