23 lines
1.1 KiB
Dart
23 lines
1.1 KiB
Dart
/// Converts an index of a set size to the corresponding index of a collection of another size
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/// as if they were circular.
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///
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/// Takes a [position] from collection Foo, a [base] from where Foo's index originated
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/// and the [length] of a second collection Baa, for which the correlating index is sought.
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///
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/// For example; We have a Carousel of 10000(simulating infinity) but only 6 images.
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/// We need to repeat the images to give the illusion of a never ending stream.
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/// By calling _getRealIndex with position and base we get an offset.
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/// This offset modulo our length, 6, will return a number between 0 and 5, which represent the image
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/// to be placed in the given position.
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int getRealIndex(int position, int base, int? length) {
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final int offset = position - base;
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return remainder(offset, length);
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}
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/// Returns the remainder of the modulo operation [input] % [source], and adjust it for
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/// negative values.
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int remainder(int input, int? source) {
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if (source == 0) return 0;
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final int result = input % source!;
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return result < 0 ? source + result : result;
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} |