Data commit

Task/Draw-a-sphere/XPL0/draw-a-sphere.xpl0

@@ -0,0 +1,18 @@
+include c:\cxpl\codes;          \intrinsic 'code' declarations
+def     R=100, R2=R*R;          \radius, in pixels; radius squared
+def     X0=640/2, Y0=480/2;     \coordinates of center of screen
+int     X, Y, Z, C, D2;         \coords, color, distance from center squared
+[SetVid($112);                  \set 640x480x24 graphics mode
+for Y:= -R to +R do             \for all the coordinates near the circle
+    for X:= -R to +R do         \ which is under the sphere
+        [D2:= X*X + Y*Y;
+        C:= 0;                  \default color is black
+        if D2 <= R2 then        \coordinate is inside circle under sphere
+            [Z:= sqrt(R2-D2);   \height of point on surface of sphere above X,Y
+            C:= Z-(X+Y)/2+130;  \color is proportional; offset X and Y, and
+            ];                  \ shift color to upper limit of its range
+        Point(X+X0, Y+Y0, C<<8+C); \green + blue = cyan
+       ];
+repeat until KeyHit;            \wait for keystroke
+SetVid($03);                    \restore normal text mode
+]