From 0f652dc0a82632e033d940c19e38b7df68b78180 Mon Sep 17 00:00:00 2001 From: Alina Lenk Date: Sat, 5 Mar 2022 22:41:54 +0100 Subject: [PATCH] Split map_colatitude() responsibilities into separate functions See osdn #44037 Also makes singlepole torus maps possible. Signed-off-by: Alina Lenk --- server/generator/mapgen_topology.c | 196 +++++++++++++++++++---------- server/settings.c | 3 +- 2 files changed, 128 insertions(+), 71 deletions(-) diff --git a/server/generator/mapgen_topology.c b/server/generator/mapgen_topology.c index a87c1dda95..d83015dc70 100644 --- a/server/generator/mapgen_topology.c +++ b/server/generator/mapgen_topology.c @@ -28,86 +28,55 @@ int ice_base_colatitude = 0 ; /************************************************************************//** - Returns the colatitude of this map position. This is a value in the - range of 0 to MAX_COLATITUDE (inclusive). - This function is wanted to concentrate the topology information - all generator code has to use colatitude and others topology safe - functions instead (x,y) coordinate to place terrains - colatitude is 0 at poles and MAX_COLATITUDE at equator + Returns the relative southness of this map position. + This is a value in the range of [0.0, 1.0]. + This function handles all topology-specific information so that all + other generator code can work in a topology-agnostic way. + + relative southness is 0.0 at the northernmost point and 1.0 at the + southernmost point on the map. These may or may not be polar regions + (depending on various generator settings). + On a map representing only a northern hemisphere, southness directly + corresponds to colatitude, going from 0.0 at the pole to 1.0 at the + equator. + On a map representing only a southern hemisphere, it directly + corrsponds to (negative) latitude, going from 0.0 at the equator to + 1.0 at the pole. + + See also map_signed_latitude ****************************************************************************/ -int map_colatitude(const struct tile *ptile) +static double map_relative_southness(const struct tile *ptile) { - double x, y; int tile_x, tile_y; + double x, y, toroid_rel_colatitude; + bool toroid_flipped; - fc_assert_ret_val(ptile != NULL, MAX_COLATITUDE / 2); - - if (wld.map.server.alltemperate) { - /* An all-temperate map has "average" temperature everywhere. - * - * TODO: perhaps there should be a random temperature variation. */ - return MAX_COLATITUDE / 2; - } - + /* TODO: What should the fallback value be? + * Since this is not public API, it shouldn't matter anyway. */ + fc_assert_ret_val(ptile != NULL, 0.5); index_to_map_pos(&tile_x, &tile_y, tile_index(ptile)); do_in_natural_pos(ntl_x, ntl_y, tile_x, tile_y) { - if (wld.map.server.single_pole) { - if (!current_topo_has_flag(TF_WRAPY)) { - /* Partial planetary map. A polar zone is placed - * at the top and the equator is at the bottom. */ - return MAX_COLATITUDE * ntl_y / (NATURAL_HEIGHT - 1); - } - if (!current_topo_has_flag(TF_WRAPX)) { - return MAX_COLATITUDE * ntl_x / (NATURAL_WIDTH -1); - } - } - - /* Otherwise a wrapping map is assumed to be a global planetary map. */ - - /* we fold the map to get the base symmetries - * - * ...... - * :c__c: - * :____: - * :____: - * :c__c: - * ...... - * - * C are the corners. In all cases the 4 corners have equal temperature. - * So we fold the map over in both directions and determine - * x and y vars in the range [0.0, 1.0]. - * - * ...>x - * :C_ - * :__ - * V - * y - * - * And now this is what we have - just one-quarter of the map. - */ - x = ((ntl_x > (NATURAL_WIDTH / 2 - 1) - ? NATURAL_WIDTH - 1.0 - (double)ntl_x - : (double)ntl_x) - / (NATURAL_WIDTH / 2 - 1)); - y = ((ntl_y > (NATURAL_HEIGHT / 2 - 1) - ? NATURAL_HEIGHT - 1.0 - (double)ntl_y - : (double)ntl_y) - / (NATURAL_HEIGHT / 2 - 1)); + /* Compute natural coordinates relative to world size. + * x and y are in the range [0.0, 1.0] */ + x = (double)ntl_x / (NATURAL_WIDTH - 1); + y = (double)ntl_y / (NATURAL_HEIGHT - 1); } do_in_natural_pos_end; if (!current_topo_has_flag(TF_WRAPY)) { - /* In an Earth-like topology the polar zones are at north and south. + /* In an Earth-like topology, north and south are at the top and + * bottom of the map. * This is equivalent to a Mercator projection. */ - return MAX_COLATITUDE * y; + return y; } if (!current_topo_has_flag(TF_WRAPX) && current_topo_has_flag(TF_WRAPY)) { - /* In a Uranus-like topology the polar zones are at east and west. + /* In a Uranus-like topology, north and south are at the left and + * right side of the map. * This isn't really the way Uranus is; it's the way Earth would look * if you tilted your head sideways. It's still a Mercator * projection. */ - return MAX_COLATITUDE * x; + return x; } /* Otherwise we have a torus topology. We set it up as an approximation @@ -129,14 +98,19 @@ int map_colatitude(const struct tile *ptile) * '''''''' */ - /* Remember that we've already folded the map into fourths: + /* First we will fold the map into fourths: * * .... * :\ N * : \ * :S \ * - * Now flip it along the X direction to get this: + * and renormalize x and y to go from 0.0 to 1.0 again. + */ + x = 2.0 * (x > 0.5 ? 1.0 - x : x); + y = 2.0 * (y > 0.5 ? 1.0 - y : y); + + /* Now flip it along the X direction to get this: * * .... * :N / @@ -145,7 +119,7 @@ int map_colatitude(const struct tile *ptile) */ x = 1.0 - x; - /* Since the north and south poles are equivalent, we can fold along the + /* To simplify the following computation, we can fold along the * diagonal. This leaves us with 1/8 of the map * * ..... @@ -153,13 +127,20 @@ int map_colatitude(const struct tile *ptile) * : / * :/ * - * where P is the polar regions and / is the equator. */ + * where P is the polar regions and / is the equator. + * We must remember which hemisphere we are on for later. */ if (x + y > 1.0) { + /* This actually reflects the bottom-right half about the center point, + * rather than about the diagonal, but that makes no difference. */ x = 1.0 - x; y = 1.0 - y; + toroid_flipped = TRUE; + } else { + toroid_flipped = FALSE; } - /* This projection makes poles with a shape of a quarter-circle along + /* toroid_rel_colatitude is 0.0 at the poles and 1.0 at the equator. + * This projection makes poles with a shape of a quarter-circle along * "P" and the equator as a straight line along "/". * * The formula is @@ -193,9 +174,86 @@ int map_colatitude(const struct tile *ptile) * * See OSDN#43665, as well as the original discussion (via newsreader) at * news://news.gmane.io/gmane.games.freeciv.devel/42648 */ - return MAX_COLATITUDE * (1.5 * (x * x * y + x * y * y) + toroid_rel_colatitude = (1.5 * (x * x * y + x * y * y) - 0.5 * (x * x * x + y * y * y) + 1.5 * (x * x + y * y)); + + /* Finally, convert from colatitude to latitude and add hemisphere + * information back in: + * - if we did not flip along the diagonal before, we are in the + * northern hemisphere, with relative latitude in [0.0,0.5] + * - if we _did_ flip, we are in the southern hemisphere, with + * relative latitude in [0.5,1.0] + */ + return ((toroid_flipped + ? 2.0 - (toroid_rel_colatitude) + : (toroid_rel_colatitude)) + / 2.0); +} + +/************************************************************************//** + Returns the latitude of this map position. This is a value in the + range of -MAX_COLATITUDE to MAX_COLATITUDE (inclusive). + + latitude reaches MAX_COLATITUDE in the northern polar region, + reaches -MAX_COLATITUDE in the southern polar region, + and is around 0 in the tropics. + + See also map_colatitude +****************************************************************************/ +static int map_signed_latitude(const struct tile *ptile) +{ + int north_latitude, south_latitude; + double southness; + + /* TODO: Move upper and lower latitude bounds to server settings + * (replacing alltemperate and singlepole). */ + if (wld.map.server.alltemperate) { + /* An all-temperate map has "average" temperature everywhere. */ + north_latitude = south_latitude = MAX_COLATITUDE / 2; + } else if (wld.map.server.single_pole) { + /* Partial planetary map. A polar zone is placed at the north end + * and a tropical zone at the south end. */ + north_latitude = MAX_COLATITUDE; + south_latitude = 0; + } else { + /* Full latitude range */ + north_latitude = MAX_COLATITUDE; + south_latitude = -MAX_COLATITUDE; + } + + if (north_latitude == south_latitude) { + /* Single-latitude / all-temperate map; no need to examine tile. */ + return south_latitude; + } + + fc_assert_ret_val(ptile != NULL, (north_latitude + south_latitude) / 2); + + southness = map_relative_southness(ptile); + + /* Linear interpolation between maximum and minimum latitude. + * Truncate / round towards zero so northern and southern hemisphere + * are symmetrical when south_latitude = -north_latitude. */ + return north_latitude * (1.0 - southness) + south_latitude * southness; +} + +/************************************************************************//** + Returns the colatitude of this map position. This is a value in the + range of 0 to MAX_COLATITUDE (inclusive). + This function is wanted to concentrate the topology information + all generator code has to use colatitude and others topology safe + functions instead (x,y) coordinate to place terrains + colatitude is 0 at poles and MAX_COLATITUDE at equator +****************************************************************************/ +int map_colatitude(const struct tile *ptile) +{ + int latitude; + fc_assert_ret_val(ptile != NULL, MAX_COLATITUDE / 2); + + latitude = map_signed_latitude(ptile); + latitude = MAX(latitude, -latitude); + + return MAX_COLATITUDE - latitude; } /************************************************************************//** diff --git a/server/settings.c b/server/settings.c index 10ed03375f..e5da74ea8f 100644 --- a/server/settings.c +++ b/server/settings.c @@ -1592,8 +1592,7 @@ static struct setting settings[] = { ALLOW_NONE, ALLOW_BASIC, N_("Whether there's just one pole generated"), N_("If this setting is enabled, only one side of the map will have " - "a pole. This setting has no effect if the map wraps both " - "directions."), NULL, NULL, MAP_DEFAULT_SINGLE_POLE) + "a pole."), NULL, NULL, MAP_DEFAULT_SINGLE_POLE) GEN_BOOL("alltemperate", wld.map.server.alltemperate, SSET_MAP_GEN, SSET_GEOLOGY, SSET_RARE, ALLOW_NONE, ALLOW_BASIC, -- 2.17.1