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An fast realtime interactive fractal zoomer

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3.4.3 Moving Pixels to New Positions

Since XaoS is using the approximation algorithm the following table is filled for every row/column:

calculate is 1 if the current row/column is new and needs to be calculated or 0 if no old pixels need to be moved. oldpoint is a pointer to the old row/column that corresponds to the new one. This pixel needs to be copied to the new location. position is the real and imaginary components of the coordinates used for future approximations. Because almost all points will be moved, the solution seems to be simple: for every new point look at the row and column table; copy it if required.

There is the problem that this minimally needs three memory reads for every pixel (read calculate, oldpoint and index of old point). This is too slow, so a small optimization is performed. Instead rewriting the piece of code in assembly, normal memcpy is used to move blocks of pixels to their new locations. This minimizes the internal loop and access can be done more quickly since memcpy is usually optimized for each architecture.

Using the row table, a list of blocks to move for every row is created. With this new table all the pixels can be moved quickly. This increased the speed of XaoS about four times and made this function so fast that it is no longer a problem. (In fact, it takes much less processing than all other parts of XaoS.)

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