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78 lines
3.4 KiB
Text
78 lines
3.4 KiB
Text
Duh, an 'easy' way to replicate Giess's behavior:
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For each frame, you have to mutate it by a transform matrix. This is
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easy, thought not cheap. First you precalculate the transform matrix how
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you want it, based on whatever rotations or whatever you want.
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The data stored in each spot on the matrix tells you how to transform a
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single pixel. The simple case is dx,dy, where both are relatively small.
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The probably ought to be a byte in any case, so you can scale the
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transform matrix on slow machines. A more complex case is some trick
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whereby a single pixel ends up splattered in several places. Idea below.
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The matrix consists of some number of 8bit arrays of the same size as the
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image. They'd probably be line-interleaved or better to help with cache
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effects (which are VERY serious here). Each channel represents some
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aspect of the transform. The first two would likely be dx and dy, the
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third might be a multiplier if that wasn't done statically.
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The idea: any number of transform sets could be applied, given available
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processing power. Just set the static scalar or the multiplier matrices
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so you don't completely swamp the output pixels.
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Note that this is fastest in 8-bit, but theoretically could be applied to
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32 bit. 15 and 16 are hard, since you can't easily apply the multipliers
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unless they're 1/2^n, and even then it's significantly heavier (you'd have
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to mask the top n bits of each color out).
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This SCREAMS for MMX, in case you haven't figured it out yet.
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Unfortunatley, MMX is only directly useful for the scalar matrix, unless
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you do a trick where all the pixels in that fit in 64 bits (8 8bit, 4
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16bit, or 2 32bit) are always moved in a group. This is very possible,
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and might be a significant perf increase by being able to use MMX all the
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way through. Otherwise you have to place each pixel by extracting the MMX
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stuff back into normal registers, and that just plain sucks.
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A pseudo-C implementation:
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----- BEGIN -----
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gint x,y; /* image x and y size */
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guchar old_image[x][y]; /* original image */
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guchar new_image[x][y]; /* new image */
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gchar x_xform[x][y]; /* dx matrix */
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gchar y_xform[x][y]; /* dy matrix */
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guchar s_xform[x][y]; /* intensity scalar matrix */
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guchar scalar; /* global scalar */
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gint i,j; /* indixes */
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gulong p; /* pixel value in question */
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guchar u,v,w; /* modifier variables */
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/* clear the new image, we don't want anything getting in the way */
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/* NOT NECESSARILY A GOOD THING, THOUGH */
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memset(new_image,0,x*y);
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/* loop through all the lines in the image */
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for (j=0;j<y;j++) {
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/* loop through all the pixels in the line */
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for (i=0;i<x;i++) {
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p = old_image[i][j];
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u = x_xform[i][j];
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v = y_xform[i][j];
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w = s_xform[i][j];
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new_image[i+u][j+v] = (guchar)((p<<14) / (w * scalar));
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}
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}
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----- END -----
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Note that the above really, *REALLY* sucks performance-wise. Throw it a
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80x60 image and it'll swamp my poor laptop. Also note that I simply set
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the pixel value, not merge it. That means you'd better be sure your
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transform matrix doesn't have overlapping destinations.
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Other notes about the above code: x_xform and y_xform are signed chars,
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which means pixels can move in all directions. The intensity matrix is
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unsigned, with a range from 0 to 255, so is the global scalar. Note the
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shift of 14bits (2 * 7bits), then divide by each. That means identity for
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both scalars is at 128. The FP range of each is thus 0.0 to 2.0. Very
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handy.
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