core: Re-arrange internal implementation of 'pixelDissolve()'.

core/src/bitmap/operations.rs

@@ -1618,8 +1618,19 @@ pub fn set_pixels_from_byte_array<'gc>(
     Ok(())
 }
 
-/// Returns at least 2. Always returns an even number.
+#[allow(clippy::too_many_arguments)]
-fn get_feistel_block_size(sequence_length: u32) -> u32 {
+pub fn pixel_dissolve<'gc>(
+    mc: MutationContext<'gc, '_>,
+    target: BitmapDataWrapper<'gc>,
+    source_bitmap: BitmapDataWrapper<'gc>,
+    src_rect: (i32, i32, i32, i32),
+    dest_point: (i32, i32),
+    random_seed: i32,
+    num_pixels: i32,
+    fill_color: i32,
+) -> i32 {
+    /// Returns at least 2. Always returns an even number.
+    fn get_feistel_block_size(sequence_length: u32) -> u32 {
         let sequence_length = sequence_length.max(2);
 
         // For the given sequence length, figure out the number of bits required to
@@ -1639,16 +1650,19 @@ fn get_feistel_block_size(sequence_length: u32) -> u32 {
         }
 
         bit_number + (bit_number % 2)
-}
+    }
 
-/// Meant to be a bijective function that takes a raw index and gives the corresponding
+    /// Meant to be a bijective function that takes a raw index and gives the corresponding
-/// Feistel index.
+    /// Feistel index.
-///
+    ///
-/// # Arguments
+    /// # Arguments
-///
+    ///
-/// * `raw_permutation_index` - Must obey '0 <= permutation_raw_index < permutation_length`.
+    /// * `raw_permutation_index` - Must obey '0 <= permutation_raw_index < permutation_length`.
-/// * `feistel_block_size` - See `get_feistel_block_size()`.
+    /// * `feistel_block_size` - See `get_feistel_block_size()`.
-fn pixel_dissolve_raw_to_feistel_index(raw_permutation_index: u32, feistel_block_size: u32) -> u32 {
+    fn pixel_dissolve_raw_to_feistel_index(
+        raw_permutation_index: u32,
+        feistel_block_size: u32,
+    ) -> u32 {
         // Discussion on Feistel networks:
         // https://github.com/ruffle-rs/ruffle/issues/10962
 
@@ -1678,19 +1692,38 @@ fn pixel_dissolve_raw_to_feistel_index(raw_permutation_index: u32, feistel_block
         let new_halfpiece2 = halfpiece1 ^ result_before_xor;
 
         (new_halfpiece2 << feistel_halfpiece_size) | new_halfpiece1
-}
+    }
 
-#[allow(clippy::too_many_arguments)]
+    fn write_pixel(
-pub fn pixel_dissolve<'gc>(
+        write: &mut RefMut<BitmapData>,
-    mc: MutationContext<'gc, '_>,
+        different_source_than_target: &Option<Ref<BitmapData>>,
-    target: BitmapDataWrapper<'gc>,
-    source_bitmap: BitmapDataWrapper<'gc>,
-    src_rect: (i32, i32, i32, i32),
-    dest_point: (i32, i32),
-    random_seed: i32,
-    num_pixels: i32,
         fill_color: i32,
-) -> i32 {
+        transparency: bool,
+        base_point: (u32, u32),
+        read_offset: (u32, u32),
+        write_offset: (u32, u32),
+    ) {
+        let read_point = (read_offset.0 + base_point.0, read_offset.1 + base_point.1);
+        let write_point = (write_offset.0 + base_point.0, write_offset.1 + base_point.1);
+
+        match different_source_than_target {
+            None => {
+                write.set_pixel32_raw(
+                    write_point.0,
+                    write_point.1,
+                    Color::from(fill_color).to_premultiplied_alpha(transparency),
+                );
+            }
+            Some(different_source) => {
+                write.set_pixel32_raw(
+                    write_point.0,
+                    write_point.1,
+                    different_source.get_pixel32_raw(read_point.0, read_point.1),
+                );
+            }
+        }
+    }
+
     // Apparently,
     // "numPixels:int (default = 0) — The default is 1/30 of the source area (width x height). "
     // is wrong.
@@ -1727,36 +1760,6 @@ pub fn pixel_dissolve<'gc>(
     let write_offset = (dest_region.x_min, dest_region.y_min);
     let read_offset = (source_region.x_min, source_region.y_min);
 
-    fn write_pixel(
-        write: &mut RefMut<BitmapData>,
-        different_source_than_target: &Option<Ref<BitmapData>>,
-        fill_color: i32,
-        transparency: bool,
-        base_point: (u32, u32),
-        read_offset: (u32, u32),
-        write_offset: (u32, u32),
-    ) {
-        let read_point = (read_offset.0 + base_point.0, read_offset.1 + base_point.1);
-        let write_point = (write_offset.0 + base_point.0, write_offset.1 + base_point.1);
-
-        match different_source_than_target {
-            None => {
-                write.set_pixel32_raw(
-                    write_point.0,
-                    write_point.1,
-                    Color::from(fill_color).to_premultiplied_alpha(transparency),
-                );
-            }
-            Some(different_source) => {
-                write.set_pixel32_raw(
-                    write_point.0,
-                    write_point.1,
-                    different_source.get_pixel32_raw(read_point.0, read_point.1),
-                );
-            }
-        }
-    }
-
     let different_source_than_target = if source_bitmap.ptr_eq(target) {
         None
     } else {