Talk:Spiral Path FOV
From RogueBasin
Here is an example of a spiral-path-like algorithm, modelled after the one found at http://www.geocities.com/temerra/los_rays.html, written in C-like C++.
It is used in the game "deliantra", and posted here because I couldn't find nice and simple spirla path examples.
If somebody knows a better place than the disucssion page, feel free to move it, or delete it. I hereby place this code into the public domain.
The code places a value from 0..3 (fully visible .. hardly visible) or 100 (not seen) into the pl->los array. It uses a special diagonal edge fixup. The sign function returns -1 or +1, depending on the sign, and sign0 additionally 0 for 0. It is good for coordinates <<128 only, but both los_info and point structures can usually be indexed very efficiently due to their small size.
- The example at the geocities website looks really nice. Do you perhaps know who the author is? We could use the images to explain the algorithms better. --Soyweiser 13:59, 26 December 2008 (CET)
#define MAP_CLIENT_X 32
#define MAP_CLIENT_Y 32
#define LOS_BLOCKED 100
enum {
LOS_XI = 0x01,
LOS_YI = 0x02,
};
struct los_info
{
sint8 xo, yo; // obscure angle
sint8 xe, ye; // angle deviation
uint8 culled; // culled from "tree"
uint8 queued; // already queued
uint8 visible;
uint8 flags; // LOS_XI/YI
};
// temporary storage for the los algorithm,
// one los_info for each lightable map space
static los_info los[MAP_CLIENT_X][MAP_CLIENT_Y];
struct point
{
sint8 x, y;
};
// minimum size, but must be a power of two
#define QUEUE_LENGTH ((MAP_CLIENT_X + MAP_CLIENT_Y) * 2)
// a queue of spaces to calculate
static point queue [QUEUE_LENGTH];
static int q1, q2; // queue start, end
// enqueue a single mapspace, but only if it hasn't
// been enqueued yet.
static void
enqueue (sint8 dx, sint8 dy, uint8 flags = 0)
{
sint8 x = LOS_X0 + dx;
sint8 y = LOS_Y0 + dy;
if (x < 0 || x >= MAP_CLIENT_X) return;
if (y < 0 || y >= MAP_CLIENT_Y) return;
los_info &l = los[x][y];
l.flags |= flags;
if (l.queued)
return;
l.queued = 1;
queue[q1].x = dx;
queue[q1].y = dy;
q1 = (q1 + 1) & (QUEUE_LENGTH - 1);
}
// run the los algorithm
// this is a variant of a spiral los algorithm taken from
// http://www.geocities.com/temerra/los_rays.html
// which has been simplified and changed considerably, but
// still is basically the same algorithm.
static void
do_los (player *pl)
{
memset (los, 0, sizeof (los));
q1 = 0; q2 = 0;
enqueue (0, 0); // enqueue center
// treat the origin specially
los[LOS_X0][LOS_Y0].visible = 1;
pl->los[LOS_X0][LOS_Y0] = 0;
// loop over all enqueued points until the queue is empty
// the order in which this is done ensures that we
// never touch a mapspace whose input spaces we haven't checked
// yet.
while (q1 != q2)
{
sint8 dx = queue[q2].x;
sint8 dy = queue[q2].y;
q2 = (q2 + 1) & (QUEUE_LENGTH - 1);
sint8 x = LOS_X0 + dx;
sint8 y = LOS_Y0 + dy;
los_info &l = los[x][y];
if (expect_true (l.flags & (LOS_XI | LOS_YI)))
{
l.culled = 1;
// check contributing spaces, first horizontal
if (expect_true (l.flags & LOS_XI))
{
los_info *xi = &los[x - sign (dx)][y];
// don't cull unless obscured
l.culled &= !xi->visible;
/* merge input space */
if (expect_false (xi->xo || xi->yo))
{
// The X input can provide two main pieces of information:
// 1. Progressive X obscurity.
// 2. Recessive Y obscurity.
// Progressive X obscurity, favouring recessive input angle
if (xi->xe > 0 && l.xo == 0)
{
l.xe = xi->xe - xi->yo;
l.ye = xi->ye + xi->yo;
l.xo = xi->xo;
l.yo = xi->yo;
}
// Recessive Y obscurity
if (xi->ye <= 0 && xi->yo > 0 && xi->xe > 0)
{
l.ye = xi->yo + xi->ye;
l.xe = xi->xe - xi->yo;
l.xo = xi->xo;
l.yo = xi->yo;
}
}
}
// check contributing spaces, last vertical, identical structure
if (expect_true (l.flags & LOS_YI))
{
los_info *yi = &los[x][y - sign (dy)];
// don't cull unless obscured
l.culled &= !yi->visible;
/* merge input space */
if (expect_false (yi->yo || yi->xo))
{
// The Y input can provide two main pieces of information:
// 1. Progressive Y obscurity.
// 2. Recessive X obscurity.
// Progressive Y obscurity, favouring recessive input angle
if (yi->ye > 0 && l.yo == 0)
{
l.ye = yi->ye - yi->xo;
l.xe = yi->xe + yi->xo;
l.yo = yi->yo;
l.xo = yi->xo;
}
// Recessive X obscurity
if (yi->xe <= 0 && yi->xo > 0 && yi->ye > 0)
{
l.xe = yi->xo + yi->xe;
l.ye = yi->ye - yi->xo;
l.yo = yi->yo;
l.xo = yi->xo;
}
}
}
// check whether this space blocks the view
if (world_blocksview_at (x, y))
{
l.xo = l.xe = abs (dx);
l.yo = l.ye = abs (dy);
// we obscure dependents, but might be visible
// copy the los from the square towards the player,
// so outward diagonal corners are lit.
pl->los[x][y] = los[x - sign0 (dx)][y - sign0 (dy)].visible ? 0 : LOS_BLOCKED;
l.visible = false;
}
else
{
// we are not blocked, so calculate visibility, by checking
// whether we are inside or outside the shadow
l.visible = (l.xe <= 0 || l.xe > l.xo)
&& (l.ye <= 0 || l.ye > l.yo);
pl->los[x][y] = l.culled ? LOS_BLOCKED
: l.visible ? 0
: 3;
}
}
// Expands by the unit length in each component's current direction.
// If a component has no direction, then it is expanded in both of its
// positive and negative directions.
if (!l.culled)
{
if (dx >= 0) enqueue (dx + 1, dy, LOS_XI);
if (dx <= 0) enqueue (dx - 1, dy, LOS_XI);
if (dy >= 0) enqueue (dx, dy + 1, LOS_YI);
if (dy <= 0) enqueue (dx, dy - 1, LOS_YI);
}
}
}
--schmorp 04:53, 20 December 2008 (CET)
