borgware-2d/games/tetris/playfield.c

#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <inttypes.h>
#include "../../autoconf.h"
#include "playfield.h"
#include "piece.h"


/***************************
 * non-interface functions *
 ***************************/

/* Function:         tetris_playfield_hoverStatus;
 * Description:      determines if piece is either hovering or gliding
 * Argument pPl:     the playfield we want information from
 * Return value:     TETRIS_PFS_HOVERING or TETRIS_PFS_GLIDING
 */
tetris_playfield_status_t tetris_playfield_hoverStatus(tetris_playfield_t* pPl)
{
	// if the piece touches the dump we ensure that the status is "gliding"
	if (tetris_playfield_collision(pPl, pPl->nColumn, pPl->nRow + 1))
	{
		return TETRIS_PFS_GLIDING;
	}
	// otherwise the status must be "hovering"
	else
	{
		return TETRIS_PFS_HOVERING;
	}
}


/****************************
 * construction/destruction *
 ****************************/

/* Function:         tetris_playfield_construct
 * Description:      constructs a playfield with the given dimensions
 * Argument nWidth:  width of playfield (4 <= n <= 16)
 * Argument nHeight: height of playfield (4 <= n <= 124)
 * Return value:     pointer to a newly created playfield
 */
tetris_playfield_t *tetris_playfield_construct(int8_t nWidth,
                                               int8_t nHeight)
{
	assert((nWidth >= 4) && (nWidth <= 16));
	assert((nHeight >= 4) && (nHeight <= 124));

	tetris_playfield_t *pPlayfield =
		(tetris_playfield_t*) malloc(sizeof(tetris_playfield_t));

	if (pPlayfield != NULL)
	{
		// allocating mem for dump array
		pPlayfield->dump = (uint16_t*) calloc(nHeight, sizeof(uint16_t));

		if (pPlayfield->dump != NULL)
		{
			// setting desired attributes
			pPlayfield->nFirstMatterRow = nHeight - 1;
			pPlayfield->nWidth = nWidth;
			pPlayfield->nHeight = nHeight;
			tetris_playfield_reset(pPlayfield);

			return pPlayfield;
		}
		else
		{
			free(pPlayfield);
			pPlayfield = NULL;
		}
	}
	return NULL;
}


/* Function:     tetris_playfield_destruct
 * Description:  destructs a playfield
 * Argument pPl: pointer to the playfield to be destructed
 * Return value: void
 */
void tetris_playfield_destruct(tetris_playfield_t *pPl)
{
	assert(pPl != NULL);

	// if memory for the dump array has been allocated, free it
	if (pPl->dump != NULL)
	{
		free(pPl->dump);
	}
	free(pPl);
}


/*******************************
 * playfield related functions *
 *******************************/

/* Function:     tetris_playfield_reset
 * Description:  resets playfield to begin a new game
 * Argument pPl: playfield to perform action on
 * Return value: void
 */
void tetris_playfield_reset(tetris_playfield_t *pPl)
{
	assert(pPl != NULL);

	pPl->pPiece = NULL;
	pPl->nColumn = 0;
	pPl->nRow = 0;
	pPl->nRowMask = 0;

	// clear dump if it has been allocated in memory
	if (pPl->dump != NULL)
	{
		memset(pPl->dump, 0, pPl->nHeight);
	}

	pPl->status = TETRIS_PFS_READY;
}


int8_t tetris_playfield_getPieceStartPos(tetris_piece_t *pPiece)
{
	// set vertical start position (first piece row with matter at pos. 1)
	uint16_t nPieceMap = tetris_piece_getBitmap(pPiece);
	uint16_t nElementMask = 0xF000;
	int8_t nRow = -3;
	while ((nPieceMap & nElementMask) == 0)
	{
		++nRow;
		nElementMask >>= 4;
	}
	if (nRow < 0)
	{
		++nRow;
	}

	return nRow;
}


/* Function:            tetris_playfield_insertPiece
 * Description:         inserts a new piece
 * Argument pPl:        playfield to perform action on
 * Argument pPiece:     piece to be inserted
 * Argument ppOldPiece: [out] indirect pointer to former piece for deallocation
 * Return value:        void
 */
void tetris_playfield_insertPiece(tetris_playfield_t *pPl,
                                  tetris_piece_t *pPiece,
                                  tetris_piece_t** ppOldPiece)
{
	assert((pPl != NULL) && (pPiece != NULL) && (ppOldPiece != NULL));

	// a piece can only be inserted in state TETRIS_PFS_READY
	assert(pPl->status == TETRIS_PFS_READY);

	// row mask is now meaningless
	pPl->nRowMask = 0;

	// replace old piece
	*ppOldPiece = pPl->pPiece;
	pPl->pPiece = pPiece;

	// set horizontal start position (in the middle of the top line)
	pPl->nColumn = (pPl->nWidth - 2) / 2;

	// set vertical start position (first piece row with matter at pos. 1)
	pPl->nRow = tetris_playfield_getPieceStartPos(pPl->pPiece);

	// did we already collide with something?
	if (tetris_playfield_collision(pPl, pPl->nColumn, pPl->nRow) == 1)
	{
		// game over man, game over!!
		pPl->status = TETRIS_PFS_GAMEOVER;
	}
	else
	{
		// bring it on!
		pPl->status = tetris_playfield_hoverStatus(pPl);
	}
}


/* Function:         tetris_playfield_collision
 * Description:      detects if piece collides with s.th. at a given position
 * Argument pPl:     playfield to perform action on
 * Argument nColumn: column where the piece should be moved
 * Argument nRow:    row where the piece should be moved
 * Return value:     1 for collision, 0 otherwise
 */
uint8_t tetris_playfield_collision(tetris_playfield_t *pPl,
                                   int8_t nColumn,
                                   int8_t nRow)
{
	assert(pPl != NULL);

	// only allow coordinates which are within sane ranges
	assert((nColumn > -4) && (nColumn < pPl->nWidth));
	assert((nRow > -4) && (nRow < pPl->nHeight));

	// The rows of a piece get compared with the background one by one
	// until either a collision occures or all rows are compared. Both the
	// piece row and the part of the playfield it covers are represented in
	// 4 bits which were singled out from their corresponding uint16_t
	// values and are aligned to LSB. In case where a piece overlaps with
	// either the left or the right border we "enhance" the playfield part
	// via bit shifting and set all bits representing the border to 1.
	//
	// NOTE: LSB represents the left most position.
	uint16_t nPieceMap = tetris_piece_getBitmap(pPl->pPiece);
	uint16_t nPlayfieldPart;
	uint16_t nPieceRowMap;

	// negative nRow values indicate that the piece hasn't fully entered the
	// playfield yet which requires special treatment if the piece overlaps
	// with either the left or the right border
	if (nRow < 0)
	{
		uint16_t nBorderMask = 0x0000;
		// piece overlaps with left border
		if (nColumn < 0)
		{
			nBorderMask = 0x1111 << (-nColumn - 1);
		}
		// piece overlaps with right border
		else if ((nColumn + 3) >= pPl->nWidth)
		{
			nBorderMask = 0x8888 >> ((nColumn + 3) - pPl->nWidth);
		}
		// return if piece collides with border
		if ((nPieceMap & nBorderMask) != 0)
		{
			return 1;
		}
	}

	// here we check the part which has already entered the playfield
	for (int8_t y = (nRow < 0) ? -nRow : 0; y < 4; ++y)
	{
		// current piece row overlaps with lower border
		if ((y + nRow) >= pPl->nHeight)
		{
			// all 4 bits represent the lower border
			nPlayfieldPart = 0x000F;
		}
		// piece overlaps with left border
		else if (nColumn < 0)
		{
			// clear all bits we are not interested in
			nPlayfieldPart = (pPl->dump[y + nRow] & (0x000F >> -nColumn));
			// add zeros to the left (the bits "behind" the left border)
			nPlayfieldPart <<= -nColumn;
			// set bits beyond left border to 1
			nPlayfieldPart |= 0x000F >> (4 + nColumn);
		}
		// piece overlaps with right border
		else if ((nColumn + 3) >= pPl->nWidth)
		{
			// align the bits we are interested in to LSB
			// (thereby clearing the rest)
			nPlayfieldPart = pPl->dump[y + nRow] >> nColumn;
			// set bits beyond right border to 1
			nPlayfieldPart |= 0xFFF8 >> (nColumn + 3 - pPl->nWidth);
		}
		// current row neither overlaps with left, right nor lower border
		else
		{
			// clear all bits we are not interested in and align the
			// remaing row to LSB
			nPlayfieldPart =
				(pPl->dump[y + nRow] & (0x000F << nColumn)) >> nColumn;
		}

		// clear all bits of the piece we are not interested in and
		// align the remaing row to LSB
		nPieceRowMap = (nPieceMap & (0x000F << (y << 2))) >> (y << 2);

		// finally check for a collision
		if ((nPlayfieldPart & nPieceRowMap) != 0)
		{
			return 1;
		}
	}

	// if we reach here, no collision was detected
	return 0;
}


/* Function:     tetris_playfield_advancePiece
 * Description:  lowers piece by one row or finally docks it
 * Argument pPl: playfield to perform action on
 * Return value: void
 */
void tetris_playfield_advancePiece(tetris_playfield_t *pPl)
{
	assert(pPl != NULL);

	// a piece can only be lowered if it is hovering or gliding
	assert ((pPl->status == TETRIS_PFS_HOVERING) ||
		(pPl->status == TETRIS_PFS_GLIDING));

	if (tetris_playfield_collision(pPl, pPl->nColumn, pPl->nRow + 1))
	{
		uint16_t nPiece = tetris_piece_getBitmap(pPl->pPiece);

		// Is the playfield filled up?
		if ((pPl->nRow < 0) && (nPiece & (0x0FFF >> ((3 + pPl->nRow) << 2))) != 0)
		{
			pPl->status = TETRIS_PFS_GAMEOVER;
		}
		else
		{
			// determine valid start point for dump index
			int8_t nStartRow = ((pPl->nRow + 3) < pPl->nHeight) ?
				(pPl->nRow + 3) : pPl->nHeight - 1;
			for (int8_t i = nStartRow; i >= pPl->nRow; --i)
			{
				int8_t y = i - pPl->nRow;

				// clear all bits of the piece we are not interested in and
				// align the rest to LSB
				uint16_t nPieceMap = (nPiece & (0x000F << (y << 2))) >> (y << 2);
				// shift the remaining content to the current column
				if (pPl->nColumn >= 0)
				{
					nPieceMap <<= pPl->nColumn;
				}
				else
				{
					nPieceMap >>= -pPl->nColumn;
				}
				// embed piece in playfield
				pPl->dump[i] |= nPieceMap;
			}

			// update value for the highest row with matter
			int8_t nPieceRow = pPl->nRow;
			uint16_t nMask = 0x000F;
			for (int i = 0; i < 4; ++i, nMask <<= 4)
			{
				if ((nMask & nPiece) != 0)
				{
					nPieceRow += i;
					break;
				}
			}
			pPl->nFirstMatterRow = (pPl->nFirstMatterRow > nPieceRow) ?
					nPieceRow : pPl->nFirstMatterRow;

			// the piece has finally been docked
			pPl->status = TETRIS_PFS_DOCKED;
		}
	}
	else
	{
		// since there is no collision the piece may continue its travel
		// to the ground...
		pPl->nRow++;

		// are we gliding?
		pPl->status = tetris_playfield_hoverStatus(pPl);
	}
}


/* Function:           tetris_playfield_movePiece
 * Description:        moves piece to the given direction
 * Argument pPl:       playfield to perform action on
 * Argument direction: direction (see tetris_playfield_direction_t)
 * Return value:       1 if piece could be moved, 0 otherwise
 */
uint8_t tetris_playfield_movePiece(tetris_playfield_t *pPl,
                                   tetris_playfield_direction_t direction)
{
	assert(pPl != NULL);

	// a piece can only be moved if it is still hovering or gliding
	assert((pPl->status == TETRIS_PFS_HOVERING) ||
		(pPl->status == TETRIS_PFS_GLIDING));

	int8_t nOffset = (direction == TETRIS_PFD_LEFT) ? -1 : 1;
	if (tetris_playfield_collision(pPl, pPl->nColumn + nOffset, pPl->nRow) == 0)
	{
		pPl->nColumn += nOffset;

		// are we gliding?
		pPl->status = tetris_playfield_hoverStatus(pPl);
		return 1;
	}

	return 0;
}


/* Function:     tetris_playfield_rotatePiece
 * Description:  rotates piece to the given direction
 * Argument pPl: playfield to perform action on
 * Argument r:   type of rotation (see tetris_piece_rotation_t)
 * Return value: 1 if piece could be rotated, 0 otherwise
 */
uint8_t tetris_playfield_rotatePiece(tetris_playfield_t *pPl,
                                     tetris_piece_rotation_t rotation)
{
	assert(pPl != NULL);

	// a piece can only be rotation if it is still hovering or gliding
	assert((pPl->status == TETRIS_PFS_HOVERING) ||
			(pPl->status == TETRIS_PFS_GLIDING));

	tetris_piece_rotate(pPl->pPiece, rotation);

	// does the rotated piece cause a collision?
	if (tetris_playfield_collision(pPl, pPl->nColumn, pPl->nRow) != 0)
	{
		// in that case we revert the rotation
		if (rotation == TETRIS_PC_ROT_CW)
		{
			tetris_piece_rotate(pPl->pPiece, TETRIS_PC_ROT_CCW);
		}
		else
		{
			tetris_piece_rotate(pPl->pPiece, TETRIS_PC_ROT_CW);
		}

		return 0;
	}

	// are we gliding?
	pPl->status = tetris_playfield_hoverStatus(pPl);

	return 1;
}


/* Function:     tetris_playfield_removeCompletedLines
 * Description:  removes completed lines (if any) and lowers the dump
 * Argument pPl: playfield to perform action on
 * Return value: void
 */
void tetris_playfield_removeCompleteLines(tetris_playfield_t *pPl)
{
	assert(pPl != NULL);

	// rows can only be removed if we are in state TETRIS_PFS_DOCKED
	assert(pPl->status == TETRIS_PFS_DOCKED);

	// bit mask of a full row
	uint16_t nFullRow = 0xFFFF >> (16 - pPl->nWidth);

	// bit mask (only 4 bits) that tells us if the n-th row after the
	// current nRow is complete (n-th bit set to 1, LSB represents nRow itself)
	uint8_t nRowMask = 0;

	// determine sane start and stop values for the dump' index
	int8_t nStartRow =
		((pPl->nRow + 3) >= pPl->nHeight) ? pPl->nHeight - 1 : pPl->nRow + 3;
	int8_t nStopRow = (pPl->nRow < 0) ? 0 : pPl->nRow;

	// dump index variables
	//   for incomplete rows, both variables will be decremented
	//   for complete rows, only i gets decremented
	int8_t nLowestRow = nStartRow;

	// save old value for the first dump index with matter
	int8_t nFormerFirstMatterRow = pPl->nFirstMatterRow;

	// this loop only considers rows which are affected by the piece
	for (int8_t i = nStartRow; i >= nStopRow; --i)
	{
		// is current row a full row?
		if ((nFullRow & pPl->dump[i]) == nFullRow)
		{
			// adjust value for the highest row with matter
			pPl->nFirstMatterRow++;

			// set corresponding bit for the row mask
			// nRowMask |= 0x08 >> (nStartRow - i);
			nRowMask |= 0x01 <<  (i - pPl->nRow);
		}
		else
		{
			// if nLowestRow and i differ, the dump has to be shifted
			if (i < nLowestRow)
			{
				pPl->dump[nLowestRow] = pPl->dump[i];
			}
			--nLowestRow;
		}
	}

	// if rows have been removed, this loop shifts the rest of the dump
	uint8_t nComplete = nLowestRow - nStopRow + 1;
	if (nComplete > 0)
	{
		for (int8_t i = nStopRow - 1; nLowestRow >= nFormerFirstMatterRow; --i)
		{
			// is the row we are copying from below the upper border?
			if (i >= nFormerFirstMatterRow)
			{
				// just copy from that row
				pPl->dump[nLowestRow] = pPl->dump[i];
			}
			else
			{
				// rows above the upper border are always empty
				pPl->dump[nLowestRow] = 0;
			}
			--nLowestRow;
		}
	}

	// ready to get the next piece
	pPl->status = TETRIS_PFS_READY;

	pPl->nRowMask = nRowMask;
}


/*****************
 * get functions *
 *****************/

/* Function:     tetris_playfield_getWidth
 * Description:  returns the width of the playfield
 * Argument pPl: the playfield we want information from
 * Return value: width of the playfield
 */
int8_t tetris_playfield_getWidth(tetris_playfield_t *pPl)
{
	assert(pPl != NULL);
	return pPl->nWidth;
}


/* Function:     tetris_playfield_getHeight
 * Description:  returns the height of the ayfield we want information from
 * Return value: height of the playfield
 */
int8_t tetris_playfield_getHeight(tetris_playfield_t *pPl)
{
	assert(pPl != NULL);
	return pPl->nHeight;
}


/* Function:     tetris_playfield_getPiece
 * Description:  returns the currently falling piece
 * Argument pPl: the playfield we want information from
 * Return value: pointer to the currently falling piece
 */
tetris_piece_t *tetris_playfield_getPiece(tetris_playfield_t *pPl)
{
	assert(pPl != NULL);
	return pPl->pPiece;
}


/* Function:     tetris_playfield_getColumn
 * Description:  returns the column of the currently falling piece
 * Argument pPl: the playfield we want information from
 * Return value: column of the currently falling piece
 */
int8_t tetris_playfield_getColumn(tetris_playfield_t *pPl)
{
	assert(pPl != NULL);
	return pPl->nColumn;
}


/* Function:     tetris_playfield_getRow
 * Description:  returns the row of the currently falling piece
 * Argument pPl: the playfield we want information from
 * Return value: row of the currently falling piece
 */
int8_t tetris_playfield_getRow(tetris_playfield_t *pPl)
{
	assert(pPl != NULL);
	return pPl->nRow;
}


/* Function:     tetris_playfield_getRowMask
 * Description:  returns the row mask relative to nRow
 * Argument pPl: the playfield we want information from
 * Return value: the first 4 bits indicate which lines (relative to nRow)
 *               have been removed if we are in status TETRIS_PFS_READY
 *               LSB is the highest line
 */
uint8_t tetris_playfield_getRowMask(tetris_playfield_t *pPl)
{
	assert(pPl != NULL);
	return pPl->nRowMask;
}


/* Function:     tetris_playfield_getStatus
 * Description:  returns the status of the playfield
 * Argument pPl: the playfield we want information from
 * Return value: status of the playfield (see tetris_playfield_status_t)
 */
tetris_playfield_status_t tetris_playfield_getStatus(tetris_playfield_t *pPl)
{
	assert(pPl != NULL);
	return pPl->status;
}


/* Function:      tetris_playfield_getDumpRow
 * Description:   returns the given row of the dump (as bitmap)
 * Argument pPl:  the playfield we want information from
 * Argument nRow: the number of the row (0 <= nRow < height of playfield)
 * Return value:  bitmap of the requested row (LSB is leftmost column)
 */
uint16_t tetris_playfield_getDumpRow(tetris_playfield_t *pPl,
                                     int8_t nRow)
{
	assert(pPl != NULL);
	assert((0 <= nRow) && (nRow < pPl->nHeight));
	return pPl->dump[nRow];
}


#ifdef GAME_BASTET

/* Function:         tetris_playfield_predictDeepestRow
 * Description:      returns the deepest possible row of a given piece
 * Argument pPl:     the playfield on which we want to test a piece
 * Argument pPiece:  the piece which should be tested
 * Argument nColumn: the column where the piece should be dropped
 * Return value:     the row of the piece (playfield compliant coordinates)
 */
int8_t tetris_playfield_predictDeepestRow(tetris_playfield_t *pPl,
                                          tetris_piece_t *pPiece,
                                          int8_t nColumn)
{
	int8_t nRow = tetris_playfield_getPieceStartPos(pPiece);
	tetris_piece_t *pActualPiece  = pPl->pPiece;
	pPl->pPiece = pPiece;

	// is it actually possible to use this piece?
	if (tetris_playfield_collision(pPl, (pPl->nWidth - 2) / 2, nRow) ||
			(tetris_playfield_collision(pPl, nColumn, nRow)))
	{
		// restore real piece
		pPl->pPiece = pActualPiece;

		return -4;
	}

	// determine deepest row
	nRow = (nRow < pPl->nFirstMatterRow - 4) ? pPl->nFirstMatterRow - 4 : nRow;
	while ((nRow < pPl->nHeight) &&
			(!tetris_playfield_collision(pPl, nColumn, nRow + 1)))
	{
			++nRow;
	}

	// restore real piece
	pPl->pPiece = pActualPiece;

	return nRow;
}

/* Function:         tetris_playfield_predictCompleteLines
 * Description:      predicts the number of complete lines for a piece at
 *                   a given column
 * Argument pPl:     the playfield on which we want to test a piece
 * Argument pPiece:  the piece which should be tested
 * Argument nRow:    the row where the given piece collides
 * Argument nColumn: the column where the piece should be dropped
 * Return value:     amount of complete lines
 */
int8_t tetris_playfield_predictCompleteLines(tetris_playfield_t *pPl,
                                             tetris_piece_t *pPiece,
                                             int8_t nRow,
                                             int8_t nColumn)
{
	int8_t nCompleteRows = 0;

	// bit mask of a full row
	uint16_t nFullRow = 0xFFFF >> (16 - pPl->nWidth);

	if (nRow > -4)
	{
		// determine sane start and stop values for the dump's index
		int8_t nStartRow =
			((nRow + 3) >= pPl->nHeight) ? pPl->nHeight - 1 : nRow + 3;
		int8_t nStopRow = (nRow < 0) ? 0 : nRow;

		uint16_t nPiece = tetris_piece_getBitmap(pPiece);

		for (int8_t i = nStartRow; i >= nStopRow; --i)
		{
			int8_t y = i - nRow;

			// clear all bits of the piece we are not interested in and
			// align the rest to LSB
			uint16_t nPieceMap = (nPiece & (0x000F << (y << 2))) >> (y << 2);
			// shift the remaining content to the current column
			if (nColumn >= 0)
			{
				nPieceMap <<= nColumn;
			}
			else
			{
				nPieceMap >>= -nColumn;
			}
			// embed piece in dump map
			uint16_t nDumpMap = pPl->dump[i] | nPieceMap;

			// is current row a full row?
			if ((nFullRow & nDumpMap) == nFullRow)
			{
				++nCompleteRows;
			}
		}
	}

	return nCompleteRows;
}


/* Function:         tetris_playfield_predictBottomRow
 * Description:      predicts the appearance of the bottom row of the
 *                   playfield (for a piece at a given column) and
 *                   initializes an iterator structure
 * Argument pIt:     [out] a pointer to an iterator which should be initialized
 * Argument pPl:     the playfield on which we want to test a piece
 * Argument pPiece:  the piece which should be tested
 * Argument nRow:    the row where the given piece collides
 * Argument nColumn: the column where the piece should be dropped
 * Return value:     appearance of the predicted dump row at the bottom
 */
uint16_t* tetris_playfield_predictBottomRow(tetris_playfield_iterator_t *pIt,
                                            tetris_playfield_t *pPl,
                                            tetris_piece_t *pPiece,
                                            int8_t nRow,
                                            int8_t nColumn)
{
	pIt->pPlayfield = pPl;
	pIt->pPiece = pPiece;
	pIt->nColumn = nColumn;
	pIt->nFullRow = 0xFFFF >> (16 - pPl->nWidth);
	pIt->nCurrentRow = pPl->nHeight - 1;
	pIt->nRowBuffer = 0;

	// determine sane start and stop values for the piece's row indices
	pIt->nPieceHighestRow = nRow;
	pIt->nPieceLowestRow = ((pIt->nPieceHighestRow + 3) < pPl->nHeight) ?
			(pIt->nPieceHighestRow + 3) : pPl->nHeight - 1;

	// don't return any trailing rows which are empty, so we look for a stop row
	pIt->nStopRow = pPl->nFirstMatterRow < nRow ? pPl->nFirstMatterRow : nRow;
	pIt->nStopRow = pIt->nStopRow < 0 ? 0 : pIt->nStopRow;

	return tetris_playfield_predictNextRow(pIt);
}


/* Function:         tetris_playfield_predictNextRow
 * Description:      predicts the appearance of the next row of the playfield
 *                   (for a given iterator)
 * Argument pIt:     a pointer to a dump iterator
 * Return value:     appearance of next predicted row (or NULL -> no next line)
 */
uint16_t* tetris_playfield_predictNextRow(tetris_playfield_iterator_t *pIt)
{
	uint16_t nPieceMap = 0;

	if ((pIt->nPieceHighestRow > -4) && (pIt->nCurrentRow >= pIt->nStopRow))
	{
		uint16_t nPiece = tetris_piece_getBitmap(pIt->pPiece);

		if ((pIt->nCurrentRow <= pIt->nPieceLowestRow) &&
				(pIt->nCurrentRow >= pIt->nPieceHighestRow))
		{
			int8_t y = pIt->nCurrentRow - pIt->nPieceHighestRow;

			// clear all bits of the piece we are not interested in and
			// align the rest to LSB
			nPieceMap = (nPiece & (0x000F << (y << 2))) >> (y << 2);
			// shift the remaining content to the current column
			if (pIt->nColumn >= 0)
			{
				nPieceMap <<= pIt->nColumn;
			}
			else
			{
				nPieceMap >>= -pIt->nColumn;
			}
		}

		pIt->nRowBuffer = pIt->pPlayfield->dump[pIt->nCurrentRow--] | nPieceMap;
		// don't return full (and therefore removed) rows
		if (pIt->nRowBuffer == pIt->nFullRow)
		{
			// recursively determine next (?) row instead
			return tetris_playfield_predictNextRow(pIt);
		}
		// row isn't full
		else
		{
			return &pIt->nRowBuffer;
		}
	}
	else
	{
		return NULL;
	}
}

#endif /* GAME_BASTET */