/// <summary>
/// Recursively casts light into cells. Operates on a single octant.
/// </summary>
/// <param name="bitMap">The cell grid definition.</param>
/// <param name="gridPosn">The player's position within the grid.</param>
/// <param name="viewRadius">The view radius; can be a fractional value.</param>
/// <param name="startColumn">Current column; pass 1 as initial value.</param>
/// <param name="leftViewSlope">Slope of the left (upper) view edge; pass 1.0 as
/// the initial value.</param>
/// <param name="rightViewSlope">Slope of the right (lower) view edge; pass 0.0 as
/// the initial value.</param>
/// <param name="txfrm">Coordinate multipliers for the octant transform.</param>
///
/// Maximum recursion depth is (Ceiling(viewRadius)).
private static void CastLight(ObjMap objMap, Vector2 gridPosn, float viewRadius,
int startColumn, float leftViewSlope, float rightViewSlope, OctantTransform txfrm)
{
//Debug.Assert(leftViewSlope >= rightViewSlope);
// Used for distance test.
float viewRadiusSq = viewRadius * viewRadius;
int viewCeiling = (int)Mathf.Ceil(viewRadius);
// Set true if the previous cell we encountered was blocked.
bool prevWasBlocked = false;
// As an optimization, when scanning past a block we keep track of the
// rightmost corner (bottom-right) of the last one seen. If the next cell
// is empty, we can use this instead of having to compute the top-right corner
// of the empty cell.
float savedRightSlope = -1;
int xDim = objMap.getObjMap().GetLength(0);
int yDim = objMap.getObjMap().GetLength(1);
// Outer loop: walk across each column, stopping when we reach the visibility limit.
for (int currentCol = startColumn; currentCol <= viewCeiling; currentCol++)
{
int xc = currentCol;
// Inner loop: walk down the current column. We start at the top, where X==Y.
//
// TODO: we waste time walking across the entire column when the view area
// is narrow. Experiment with computing the possible range of cells from
// the slopes, and iterate over that instead.
for (int yc = currentCol; yc >= 0; yc--)
{
// Translate local coordinates to grid coordinates. For the various octants
// we need to invert one or both values, or swap X for Y.
int gridX = (int)gridPosn.x + xc * txfrm.xx + yc * txfrm.xy;
int gridY = (int)gridPosn.y + xc * txfrm.yx + yc * txfrm.yy;
// Range-check the values. This lets us avoid the slope division for blocks
// that are outside the grid.
//
// Note that, while we will stop at a solid column of blocks, we do always
// start at the top of the column, which may be outside the grid if we're (say)
// checking the first octant while positioned at the north edge of the map.
if (gridX < 0 || gridX >= xDim || gridY < 0 || gridY >= yDim)
{
continue;
}
// Compute slopes to corners of current block. We use the top-left and
// bottom-right corners. If we were iterating through a quadrant, rather than
// an octant, we'd need to flip the corners we used when we hit the midpoint.
//
// Note these values will be outside the view angles for the blocks at the
// ends -- left value > 1, right value < 0.
float leftBlockSlope = (yc + 0.5f) / (xc - 0.5f);
float rightBlockSlope = (yc - 0.5f) / (xc + 0.5f);
// Check to see if the block is outside our view area. Note that we allow
// a "corner hit" to make the block visible. Changing the tests to >= / <=
// will reduce the number of cells visible through a corner (from a 3-wide
// swath to a single diagonal line), and affect how far you can see past a block
// as you approach it. This is mostly a matter of personal preference.
if (rightBlockSlope > leftViewSlope)
{
// Block is above the left edge of our view area; skip.
continue;
}
else if (leftBlockSlope < rightViewSlope)
{
// Block is below the right edge of our view area; we're done.
break;
}
// This cell is visible, given infinite vision range. If it's also within
// our finite vision range, light it up.
//
// To avoid having a single lit cell poking out N/S/E/W, use a fractional
// viewRadius, e.g. 8.5.
//
// TODO: we're testing the middle of the cell for visibility. If we tested
// the bottom-left corner, we could say definitively that no part of the
// cell is visible, and reduce the view area as if it were a wall. This
// could reduce iteration at the corners.
float distanceSquared = xc * xc + yc * yc;
if (distanceSquared <= viewRadiusSq)
{
//grid.SetLight(gridX, gridY, distanceSquared);
objMap.castLight(gridX, gridY);
lightenedArea.Add(objMap.getObject(gridX, gridY));
}
bool curBlocked = objMap.isBlocking(gridX, gridY); // grid.IsWall(gridX, gridY);
if (prevWasBlocked)
{
if (curBlocked)
{
// Still traversing a column of walls.
savedRightSlope = rightBlockSlope;
}
else
{
// Found the end of the column of walls. Set the left edge of our
// view area to the right corner of the last wall we saw.
prevWasBlocked = false;
leftViewSlope = savedRightSlope;
}
}
else
{
if (curBlocked)
{
// Found a wall. Split the view area, recursively pursuing the
// part to the left. The leftmost corner of the wall we just found
// becomes the right boundary of the view area.
//
// If this is the first block in the column, the slope of the top-left
// corner will be greater than the initial view slope (1.0). Handle
// that here.
if (leftBlockSlope <= leftViewSlope)
{
CastLight(objMap, gridPosn, viewRadius, currentCol + 1,
leftViewSlope, leftBlockSlope, txfrm);
}
// Once that's done, we keep searching to the right (down the column),
// looking for another opening.
prevWasBlocked = true;
savedRightSlope = rightBlockSlope;
}
}
}
// Open areas are handled recursively, with the function continuing to search to
// the right (down the column). If we reach the bottom of the column without
// finding an open cell, then the area defined by our view area is completely
// obstructed, and we can stop working.
if (prevWasBlocked)
{
break;
}
}
}
/// <summary>
/// Recursively casts light into cells. Operates on a single octant.
/// </summary>
/// <param name="grid">The cell grid definition.</param>
/// <param name="gridPosnX">The player's X-position within the grid.</param>
/// <param name="gridPosnY">The player's Y-position within the grid.</param>
/// <param name="viewRadius">The view radius; can be a fractional value.</param>
/// <param name="startColumn">Current column; pass 1 as initial value.</param>
/// <param name="leftViewSlope">Slope of the left (upper) view edge; pass 1.0 as
/// the initial value.</param>
/// <param name="rightViewSlope">Slope of the right (lower) view edge; pass 0.0 as
/// the initial value.</param>
/// <param name="txfrm">Coordinate multipliers for the octant transform.</param>
///
/// Maximum recursion depth is (Ceiling(viewRadius)).
private static void CastLight(ICellGrid grid, int gridPosnX, int gridPosnY, IViewer viewer,
int startColumn, float leftViewSlope, float rightViewSlope, OctantTransform txfrm)
{
//Debug.Assert(leftViewSlope >= rightViewSlope);
// Used for distance test.
float viewRadiusSq = viewer.ViewDistance * viewer.ViewDistance;
int viewCeiling = (int)Math.Ceiling(viewer.ViewDistance);
// Set true if the previous cell we encountered was blocked.
bool prevWasBlocked = false;
// As an optimization, when scanning past a block we keep track of the
// rightmost corner (bottom-right) of the last one seen. If the next cell
// is empty, we can use this instead of having to compute the top-right corner
// of the empty cell.
float savedRightSlope = -1;
int xDim = grid.xDim;
int yDim = grid.yDim;
// Outer loop: walk across each column, stopping when we reach the visibility limit.
for (int currentCol = startColumn; currentCol <= viewCeiling; currentCol++)
{
int xc = currentCol;
// Inner loop: walk down the current column. We start at the top, where X==Y.
//
// TODO: we waste time walking across the entire column when the view area
// is narrow. Experiment with computing the possible range of cells from
// the slopes, and iterate over that instead.
for (int yc = currentCol; yc >= 0; yc--)
{
// Translate local coordinates to grid coordinates. For the various octants
// we need to invert one or both values, or swap X for Y.
int gridX = gridPosnX + xc * txfrm.xx + yc * txfrm.xy;
int gridY = gridPosnY + xc * txfrm.yx + yc * txfrm.yy;
// Range-check the values. This lets us avoid the slope division for blocks
// that are outside the grid.
//
// Note that, while we will stop at a solid column of blocks, we do always
// start at the top of the column, which may be outside the grid if we're (say)
// checking the first octant while positioned at the north edge of the map.
if (gridX < 0 || gridX >= xDim || gridY < 0 || gridY >= yDim)
{
continue;
}
// Compute slopes to corners of current block. We use the top-left and
// bottom-right corners. If we were iterating through a quadrant, rather than
// an octant, we'd need to flip the corners we used when we hit the midpoint.
//
// Note these values will be outside the view angles for the blocks at the
// ends -- left value > 1, right value < 0.
float leftBlockSlope = (yc + 0.5f) / (xc - 0.5f);
float rightBlockSlope = (yc - 0.5f) / (xc + 0.5f);
// Check to see if the block is outside our view area. Note that we allow
// a "corner hit" to make the block visible. Changing the tests to >= / <=
// will reduce the number of cells visible through a corner (from a 3-wide
// swath to a single diagonal line), and affect how far you can see past a block
// as you approach it. This is mostly a matter of personal preference.
if (rightBlockSlope >= leftViewSlope)
{
// Block is above the left edge of our view area; skip.
continue;
}
else if (leftBlockSlope <= rightViewSlope)
{
// Block is below the right edge of our view area; we're done.
break;
}
// This cell is visible, given infinite vision range. If it's also within
// our finite vision range, light it up.
//
// To avoid having a single lit cell poking out N/S/E/W, use a fractional
// viewRadius, e.g. 8.5.
//
// TODO: we're testing the middle of the cell for visibility. If we tested
// the bottom-left corner, we could say definitively that no part of the
// cell is visible, and reduce the view area as if it were a wall. This
// could reduce iteration at the corners.
float distanceSquared = xc * xc + yc * yc;
if (distanceSquared <= viewRadiusSq)
{
grid.SetLight(gridX, gridY, distanceSquared, viewer);
}
bool curBlocked = grid.IsWall(gridX, gridY);
if (prevWasBlocked)
{
if (curBlocked)
{
// Still traversing a column of walls.
savedRightSlope = rightBlockSlope;
}
else
{
// Found the end of the column of walls. Set the left edge of our
// view area to the right corner of the last wall we saw.
prevWasBlocked = false;
leftViewSlope = savedRightSlope;
}
}
else
{
if (curBlocked)
{
// Found a wall. Split the view area, recursively pursuing the
// part to the left. The leftmost corner of the wall we just found
// becomes the right boundary of the view area.
//
// If this is the first block in the column, the slope of the top-left
// corner will be greater than the initial view slope (1.0). Handle
// that here.
if (leftBlockSlope <= leftViewSlope)
{
CastLight(grid, gridPosnX, gridPosnY, viewer, currentCol + 1,
leftViewSlope, leftBlockSlope, txfrm);
}
// Once that's done, we keep searching to the right (down the column),
// looking for another opening.
prevWasBlocked = true;
savedRightSlope = rightBlockSlope;
}
}
}
// Open areas are handled recursively, with the function continuing to search to
// the right (down the column). If we reach the bottom of the column without
// finding an open cell, then the area defined by our view area is completely
// obstructed, and we can stop working.
if (prevWasBlocked)
{
break;
}
}
}