core: Re-arrange internal implementation of 'pixelDissolve()'.
This commit is contained in:
iwannabethedev
Nathan Adams
parent
deae231176
commit
0f30b378b0
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@ -1618,68 +1618,6 @@ pub fn set_pixels_from_byte_array<'gc>(
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Ok(())
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}
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/// Returns at least 2. Always returns an even number.
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fn get_feistel_block_size(sequence_length: u32) -> u32 {
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let sequence_length = sequence_length.max(2);
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// For the given sequence length, figure out the number of bits required to
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// represent all indices for the sequence. After that, round up to
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// the nearest even number of bits.
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// For instance, for a sequence of length 9, 4 bits are required,
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// and 4 is even, so the result is 4.
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// For a sequence of length 8, 3 bits are required, but 3 is not
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// even, so round up to 4.
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let mut bit_number: u32 = 0;
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let mut num = sequence_length - 1;
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while num > 0 {
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num /= 2;
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bit_number += 1;
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}
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bit_number + (bit_number % 2)
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}
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/// Meant to be a bijective function that takes a raw index and gives the corresponding
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/// Feistel index.
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///
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/// # Arguments
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///
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/// * `raw_permutation_index` - Must obey '0 <= permutation_raw_index < permutation_length`.
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/// * `feistel_block_size` - See `get_feistel_block_size()`.
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fn pixel_dissolve_raw_to_feistel_index(raw_permutation_index: u32, feistel_block_size: u32) -> u32 {
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// Discussion on Feistel networks:
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// https://github.com/ruffle-rs/ruffle/issues/10962
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// For the simple balanced variant of a Feistel network, an even number of
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// bits for the block size is required (unbalanced Feistel networks
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// also exists, but are presumably more complex).
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// Applying a single round of Feistel.
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let feistel_halfpiece_size = feistel_block_size / 2;
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let halfpiece1 = raw_permutation_index >> feistel_halfpiece_size;
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let halfpiece2 = raw_permutation_index & ((1 << feistel_halfpiece_size) - 1);
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// Apply some function to make the output appear more random.
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// TODO: It would be good to test and improve this heuristic function for creating
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// random-looking output. One possibility is some decent but fast PRNG. The function can
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// also take `feistel_block_size` as an argument.
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// This specific function was gotten by trial-and-error on what might make the output look
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// random.
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fn f(num: u32) -> u32 {
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num * num + 1
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}
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let result_before_xor = (f(halfpiece2)) % (1 << feistel_halfpiece_size);
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let new_halfpiece1 = halfpiece2;
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let new_halfpiece2 = halfpiece1 ^ result_before_xor;
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(new_halfpiece2 << feistel_halfpiece_size) | new_halfpiece1
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}
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#[allow(clippy::too_many_arguments)]
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pub fn pixel_dissolve<'gc>(
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mc: MutationContext<'gc, '_>,
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@ -1691,6 +1629,101 @@ pub fn pixel_dissolve<'gc>(
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num_pixels: i32,
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fill_color: i32,
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) -> i32 {
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/// Returns at least 2. Always returns an even number.
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fn get_feistel_block_size(sequence_length: u32) -> u32 {
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let sequence_length = sequence_length.max(2);
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// For the given sequence length, figure out the number of bits required to
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// represent all indices for the sequence. After that, round up to
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// the nearest even number of bits.
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// For instance, for a sequence of length 9, 4 bits are required,
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// and 4 is even, so the result is 4.
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// For a sequence of length 8, 3 bits are required, but 3 is not
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// even, so round up to 4.
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let mut bit_number: u32 = 0;
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let mut num = sequence_length - 1;
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while num > 0 {
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num /= 2;
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bit_number += 1;
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}
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bit_number + (bit_number % 2)
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}
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/// Meant to be a bijective function that takes a raw index and gives the corresponding
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/// Feistel index.
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///
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/// # Arguments
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///
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/// * `raw_permutation_index` - Must obey '0 <= permutation_raw_index < permutation_length`.
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/// * `feistel_block_size` - See `get_feistel_block_size()`.
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fn pixel_dissolve_raw_to_feistel_index(
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raw_permutation_index: u32,
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feistel_block_size: u32,
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) -> u32 {
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// Discussion on Feistel networks:
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// https://github.com/ruffle-rs/ruffle/issues/10962
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// For the simple balanced variant of a Feistel network, an even number of
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// bits for the block size is required (unbalanced Feistel networks
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// also exists, but are presumably more complex).
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// Applying a single round of Feistel.
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let feistel_halfpiece_size = feistel_block_size / 2;
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let halfpiece1 = raw_permutation_index >> feistel_halfpiece_size;
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let halfpiece2 = raw_permutation_index & ((1 << feistel_halfpiece_size) - 1);
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// Apply some function to make the output appear more random.
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// TODO: It would be good to test and improve this heuristic function for creating
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// random-looking output. One possibility is some decent but fast PRNG. The function can
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// also take `feistel_block_size` as an argument.
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// This specific function was gotten by trial-and-error on what might make the output look
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// random.
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fn f(num: u32) -> u32 {
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num * num + 1
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}
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let result_before_xor = (f(halfpiece2)) % (1 << feistel_halfpiece_size);
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let new_halfpiece1 = halfpiece2;
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let new_halfpiece2 = halfpiece1 ^ result_before_xor;
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(new_halfpiece2 << feistel_halfpiece_size) | new_halfpiece1
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}
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fn write_pixel(
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write: &mut RefMut<BitmapData>,
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different_source_than_target: &Option<Ref<BitmapData>>,
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fill_color: i32,
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transparency: bool,
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base_point: (u32, u32),
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read_offset: (u32, u32),
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write_offset: (u32, u32),
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) {
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let read_point = (read_offset.0 + base_point.0, read_offset.1 + base_point.1);
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let write_point = (write_offset.0 + base_point.0, write_offset.1 + base_point.1);
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match different_source_than_target {
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None => {
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write.set_pixel32_raw(
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write_point.0,
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write_point.1,
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Color::from(fill_color).to_premultiplied_alpha(transparency),
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);
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}
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Some(different_source) => {
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write.set_pixel32_raw(
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write_point.0,
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write_point.1,
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different_source.get_pixel32_raw(read_point.0, read_point.1),
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);
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}
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}
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}
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// Apparently,
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// "numPixels:int (default = 0) — The default is 1/30 of the source area (width x height). "
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// is wrong.
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@ -1727,36 +1760,6 @@ pub fn pixel_dissolve<'gc>(
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let write_offset = (dest_region.x_min, dest_region.y_min);
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let read_offset = (source_region.x_min, source_region.y_min);
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fn write_pixel(
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write: &mut RefMut<BitmapData>,
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different_source_than_target: &Option<Ref<BitmapData>>,
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fill_color: i32,
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transparency: bool,
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base_point: (u32, u32),
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read_offset: (u32, u32),
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write_offset: (u32, u32),
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) {
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let read_point = (read_offset.0 + base_point.0, read_offset.1 + base_point.1);
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let write_point = (write_offset.0 + base_point.0, write_offset.1 + base_point.1);
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match different_source_than_target {
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None => {
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write.set_pixel32_raw(
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write_point.0,
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write_point.1,
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Color::from(fill_color).to_premultiplied_alpha(transparency),
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);
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}
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Some(different_source) => {
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write.set_pixel32_raw(
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write_point.0,
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write_point.1,
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different_source.get_pixel32_raw(read_point.0, read_point.1),
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);
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}
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}
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}
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let different_source_than_target = if source_bitmap.ptr_eq(target) {
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None
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} else {
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