Move some decoder fields into a new Image struct

src/decoder/image.rs

@@ -0,0 +1,96 @@
+use super::ChunkType;
+use super::ifd::Directory;
+use crate::tags::{
+    CompressionMethod, PhotometricInterpretation, Predictor, SampleFormat,
+};
+
+#[derive(Debug)]
+pub(crate) struct StripDecodeState {
+    pub rows_per_strip: u32,
+}
+
+#[derive(Debug)]
+/// Computed values useful for tile decoding
+pub(crate) struct TileAttributes {
+    pub image_width: usize,
+    pub image_height: usize,
+    pub samples_per_pixel: usize,
+
+    pub tile_width: usize,
+    pub tile_length: usize,
+}
+
+impl TileAttributes {
+    pub fn tiles_across(&self) -> usize {
+        (self.image_width + self.tile_width - 1) / self.tile_width
+    }
+    pub fn tiles_down(&self) -> usize {
+        (self.image_height + self.tile_length - 1) / self.tile_length
+    }
+    fn padding_right(&self) -> usize {
+        self.tile_width - self.image_width % self.tile_width
+    }
+    fn padding_down(&self) -> usize {
+        self.tile_length - self.image_height % self.tile_length
+    }
+    pub fn row_samples(&self) -> usize {
+        self.tile_width * self.samples_per_pixel
+    }
+    pub fn tile_samples(&self) -> usize {
+        self.tile_length * self.tile_width * self.samples_per_pixel
+    }
+    fn tile_strip_samples(&self) -> usize {
+        (self.tile_samples() * self.tiles_across())
+            - (self.padding_right() * self.tile_length * self.samples_per_pixel)
+    }
+
+    /// Returns the tile offset in the result buffer, counted in samples
+    pub fn get_offset(&self, tile: usize) -> usize {
+        let row = tile / self.tiles_across();
+        let column = tile % self.tiles_across();
+
+        (row * self.tile_strip_samples()) + (column * self.row_samples())
+    }
+
+    pub fn get_padding(&self, tile: usize) -> (usize, usize) {
+        let row = tile / self.tiles_across();
+        let column = tile % self.tiles_across();
+
+        let padding_right = if column == self.tiles_across() - 1 {
+            self.padding_right()
+        } else {
+            0
+        };
+
+        let padding_down = if row == self.tiles_down() - 1 {
+            self.padding_down()
+        } else {
+            0
+        };
+
+        (padding_right, padding_down)
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct Image {
+    pub ifd: Option<Directory>,
+    pub width: u32,
+    pub height: u32,
+    pub bits_per_sample: Vec<u8>,
+    pub samples: u8,
+    pub sample_format: Vec<SampleFormat>,
+    pub photometric_interpretation: PhotometricInterpretation,
+    pub compression_method: CompressionMethod,
+    pub predictor: Predictor,
+    pub jpeg_tables: Option<Vec<u8>>,
+    pub chunk_type: ChunkType,
+    pub strip_decoder: Option<StripDecodeState>,
+    pub tile_attributes: Option<TileAttributes>,
+    pub chunk_offsets: Vec<u64>,
+    pub chunk_bytes: Vec<u64>,
+}
+
+impl Image {
+
+}