shithub: duke3d

--- a/Engine/src/engine.c

+++ b/Engine/src/engine.c

@@ -4468,7 +4468,7 @@

  Algorithm: This is an optimized raycasting inside polygon test:

  http://en.wikipedia.org/wiki/Point_in_polygon#Ray_casting_algorithm

- The goal is to follow an horizontal ray passing by (x,y) and count how many

+ The goal is to follow an ***horizontal*** ray passing by (x,y) and count how many

  wall are being crossed.

  If it is an odd number of time: (x,y) is inside the sector.

  If it is an even nymber of time:(x,y) is outside the sector.

@@ -4493,6 +4493,7 @@

         // Compare the sign of y1 and y2.

         // If (y1^y2) < 0 : y1 and y2 have different sign bit:  y is between wal->y and wall[wal->point2].y.

+        // The goal is to not take into consideration any wall that is totally above or totally under the point [x,y].

         if ((y1^y2) < 0)

             x1 = wal->x-x;

@@ -4501,13 +4502,13 @@

             //If (x1^x2) >= 0 x1 and x2 have identic sign bit: x is on the left or the right of both wal->x and wall[wal->point2].x.

             if ((x1^x2) >= 0)

-                // If (x,y) is on totally on the left or on the right, just count x1 (which indicate if we are on

-                // (x,y) is on the left or on the right.

+                // If (x,y) is totally on the left or on the right, just count x1 (which indicate if we are on

+                // on the left or on the right.

                 wallCrossed ^= x1;

             else

-                // This is the most complicated case: X is between x1 and x2 and y is between y1 and y2.

+                // This is the most complicated case: X is between x1 and x2, we need a fine grained test.

                 // We need to know exactly if it is on the left or on the right in order to know if the ray

                 // is crossing the wall or not,

                 // The sign of the Cross-Product can answer this case :) !