2016 Update

Task/Death-Star/Q/death-star-1.q

@@ -0,0 +1,42 @@
+/ https://en.wikipedia.org/wiki/BMP_file_format
+/ BITMAPINFOHEADER / RGB24
+
+/ generate a header
+
+genheader:{[w;h]
+   0x424d, "x"$(f2i4[54+4*h*w],0,0,0,0,54,0,0,0,40,0,0,0,
+                f2i4[h],f2i4[w],1,0,24,0,0,0,0,0,
+                f2i4[h*((w*3)+((w*3)mod 4))],
+                19,11,0,0,19,11,0,0,0,0,0,0,0,0,0,0)};
+
+/ generate a raster line at a vertical position
+
+genrow:{[w;y;fcn]
+    row:enlist 0i;xx:0i;do[w;row,:fcn[xx;y];xx+:1i];row,:((w mod 4)#0i);1_row};
+
+/ generate a bitmap
+
+genbitmap:{[w;h;fcn]
+    ary:enlist 0i;yy:0i;do[h;ary,:genrow[w;yy;fcn];yy+:1i];"x"$1_ary};
+
+/ deal with endianness
+/ might need to reverse last line if host computer is not a PC
+
+f2i4:{[x] r:x;
+  s0:r mod 256;r-:s0; r%:256;
+  s1:r mod 256;r-:s1; r%:256;
+  s2:r mod 256;r-:s2; r%:256;
+  s3:r mod 256;
+  "h"$(s0,s1,s2,s3)}
+
+/ compose and write a file
+
+writebmp:{[w;h;fcn;fn]
+    fn 1: (genheader[h;w],genbitmap[w;h;fcn])};
+
+/ / usage example:
+/ w:400;
+/ h:300;
+/ fcn:{x0:x-w%2;y0:y-h%2;r:175;$[(r*r)>((x0*x0)+(y0*y0));(0;0;255);(0;255;0)]};
+/ fn:`:demo.bmp;
+/ writebmp[w;h;fcn;fn];

Task/Death-Star/Q/death-star-2.q

@@ -0,0 +1,38 @@
+w:400; h:300; r:150; l:-0.5 0.7 0.5
+sqrt0:{$[x>0;sqrt x;0]};
+
+/ get x,y,z position of point on sphere given x,y,r
+
+z:{[x;y;r]sqrt0((r*r)-((x*x)+(y*y)))};
+
+/ get diffused light at point on sphere
+
+is:{[x;y;r]
+   z0:z[x;y;r];
+   s:(x;y;z0)%r;
+   $[z0>0;i:0.5*1+(+/)(s*l);i:0];
+   i};
+
+/ get pixel value at given image position
+
+fcn:{[xpx;ypx]
+   x:xpx-w%2;
+   y:ypx-h%2;
+   z1:z[x;y;r];
+   x2:x+190;
+   z2:170-z[x2;y;r];
+   $[(r*r)<((x*x)+(y*y));
+      $[y>-50;
+          i:3#0;
+          i:200 100 50];
+      $[z2>z1;
+         i:3#is[x;y;r]*140;
+         i:3#is[(-1*x2);(-1*y);r]*120]
+   ];
+   "i"$i};
+
+/ do it ...
+
+\l bmp.q
+fn:`:demo.bmp;
+writebmp[w;h;fcn;fn];