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| BACK TO TUTORIAL/CRITIQUE INDEX. | |
| 01: TUTORIALS | |
| CAST SHADOWS FROM A SINGLE POINT LIGHT SOURCE FALLING ON AN ADJACENT OBJECT.
HERE'S A LITTLE DIAGRAM SHOWING SOME PRINCIPLES OF SHADOWS CAST ONTO ANOTHER OBJECT. THERE'S A LOTTA LINES, BUT HOPEFULLY THIS MAKES A LITTLE BIT OF SENSE. FOR CLARITY, I'VE OMITTED THE CONSTRUCTION LINES FOR THE CUBE, AND I'VE ONLY CONSTRUCTED THE SHADOW FOR THE CUBE ON THE LEFT. THIS IS MOSTLY THE SAME AS THE PREVIOUS DIAGRAM DEALING WITH SHADOWS. THE DIFFERENCE HERE IS THAT THE SHADOW FALLS ON THE VERTICAL SURFACE OF THE ADJACENT CUBE. AGAIN FOR SIMPLICITY, I'VE MADE THE CUBES PARALLEL TO EACH OTHER, SO THAT THE FACES OF ONE CUBE ARE PARALLEL TO THE OTHER. THE KEY HERE IS THAT THE VERTICAL LINE "a-b" OF THE LEFT HAND CUBE CREATES THE SHADOW LINE FROM POINT "b". (THE ONE ALONG THE GROUND, FOLLOWING "b-bb".) IT STOPS AT THE BASE OF THE SECOND CUBE. NOW IF YOU IMAGINE LINE "a-b" AS A STICK IN THE GROUND, IT WOULD CAST THE SHADOW "aa-bb" ON THE SECOND CUBE. THE POINT "aa" IS THE CRITICAL ONE, FROM WHICH YOU CAN CONSTRUCT THE REST OF THE SHADOW - THE HEIGHT OF "aa" COMES FROM A LINE ORIGINATING AT THE LIGHT SOURCE AND PASSING THROUGH POINT "a". BECAUSE THE TOP EDGE OF THE SHADOW IS CAUSED BY THE TOP EDGE OF THE LEFT HAND CUBE, IT GOES TO THE LEFT HAND V.P. RATHER THAN THE LIGHT OR SHADOW V.P. (IN GENERAL, SHADOW EDGES CAUSED BY VERTICALS GO TO THE SHADOW V.P., AND SHADOW EDGES CAUSED BY HORIZONTAL EDGES OF THE CUBE GO TO THE "NORMAL" LEFT OR RIGHT V.P.) THE SHORT DIAGONAL EDGE OF THE SHADOW CAST ON THE FACE OF THE CUBE STARTS AT THE BOTTOM OF THE FACE, WHERE IT MEETS THE GROUND, AND THEN TRAVELS UP TO THE POINT "aa" YOU DETERMINED EARLIER. |
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