cheap_darken            'light' effect helper functions
geom_oblicubes          Draw 2D/3D cubes with ggplot2
geom_oblicuboids        Draw 2D/3D cuboids with ggplot2
oblicubesGrob           Render 2D/3D cubes via an oblique projection
oblicuboidsGrob         Render 2D/3D cuboids via an oblique projection
xyz_heightmap           Calculate x,y,z coordinates from a height
                        matrix
