Fix more reflection issues

Since b393050, surface normals were calculated incorrectly because blocking cells were detected as blocking only if they were within the heading of the scout process (see that commit for terminology). This had been true even before that commit but it had had less visible effects because both processes would traverse their neighbours in the same order, which the initial heading approximation code (direction_to_map, removed in this commit) had worked better with.

This commit fixes this by separating information about blocking entirely from information about current heading, as it should be. This fixes a few prism-type saves such as id:1188302, but is also not entirely backwards-compatible, for all saves that are considered broken as far as normal calculation code is concerned (e.g. the surfaces are not long enough or are wobbly) will now be broken differently from before. This affects for example many coalescing laser-type saves such as id:482187 that rely on very specific arrangements of very few particles of reflective material behaving as perfect 45deg mirrors.

src/simulation/Simulation.cpp

@@ -1735,35 +1735,6 @@ void Simulation::photoelectric_effect(int nx, int ny)//create sparks from PHOT w
 	}
 }
 
-unsigned Simulation::direction_to_map(float dx, float dy, int t)
-{
-	// TODO:
-	// Adding extra directions causes some inaccuracies.
-	// Not adding them causes problems with some diagonal surfaces (photons absorbed instead of reflected).
-	// For now, don't add them.
-	// Solution may involve more intelligent setting of initial i0 value in find_next_boundary?
-	// or rewriting normal/boundary finding code
-
-	return (dx >= 0) |
-	       (((dx + dy) >= 0) << 1) |     /*  567  */
-	       ((dy >= 0) << 2) |            /*  4+0  */
-	       (((dy - dx) >= 0) << 3) |     /*  321  */
-	       ((dx <= 0) << 4) |
-	       (((dx + dy) <= 0) << 5) |
-	       ((dy <= 0) << 6) |
-	       (((dy - dx) <= 0) << 7);
-	/*
-	return (dx >= -0.001) |
-	       (((dx + dy) >= -0.001) << 1) |     //  567
-	       ((dy >= -0.001) << 2) |            //  4+0
-	       (((dy - dx) >= -0.001) << 3) |     //  321
-	       ((dx <= 0.001) << 4) |
-	       (((dx + dy) <= 0.001) << 5) |
-	       ((dy <= 0.001) << 6) |
-	       (((dy - dx) <= 0.001) << 7);
-	}*/
-}
-
 int Simulation::is_blocking(int t, int x, int y)
 {
 	if (t & REFRACT) {
@@ -1805,15 +1776,15 @@ int Simulation::find_next_boundary(int pt, int *x, int *y, int dm, int *em, bool
 	unsigned int mask = 0;
 	for (int i = 0; i < 8; ++i)
 	{
-		if ((dm & (1U << i)) && is_blocking(pt, *x + dx[i], *y + dy[i]))
+		if (is_blocking(pt, *x + dx[i], *y + dy[i]))
 		{
 			mask |= (1U << i);
 		}
 	}
 	for (int i = 0; i < 8; ++i)
 	{
 		int n = (i + (reverse ? 1 : -1)) & 7;
-		if (((mask & (1U << i))) && !(mask & (1U << n)))
+		if (((dm & mask & (1U << i))) && !(mask & (1U << n)))
 		{
 			*x += dx[i];
 			*y += dy[i];
@@ -1838,8 +1809,8 @@ int Simulation::get_normal(int pt, int x, int y, float dx, float dy, float *nx,
 	if (!is_boundary(pt, x, y))
 		return 0;
 
-	ldm = direction_to_map(-dy, dx, pt);
-	rdm = direction_to_map(dy, -dx, pt);
+	ldm = 0xFF;
+	rdm = 0xFF;
 	lx = rx = x;
 	ly = ry = y;
 	lv = rv = 1;
@@ -3076,10 +3047,10 @@ void Simulation::UpdateParticles(int start, int end)
 							}
 							nn = GLASS_IOR - GLASS_DISP*(r-30)/30.0f;
 							nn *= nn;
-							nrx = -nrx;
-							nry = -nry;
-							if (rt_glas && !lt_glas)
-								nn = 1.0f/nn;
+							auto enter = rt_glas && !lt_glas;
+							nrx = enter ? -nrx : nrx;
+							nry = enter ? -nry : nry;
+							nn = enter ? 1.0f/nn : nn;
 							ct1 = parts[i].vx*nrx + parts[i].vy*nry;
 							ct2 = 1.0f - (nn*nn)*(1.0f-(ct1*ct1));
 							if (ct2 < 0.0f) {

src/simulation/Simulation.h

@@ -133,7 +133,6 @@ class Simulation
 	int is_boundary(int pt, int x, int y);
 	int find_next_boundary(int pt, int *x, int *y, int dm, int *em, bool reverse);
 	void photoelectric_effect(int nx, int ny);
-	unsigned direction_to_map(float dx, float dy, int t);
 	int do_move(int i, int x, int y, float nxf, float nyf);
 	bool move(int i, int x, int y, float nxf, float nyf);
 	int try_move(int i, int x, int y, int nx, int ny);