src/shared/geom.pas

   1 (* Copyright (C)  Doom 2D: Forever Developers
   2  *
   3  * This program is free software: you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation, version 3 of the License ONLY.
   6  *
   7  * This program is distributed in the hope that it will be useful,
   8  * but WITHOUT ANY WARRANTY; without even the implied warranty of
   9  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  10  * GNU General Public License for more details.
  11  *
  12  * You should have received a copy of the GNU General Public License
  13  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  14  *)
  15 {$INCLUDE a_modes.inc}
  16 // some geometry utilities
  17 unit geom;
  18
  19 interface
  20
  21
  22 // do line clipping; returns `false` if line is outside of the box
  23 function clipLine (var x0, y0, x1, y1: Single; xmin, ymin, xmax, ymax: Single): Boolean;
  24
  25 // returns `true` if there is an intersection (if starting point is inside the box, it counts as intersection)
  26 function lineAABBIntersects (x0, y0, x1, y1: Integer; bx, by, bw, bh: Integer): Boolean;
  27
  28 // you are not supposed to understand this
  29 // returns `true` if there is an intersection, and enter coords
  30 // enter coords will be equal to (x0, y0) if starting point is inside the box
  31 // if result is `false`, `inx` and `iny` are undefined
  32 function lineAABBIntersects (x0, y0, x1, y1: Integer; bx, by, bw, bh: Integer; out inx, iny: Integer): Boolean;
  33
  34 type
  35   TSweepEdge = (None, Top, Right, Bottom, Left);
  36   PSweepEdge = ^TSweepEdge;
  37
  38 // sweep two AABB's to see if and when they are overlapping
  39 // returns `true` if collision was detected (but boxes aren't overlap)
  40 // `u1` and `u1` has no sense if no collision was detected (`hitx` and `hity` either)
  41 // u0 = normalized time of first collision (i.e. collision starts at myMove*u0)
  42 // u1 = normalized time of second collision (i.e. collision stops after myMove*u1)
  43 // hitedge for `it`: it will probably be `None` if no collision was detected, but it is not guaranteed
  44 // enter/exit coords will form non-intersecting configuration (i.e. will be before/after the actual collision)
  45 // but beware of floating point inexactness; `sweepAABB()` will try to (crudely) compensate for it
  46 // while calculating `hitx` and `hity`.
  47 {
  48 function sweepAABB (mex0, mey0, mew, meh: Integer; medx, medy: Integer; itx0, ity0, itw, ith: Integer;
  49                     u0: PSingle=nil; hitedge: PSweepEdge=nil; u1: PSingle=nil;
  50                     hitx: PInteger=nil; hity: PInteger=nil): Boolean;
  51 }
  52 function sweepAABB (mex0, mey0, mew, meh: Integer; medx, medy: Integer; itx0, ity0, itw, ith: Integer;
  53                     out u0: Single): Boolean;
  54
  55 function distanceSq (x0, y0, x1, y1: Integer): Integer; inline;
  56
  57
  58 implementation
  59
  60
  61 // ////////////////////////////////////////////////////////////////////////// //
  62 function distanceSq (x0, y0, x1, y1: Integer): Integer; inline; begin result := (x1-x0)*(x1-x0)+(y1-y0)*(y1-y0); end;
  63
  64
  65 // ////////////////////////////////////////////////////////////////////////// //
  66 function clipLine (var x0, y0, x1, y1: Single; xmin, ymin, xmax, ymax: Single): Boolean;
  67 const
  68   Inside = 0;
  69   Left = 1;
  70   Right = 2;
  71   Bottom = 4;
  72   Top = 8;
  73
  74   function xcode (x, y: Single): Byte; inline;
  75   begin
  76     result := Inside;
  77     if (x < xmin) then result := result or Left else if (x > xmax) then result := result or Right;
  78     if (y < ymin) then result := result or Bottom else if (y > ymax) then result := result or Top;
  79   end;
  80
  81 var
  82   outcode0, outcode1, outcodeOut: Byte;
  83   x: Single = 0;
  84   y: Single = 0;
  85 begin
  86   result := false; // accept
  87   outcode0 := xcode(x0, y0);
  88   outcode1 := xcode(x1, y1);
  89   while true do
  90   begin
  91     if ((outcode0 or outcode1) = 0) then begin result := true; exit; end; // accept
  92     if ((outcode0 and outcode1) <> 0) then exit; // reject
  93     outcodeOut := outcode0;
  94     if (outcodeOut = 0) then outcodeOut := outcode1;
  95     if ((outcodeOut and Top) <> 0) then
  96     begin
  97       x := x0+(x1-x0)*(ymax-y0)/(y1-y0);
  98       y := ymax;
  99     end
 100     else if ((outcodeOut and Bottom) <> 0) then
 101     begin
 102       x := x0+(x1-x0)*(ymin-y0)/(y1-y0);
 103       y := ymin;
 104     end
 105     else if ((outcodeOut and Right) <> 0) then
 106     begin
 107       y := y0+(y1-y0)*(xmax-x0)/(x1-x0);
 108       x := xmax;
 109     end
 110     else if ((outcodeOut and Left) <> 0) then
 111     begin
 112       y := y0+(y1-y0)*(xmin-x0)/(x1-x0);
 113       x := xmin;
 114     end;
 115     if (outcodeOut = outcode0) then
 116     begin
 117       x0 := x;
 118       y0 := y;
 119       outcode0 := xcode(x0, y0);
 120     end
 121     else
 122     begin
 123       x1 := x;
 124       y1 := y;
 125       outcode1 := xcode(x1, y1);
 126     end;
 127   end;
 128 end;
 129
 130
 131 // returns `true` if there is an intersection (if starting point is inside the box, it counts as intersection)
 132 function lineAABBIntersects (x0, y0, x1, y1: Integer; bx, by, bw, bh: Integer): Boolean;
 133 var
 134   sx0, sy0, sx1, sy1: Single;
 135 begin
 136   result := false;
 137   if (bw < 1) or (bh < 1) then exit;
 138   if (x0 >= bx) and (y0 >= by) and (x0 < bx+bw) and (y0 < by+bh) then begin result := true; exit; end;
 139   sx0 := x0; sy0 := y0;
 140   sx1 := x1; sy1 := y1;
 141   result := clipLine(sx0, sy0, sx1, sy1, bx, by, bx+bw-1, by+bh-1);
 142 end;
 143
 144
 145 // returns `true` if there is an intersection, and enter coords
 146 // enter coords will be equal to (x0, y0) if starting point is inside the box
 147 // if result is `false`, `inx` and `iny` are undefined
 148 function lineAABBIntersects (x0, y0, x1, y1: Integer; bx, by, bw, bh: Integer; out inx, iny: Integer): Boolean;
 149 var
 150   sx0, sy0, sx1, sy1: Single;
 151 begin
 152   inx := x0;
 153   iny := y0;
 154   result := false;
 155   if (bw < 1) or (bh < 1) then exit;
 156   if (x0 >= bx) and (y0 >= by) and (x0 < bx+bw) and (y0 < by+bh) then begin result := true; exit; end;
 157   sx0 := x0; sy0 := y0;
 158   sx1 := x1; sy1 := y1;
 159   result := clipLine(sx0, sy0, sx1, sy1, bx, by, bx+bw-1, by+bh-1);
 160   if result then
 161   begin
 162     inx := trunc(sx0);
 163     iny := trunc(sy0);
 164     // hack!
 165     if (inx = bx) then Dec(inx) else if (inx = bx+bw-1) then Inc(inx);
 166     if (iny = by) then Dec(iny) else if (iny = by+bh-1) then Inc(iny);
 167   end
 168   else
 169   begin
 170     inx := x1;
 171     iny := y1;
 172   end;
 173 end;
 174
 175
 176 // ////////////////////////////////////////////////////////////////////////// //
 177 {
 178 function sweepAABB (mex0, mey0, mew, meh: Integer; medx, medy: Integer; itx0, ity0, itw, ith: Integer;
 179                     u0: PSingle=nil; hitedge: PSweepEdge=nil; u1: PSingle=nil;
 180                     hitx: PInteger=nil; hity: PInteger=nil): Boolean;
 181 var
 182   tin, tout: Single;
 183
 184   function axisOverlap (me0, me1, it0, it1, d: Integer; he0, he1: TSweepEdge): Boolean; inline;
 185   var
 186     t: Single;
 187   begin
 188     result := false;
 189
 190     if (me1 < it0) then
 191     begin
 192       if (d >= 0) then exit; // oops, no hit
 193       t := (me1-it0+1)/d;
 194       if (t > tin) then begin tin := t; hitedge^ := he1; end;
 195     end
 196     else if (it1 < me0) then
 197     begin
 198       if (d <= 0) then exit; // oops, no hit
 199       t := (me0-it1-1)/d;
 200       if (t > tin) then begin tin := t; hitedge^ := he0; end;
 201     end;
 202
 203     if (d < 0) and (it1 > me0) then
 204     begin
 205       t := (me0-it1-1)/d;
 206       if (t < tout) then tout := t;
 207     end
 208     else if (d > 0) and (me1 > it0) then
 209     begin
 210       t := (me1-it0+1)/d;
 211       if (t < tout) then tout := t;
 212     end;
 213
 214     result := true;
 215   end;
 216
 217 var
 218   mex1, mey1, itx1, ity1, vx, vy, ex, ey: Integer;
 219   htt: TSweepEdge = TSweepEdge.None; // has no sense, who cares
 220 begin
 221   result := false;
 222   if (u0 <> nil) then u0^ := -1.0;
 223   if (u1 <> nil) then u1^ := -1.0;
 224   if (hitx <> nil) then hitx^ := mex0;
 225   if (hity <> nil) then hity^ := mey0;
 226   if (hitedge = nil) then hitedge := @htt else hitedge^ := TSweepEdge.None;
 227
 228   if (mew < 1) or (meh < 1) or (itw < 1) or (ith < 1) then exit;
 229
 230   mex1 := mex0+mew-1;
 231   mey1 := mey0+meh-1;
 232   itx1 := itx0+itw-1;
 233   ity1 := ity0+ith-1;
 234
 235   // check if they are overlapping right now (SAT)
 236   //if (mex1 >= itx0) and (mex0 <= itx1) and (mey1 >= ity0) and (mey0 <= ity1) then begin result := true; exit; end;
 237
 238   if (medx = 0) and (medy = 0) then exit; // both boxes are sationary
 239
 240   // treat b as stationary, so invert v to get relative velocity
 241   vx := -medx;
 242   vy := -medy;
 243
 244   tin := -100000000.0;
 245   tout := 100000000.0;
 246
 247   if not axisOverlap(mex0, mex1, itx0, itx1, vx, TSweepEdge.Right, TSweepEdge.Left) then exit;
 248   if not axisOverlap(mey0, mey1, ity0, ity1, vy, TSweepEdge.Bottom, TSweepEdge.Top) then exit;
 249
 250   if (u0 <> nil) then u0^ := tin;
 251   if (u1 <> nil) then u1^ := tout;
 252
 253   if (tin <= tout) and (tin >= 0.0) and (tin <= 1.0) then
 254   begin
 255     result := true;
 256     if (hitx <> nil) or (hity <> nil) then
 257     begin
 258       ex := mex0+round(medx*tin);
 259       ey := mey0+round(medy*tin);
 260       // just in case, compensate for floating point inexactness
 261       if (ex >= itx0) and (ey >= ity0) and (ex < itx0+itw) and (ey < ity0+ith) then
 262       begin
 263         ex := mex0+trunc(medx*tin);
 264         ey := mey0+trunc(medy*tin);
 265       end;
 266       if (hitx <> nil) then hitx^ := ex;
 267       if (hity <> nil) then hity^ := ey;
 268     end;
 269   end;
 270 end;
 271 }
 272
 273 function sweepAABB (mex0, mey0, mew, meh: Integer; medx, medy: Integer; itx0, ity0, itw, ith: Integer;
 274                     out u0: Single): Boolean;
 275 var
 276   tin, tout: Single;
 277
 278   function axisOverlap (me0, me1, it0, it1, d: Integer): Boolean; inline;
 279     var t: Single;
 280   begin
 281     Result := false;
 282
 283     if me1 < it0 then
 284     begin
 285       if (d >= 0) then
 286         exit; // oops, no hit
 287       t := (me1 - it0 + 1) / d;
 288       if t > tin then
 289         tin := t;
 290     end
 291     else if it1 < me0 then
 292     begin
 293       if d <= 0 then
 294         exit; // oops, no hit
 295       t := (me0 - it1 - 1) / d;
 296       if t > tin then
 297         tin := t;
 298     end;
 299
 300     if (d < 0) and (it1 > me0) then
 301     begin
 302       t := (me0 - it1 - 1) / d;
 303       if t < tout then
 304         tout := t;
 305     end
 306     else if (d > 0) and (me1 > it0) then
 307     begin
 308       t := (me1 - it0 + 1) / d;
 309       if t < tout then
 310         tout := t;
 311     end;
 312
 313     result := true;
 314   end;
 315
 316 begin
 317   Result := False;
 318   u0 := -1;
 319
 320   if (mew >= 1) and (meh >= 1) and (itw >= 1) and (ith >= 1) and (medx <> 0) and (medy <> 0) then
 321   begin
 322     tin := -100000000.0;
 323     tout := 100000000.0;
 324     if axisOverlap(mex0, mex0 + mew - 1, itx0, itx0 + itw - 1, -medx) then
 325     begin
 326       if not axisOverlap(mey0, mey0 + meh - 1, ity0, ity0 + ith - 1, -medy) then
 327       begin
 328         u0 := tin;
 329         Result := (tin <= tout) and (tin >= 0.0) and (tin <= 1.0);
 330       end;
 331     end;
 332   end;
 333 end;
 334
 335
 336 end.