borgware-2d/animations/bitmapscroller.c

#include <stdlib.h>
#include <stdint.h>
#include <assert.h>

#include "../random/prng.h"
#include "../util.h"
#include "../autoconf.h"
#include "../pixel.h"
#include "bitmapscroller.h"


/**
 * This structure merely contains the meta data of the bitmap. The actual
 * bitmap data is delivered by a user provided function.
 */
typedef struct bitmap_t
{
	unsigned int nWidth;          /**< Width of the bitmap. */
	unsigned int nHeight;         /**< Height of the bitmap. */
	unsigned char nBitPlanes;     /**< Number of bit planes. */
	bitmap_getChunk_t fpGetChunk; /**< Bitmap chunk retrieving function. */
	unsigned int nFrame;          /**< Current frame number. */
	unsigned int nViewportWidth;  /**< Width of the displayed content. */
	unsigned int nViewportHeight; /**< Height of the displayed content. */
	unsigned int nXDomain;        /**< Last valid x-coordinate for viewport. */
	unsigned int nYDomain;        /**< Last valid y-coordinate for viewport. */
	unsigned int nChunkDomain;    /**< Last valid chunk for viewport. */
	unsigned int nChunkCount;     /**< Amount of horiz. chunks of the bitmap. */
}
bitmap_t;


/**
 * This function generates an eight-by-one pixel chunk for a given pair of pixel
 * coordinates and a borg plane number. The resulting chunk can be copied
 * directly to the borg's frame buffer. It makes use of the user provided
 * "getChunk" function which in contrast only accepts chunk based coordinates
 * (resulting in chunks whose x-coordinates are always a multiple of eight) and
 * uses bit planes which defer from the plane scheme used by the borg's frame
 * buffer.
 * @param pBitmap The bitmap of interest.
 * @param nBorgPlane The nunmber of the borg plane of interest.
 * @param x x-coordinate of the bitmap
 * @param y y-coordinate of the bitmap
 * @return The bitmap chunk packed into an unsigned char.
 */
static unsigned char bitmap_getAlignedChunk(bitmap_t const *const pBitmap,
                                            unsigned char const nBorgPlane,
                                            unsigned int const x,
                                            unsigned int const y)
{
	assert(x <= pBitmap->nChunkDomain);
	assert(y < pBitmap->nHeight);

	unsigned char nChunk = 0xFF;
	unsigned char nMask = 1;
	unsigned char nAlignment = x % 8;

	// we have to go through every bit plane
	for (int i = 0; i < pBitmap->nBitPlanes; ++i)
	{
		// generate chunk
		unsigned char nPlaneChunk;
		// if the given x-coordinate is aligned to a chunk coordinate we can
		// reuse the result of the "getChunk" function directly.
		if (nAlignment == 0)
		{
			nPlaneChunk = pBitmap->fpGetChunk(i, x/8, y, pBitmap->nFrame);
		}
		// in case of misalignment we combine two chunks with chunk based
		// coordinates into one chunk which aligns to the given x-coordinate
		else
		{
			nPlaneChunk = pBitmap->fpGetChunk(i, x/8, y, pBitmap->nFrame)
					<< nAlignment;
			nPlaneChunk |= pBitmap->fpGetChunk(i, x/8+1, y, pBitmap->nFrame)
					>> (8 - nAlignment);
		}

		// convert the bit plane information into the borg plane format
		nChunk &= ((nBorgPlane + 1) & nMask) == 0 ? ~nPlaneChunk : nPlaneChunk;
		nMask <<= 1;
	}

	return nChunk;
}


/**
 * This function actually draws the bitmap onto the screen. The viewport is
 * @param pBitmap The bitmap which shall be shown.
 * @param nX The x-coordinate of the bitmap which shall be displayed at the top
 *           left of the viewport.
 * @param nY The y-coordinate of the bitmap which shall be displayed at the top
 *           left of the viewport.
 */
static void bitmap_drawViewport(bitmap_t const *const pBitmap,
                                unsigned int const nX,
                                unsigned int const nY)
{
	assert(nX <= pBitmap->nXDomain);
	assert(nY <= pBitmap->nYDomain);
	unsigned char nBitmapHwPlanes = (1 << pBitmap->nBitPlanes) - 1;
	unsigned char nPlanes = nBitmapHwPlanes > NUMPLANE ?
			NUMPLANE : nBitmapHwPlanes;

	for (int8_t y = 0; y < pBitmap->nViewportHeight; ++y)
	{
		for (int8_t x = pBitmap->nViewportWidth; x > 0; x -= 8)
		{
			for (int8_t p = NUMPLANE - nPlanes; p < NUMPLANE; ++p)
			{
				uint8_t nChunk;
				if ((nX + x - 8) >= 0)
				{
					nChunk = bitmap_getAlignedChunk(pBitmap, p, nX+x-8, nY + y);
					pixmap[p][y][pBitmap->nChunkCount - 1 - ((x-1)/8)] = nChunk;
				}
				else
				{
					nChunk = bitmap_getAlignedChunk(pBitmap, p, nX, nY + y)
							>> (8-x);
					pixmap[p][y][pBitmap->nChunkCount - 1] = nChunk;
				}
			}
		}
	}
}


/**
 * This functions calculates randomly chosen offsets to move the viewport
 * accross the bitmap.
 * @param pBitmap The bitmap of interest.
 * @param x The current x-coordinate of the viewport.
 * @param y The current y-coordinate of the viewport.
 * @param pdx Pointer to a variable which shall hold the horizontal offset.
 * @param pdy Pointer to a variable which shall hold the vertical offset.
 */
static void bitmap_recalculateVector(bitmap_t const *const pBitmap,
                                     unsigned int const x,
                                     unsigned int const y,
                                     char *const pdx,
                                     char *const pdy)
{
	if (((x + *pdx) > (pBitmap->nXDomain)) || ((x + *pdx) < 0))
	{
		*pdx = random8() % 2 * (x < (pBitmap->nXDomain / 2) ? 1 : -1);
	}
	if (((y + *pdy) > (pBitmap->nYDomain)) || ((y + *pdy) < 0))
	{
		*pdy = random8() % 2 * (y < (pBitmap->nYDomain / 2) ? 1 : -1);
	}
	if (*pdx == 0 && *pdy == 0)
	{
		*pdx = (x < (pBitmap->nXDomain / 2) ? 1 : -1);
		*pdy = (y < (pBitmap->nYDomain / 2) ? 1 : -1);
	}
}


/**
 * This function scrolls through a bitmap.
 * @param nWidth Width of the bitmap.
 * @param nHeight Height of bitmap.
 * @param nBitPlanes Amount of bit planes.
 * @param nFrameCount How many frames shall be shown.
 * @param nFrameTick Duration of a displayed frame in milliseconds.
 * @param fpGetChunk Function that returns an eight-by-one chunk of a bitmap.
 */
void bitmap_scroll(unsigned int const nWidth,
                   unsigned int const nHeight,
                   unsigned char const nBitPlanes,
                   unsigned int const nFrameCount,
                   unsigned int const nFrameTick,
                   bitmap_getChunk_t fpGetChunk)
{
	assert((nBitPlanes > 0) && (nBitPlanes <= 8));

	bitmap_t bitmap;

	// user provided values
	bitmap.nWidth = nWidth;
	bitmap.nHeight = nHeight;
	bitmap.nBitPlanes = nBitPlanes;
	bitmap.fpGetChunk = fpGetChunk;

	// calculate domains for coordinates and chunk indices
	bitmap.nViewportWidth = (NUM_COLS > nWidth) ? nWidth : NUM_COLS;
	bitmap.nViewportHeight = (NUM_ROWS > nHeight) ? nHeight : NUM_ROWS;
	bitmap.nXDomain = nWidth - bitmap.nViewportWidth;
	bitmap.nYDomain = nHeight - bitmap.nViewportHeight;
	bitmap.nChunkDomain = nWidth - 8;
	bitmap.nChunkCount = (((bitmap.nViewportWidth - 1) / 8) + 1);

	// initial starting point
	int x = random8() % (bitmap.nXDomain + 1);
	int y = random8() % (bitmap.nYDomain + 1);
	char dx = 0;
	char dy = 0;

	// remove garbage from screen
	clear_screen(0);

	for (bitmap.nFrame = 0; bitmap.nFrame < nFrameCount; ++bitmap.nFrame)
	{
		bitmap_drawViewport(&bitmap, x, y);

		bitmap_recalculateVector(&bitmap, x, y, &dx, &dy);
		x += bitmap.nWidth > bitmap.nViewportWidth ? dx : 0;
		y += bitmap.nHeight > bitmap.nViewportHeight ? dy : 0;

		wait(nFrameTick);
	}
}