an improved illumination model for shaded display

Toaccuratelyrenderatwo-dimensionalimageofathree-dimensionalscene,globalilluminationinformationthataffectstheintensityofeachpixeloftheimagemustbeknownatthetimetheintensityiscalculated.Inasimplifiedform,thisinformationisstoredinatreeof"rays&quo