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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/api.texi | 107 |
1 files changed, 107 insertions, 0 deletions
diff --git a/doc/api.texi b/doc/api.texi index 47e16f5..a2e546d 100644 --- a/doc/api.texi +++ b/doc/api.texi @@ -363,6 +363,7 @@ detection. * Basics:: Commonly used, miscellaneous things. * Vectors:: Euclidean vectors. * Rectangles:: Axis-aligned bounding boxes. +* Grid:: Spatial partitioning for bounding boxes. * Matrices:: Transformation matrices. * Quaternions:: Rotations about an arbitrary axis. * Easings:: Easing functions for interesting animations. @@ -781,6 +782,112 @@ Restrict the coordinates of the 2D vector @var{v} so that they are within the bounds of @var{rect}. @var{v} is modified in-place. @end deffn +@node Grid +@subsection Grid + +The @code{(chickadee math grid)} module provides a simple spatial +partitioning system for axis-aligned bounding boxes +(@pxref{Rectangles}) in 2D space. The grid divides the world into +tiles and keeps track of which rectangles occupy which tiles. When +there are lots of moving objects in the game world that need collision +detection, the grid greatly speeds up the process. Instead of +checking collisions of each object against every other object (an +O(n^2) operation), the grid quickly narrows down which objects could +possibly be colliding and only performs collision testing against a +small set of objects. + +In addition to checking for collisions, the grid also handles the +resolution of collisions. Exactly how each collision is resolved is +user-defined. A player bumping into a wall may slide against it. An +enemy colliding with a projectile shot by the player may get pushed +back in the opposite direction. Two players colliding may not need +resolution at all and will just pass through each other. The way this +works is that each time an object (A) is moved within the grid, the +grid looks for an object (B) that may possibly be colliding with A. A +user-defined procedure known as a ``filter'' is then called with both +A and B. If the filter returns @code{#f}, it means that even if A and +B are colliding, no collision resolution is needed. In this case the +grid won't waste time checking if they really do collide because it +doesn't matter. If A and B are collidable, then the filter returns a +procedure that implements the resolution technique. The grid will +then perform a collision test. If A and B are colliding, the resolver +procedure is called. It's the resolvers job to adjust the objects +such that they are no longer colliding. The grid module comes with a +very simple resolution procedure, @code{slide}, that adjusts object A +by the smallest amount so that it no longer overlaps with B. By using +this filtering technique, a game can resolve collisions between +different objects in different ways. + +@deffn {Procedure} make-grid [@var{cell-size} 64] +Return a new grid partitioned into @var{cell-size} tiles. +@end deffn + +@deffn {Procedure} grid? @var{obj} +Return @code{#t} if @var{obj} is a grid. +@end deffn + +@deffn {Procedure} cell? @var{obj} +Return @code{#t} if @var{obj} is a grid cell. +@end deffn + +@deffn {Procedure} cell-count @var{cell} +Return the number of items in @var{cell}. +@end deffn + +@deffn {Procedure} grid-cell-size @var{grid} +Return the cell size of @var{grid}. +@end deffn + +@deffn {Procedure} grid-cell-count @var{grid} +Return the number of cells currently in @var{grid}. +@end deffn + +@deffn {Procedure} grid-item-count @var{grid} +Return the number of items in @var{grid}. +@end deffn + +@deffn {Procedure} grid-add @var{grid} @var{item} @var{x} @var{y} @ + @var{width} @var{height} + +Add @var{item} to @var{grid} represented by the axis-aligned bounding +box whose lower-left corner is at (@var{x}, @var{y}) and is +@var{width} x @var{height} in size. +@end deffn + +@deffn {Procedure} grid-remove @var{grid} @var{item} +Return @var{item} from @var{grid}. +@end deffn + +@deffn {Procedure} grid-clear @var{grid} +Remove all items from @var{grid}. +@end deffn + +@deffn {Procedure} grid-move @var{grid} @var{item} @var{position} @var{filter} +Attempt to move @var{item} in @var{grid} to @var{position} (a 2D +vector) and check for collisions. For each collision, @var{filter} +will be called with two arguments: @var{item} and the item it collided +with. If a collision occurs, @var{position} may be modified to +resolve the colliding objects. +@end deffn + +@deffn {Procedure} for-each-cell @var{proc} @var{grid} [@var{rect}] +Call @var{proc} with each cell in @var{grid} that intersects +@var{rect}, or every cell if @var{rect} is @code{#f}. +@end deffn + +@deffn {Procedure} for-each-item @var{proc} @var{grid} +Call @var{proc} for each item in @var{grid}. +@end deffn + +@deffn {Procedure} slide @var{item} @var{item-rect} @ + @var{other} @var{other-rect} @var{goal} + +Resolve the collision that occurs between @var{item} and @var{other} +when moving @var{item-rect} to @var{goal} by sliding @var{item-rect} +the minimum amount needed to make it no longer overlap +@var{other-rect}. +@end deffn + @node Matrices @subsection Matrices |