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Apply the rotation in Penrose grid descriptions by rotating in the
4-vector representation, rather than mucking about with sines and
cosines after grid generation. _Should_ make no difference in the
generated grids (there's a theoretical risk of an unlucky rounding
error just about managing to push some point in or out of bounds, but
I think it's vanishingly small), but simplifies the coordinate-
flattening procedure, and in particular increases its chance of
getting vertical lines actually vertical.

(Prior to this change, the game ID
10x10t12:G2554,-31,108_a3b12h0a212a3d102b2a23a2e3b01b0a2c2a0c0 was
generating a not-quite-vertical edge at top left, in the Java port but
not on Linux; I suspect differences in sin and cos as the cause of the
discrepancy. With the rotation done like this, the points'
x-coordinates are now computed without reference to their
y-coordinates.)

[originally from svn r9168]

--- a/grid.c

+++ b/grid.c

@@ -2472,7 +2472,6 @@

 typedef struct setface_ctx

 {

     int xmin, xmax, ymin, ymax;

-    int aoff;

     grid *g;

     tree234 *points;

@@ -2488,8 +2487,6 @@

     setface_ctx *sf_ctx = (setface_ctx *)state->ctx;

     int i;

     int xs[4], ys[4];

-    double cosa = cos(sf_ctx->aoff * PI / 180.0);

-    double sina = sin(sf_ctx->aoff * PI / 180.0);

     if (depth < state->max_depth) return 0;

 #ifdef DEBUG_PENROSE

@@ -2499,8 +2496,8 @@

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

         double tx = v_x(vs, i), ty = v_y(vs, i);

-        xs[i] = (int)round_int_nearest_away( tx*cosa + ty*sina);

-        ys[i] = (int)round_int_nearest_away(-tx*sina + ty*cosa);

+        xs[i] = (int)round_int_nearest_away(tx);

+        ys[i] = (int)round_int_nearest_away(ty);

         if (xs[i] < sf_ctx->xmin || xs[i] > sf_ctx->xmax) return 0;

         if (ys[i] < sf_ctx->ymin || ys[i] > sf_ctx->ymax) return 0;

@@ -2602,7 +2599,7 @@

 static grid *grid_new_penrose(int width, int height, int which, char *desc)

 {

     int max_faces, max_dots, tilesize = PENROSE_TILESIZE;

-    int xsz, ysz, xoff, yoff;

+    int xsz, ysz, xoff, yoff, aoff;

     double rradius;

     tree234 *points;

@@ -2635,7 +2632,7 @@

     sf_ctx.points = points;

     if (desc != NULL) {

-        if (sscanf(desc, "G%d,%d,%d", &xoff, &yoff, &sf_ctx.aoff) != 3)

+        if (sscanf(desc, "G%d,%d,%d", &xoff, &yoff, &aoff) != 3)

             assert(!"Invalid grid description.");

     } else {

         xoff = yoff = 0;

@@ -2654,7 +2651,7 @@

     debug(("penrose: x range (%f --> %f), y range (%f --> %f)",

            sf_ctx.xmin, sf_ctx.xmax, sf_ctx.ymin, sf_ctx.ymax));

-    penrose(&ps, which);

+    penrose(&ps, which, aoff);

     freetree234(points);

     assert(g->num_faces <= max_faces);

--- a/penrose.c

+++ b/penrose.c

@@ -434,7 +434,7 @@

  * (later mail: this is an overestimate by about 5%)

  */

-int penrose(penrose_state *state, int which)

+int penrose(penrose_state *state, int which, int angle)

 {

     vector vo = v_origin();

     vector vb = v_origin();

@@ -443,6 +443,9 @@

     vo = v_shrinkphi(v_shrinkphi(vo));

     vb.b = state->start_size;

+

+    vo = v_rotate(vo, angle);

+    vb = v_rotate(vb, angle);

     if (which == PENROSE_P2)

         return penrose_p2_large(state, 0, 1, vo, vb);

--- a/penrose.h

+++ b/penrose.h

@@ -42,7 +42,7 @@

 enum { PENROSE_P2, PENROSE_P3 };

-extern int penrose(penrose_state *state, int which);

+extern int penrose(penrose_state *state, int which, int angle);

 /* Returns the side-length of a penrose tile at recursion level

  * gen, given a starting side length. */