shithub: puzzles

Pattern: randomise rounding bias in generate(). Now, with an odd grid size, we choose the posterisation threshold so that half the time it delivers ceil(n/2) black squares and half the time it delivers floor(n/2). Previously it only did the former, which meant that asking Pattern to generate a 1x1 puzzle (with the bug in the previous commit fixed) would always generate the one with a single black square, and never the one with a single white square. Both are trivial to solve, of course, but it seemed inelegant! No change to the number of black squares in the puzzle solution can constitute a spoiler for the player, of course, because that number is trivial to determine without doing any difficult reasoning, just by adding up all the clues in one dimension.

--- a/pattern.c

+++ b/pattern.c

@@ -308,7 +308,18 @@

     fgrid2 = snewn(w*h, float);

     memcpy(fgrid2, fgrid, w*h*sizeof(float));

     qsort(fgrid2, w*h, sizeof(float), float_compare);

-    threshold = fgrid2[w*h/2];

+    /* Choose a threshold that makes half the pixels black. In case of

+     * an odd number of pixels, select randomly between just under and

+     * just over half. */

+    {

+        int index = w * h / 2;

+        if (w & h & 1)

+            index += random_upto(rs, 2);

+        if (index < w*h)

+            threshold = fgrid2[index];

+        else

+            threshold = fgrid2[w*h-1] + 1;

+    }

     sfree(fgrid2);

     for (i = 0; i < h; i++) {