Simplified iterator
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Kornel Lesiński
parent
e05c2f6268
commit
ba8c0b4d2f
2 changed files with 76 additions and 103 deletions
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@ -224,12 +224,7 @@ impl PngData {
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/// Return an iterator over the scanlines of the image
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/// Return an iterator over the scanlines of the image
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#[inline]
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#[inline]
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pub fn scan_lines(&self) -> ScanLines {
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pub fn scan_lines(&self) -> ScanLines {
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ScanLines {
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ScanLines::new(self)
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png: self,
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start: 0,
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end: 0,
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pass: None,
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}
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}
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}
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/// Reverse all filters applied on the image, returning an unfiltered IDAT bytestream
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/// Reverse all filters applied on the image, returning an unfiltered IDAT bytestream
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@ -4,125 +4,103 @@ use super::PngData;
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/// An iterator over the scan lines of a PNG image
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/// An iterator over the scan lines of a PNG image
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pub struct ScanLines<'a> {
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pub struct ScanLines<'a> {
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/// A reference to the PNG image being iterated upon
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/// A reference to the PNG image being iterated upon
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pub png: &'a PngData,
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start: usize,
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pub start: usize,
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pub end: usize,
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/// Current pass number, and 0-indexed row within the pass
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/// Current pass number, and 0-indexed row within the pass
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pub pass: Option<(u8, u32)>,
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pass: Option<(u8, u32)>,
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bits_per_pixel: u8,
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width: u32,
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height: u32,
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raw_data: &'a [u8],
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}
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impl<'a> ScanLines<'a> {
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pub fn new(png: &'a PngData) -> Self {
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Self {
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bits_per_pixel: png.ihdr_data.bit_depth.as_u8() * png.channels_per_pixel(),
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width: png.ihdr_data.width,
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height: png.ihdr_data.height,
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raw_data: &png.raw_data,
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start: 0,
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pass: if png.ihdr_data.interlaced == 1 {Some((1, 0))} else {None},
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}
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}
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}
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}
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impl<'a> Iterator for ScanLines<'a> {
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impl<'a> Iterator for ScanLines<'a> {
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type Item = ScanLine<'a>;
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type Item = ScanLine<'a>;
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fn next(&mut self) -> Option<Self::Item> {
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fn next(&mut self) -> Option<Self::Item> {
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if self.end == self.png.raw_data.len() {
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if self.start >= self.raw_data.len() {
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None
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None
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} else if self.png.ihdr_data.interlaced == 1 {
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} else if let Some(ref mut pass) = self.pass {
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// Scanlines for interlaced PNG files
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// Scanlines for interlaced PNG files
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if self.pass.is_none() {
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self.pass = Some((1, 0));
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}
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// Handle edge cases for images smaller than 5 pixels in either direction
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// Handle edge cases for images smaller than 5 pixels in either direction
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if self.png.ihdr_data.width < 5 && self.pass.unwrap().0 == 2 {
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if self.width < 5 && pass.0 == 2 {
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if let Some(pass) = self.pass.as_mut() {
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pass.0 = 3;
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pass.0 = 3;
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pass.1 = 4;
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pass.1 = 4;
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}
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}
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}
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// Intentionally keep these separate so that they can be applied one after another
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// Intentionally keep these separate so that they can be applied one after another
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if self.png.ihdr_data.height < 5 && self.pass.unwrap().0 == 3 {
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if self.height < 5 && pass.0 == 3 {
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if let Some(pass) = self.pass.as_mut() {
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pass.0 = 4;
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pass.0 = 4;
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pass.1 = 0;
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pass.1 = 0;
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}
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}
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}
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let bits_per_pixel = u32::from(self.png.ihdr_data.bit_depth.as_u8())
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let (pixels_factor, y_steps) = match pass {
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* u32::from(self.png.channels_per_pixel());
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(1, _) | (2, _) => (8, 8),
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let y_steps;
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(3, _) => (4, 8),
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let pixels_factor;
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(4, _) => (4, 4),
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match self.pass {
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(5, _) => (2, 4),
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Some((1, _)) | Some((2, _)) => {
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(6, _) => (2, 2),
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pixels_factor = 8;
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(7, _) => (1, 2),
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y_steps = 8;
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}
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Some((3, _)) => {
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pixels_factor = 4;
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y_steps = 8;
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}
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Some((4, _)) => {
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pixels_factor = 4;
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y_steps = 4;
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}
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Some((5, _)) => {
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pixels_factor = 2;
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y_steps = 4;
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}
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Some((6, _)) => {
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pixels_factor = 2;
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y_steps = 2;
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}
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Some((7, _)) => {
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pixels_factor = 1;
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y_steps = 2;
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}
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_ => unreachable!(),
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_ => unreachable!(),
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}
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let mut pixels_per_line = self.png.ihdr_data.width / pixels_factor as u32;
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// Determine whether to add pixels if there is a final, incomplete 8x8 block
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let gap = self.png.ihdr_data.width % pixels_factor;
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if gap > 0 {
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match self.pass.unwrap().0 {
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1 | 3 | 5 => {
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pixels_per_line += 1;
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}
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2 if gap >= 5 => {
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pixels_per_line += 1;
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}
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4 if gap >= 3 => {
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pixels_per_line += 1;
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}
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6 if gap >= 2 => {
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pixels_per_line += 1;
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}
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_ => (),
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};
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}
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let current_pass = if let Some(pass) = self.pass {
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Some(pass.0)
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} else {
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None
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};
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};
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let bytes_per_line = ((pixels_per_line * bits_per_pixel + 7) / 8) as usize;
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let mut pixels_per_line = self.width / pixels_factor as u32;
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self.start = self.end;
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// Determine whether to add pixels if there is a final, incomplete 8x8 block
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self.end = self.start + bytes_per_line + 1;
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let gap = self.width % pixels_factor;
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if let Some(pass) = self.pass.as_mut() {
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match pass.0 {
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if pass.1 + y_steps >= self.png.ihdr_data.height {
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1 | 3 | 5 if gap > 0 => {
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pass.0 += 1;
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pixels_per_line += 1;
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pass.1 = match pass.0 {
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3 => 4,
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5 => 2,
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7 => 1,
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_ => 0,
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};
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} else {
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pass.1 += y_steps;
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}
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}
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2 if gap >= 5 => {
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pixels_per_line += 1;
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}
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4 if gap >= 3 => {
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pixels_per_line += 1;
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}
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6 if gap >= 2 => {
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pixels_per_line += 1;
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}
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_ => (),
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};
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let current_pass = Some(pass.0);
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let bytes_per_line = ((pixels_per_line * self.bits_per_pixel as u32 + 7) / 8) as usize;
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if pass.1 + y_steps >= self.height {
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pass.0 += 1;
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pass.1 = match pass.0 {
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3 => 4,
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5 => 2,
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7 => 1,
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_ => 0,
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};
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} else {
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pass.1 += y_steps;
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}
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}
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let start = self.start;
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let len = bytes_per_line + 1;
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self.start += len;
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Some(ScanLine {
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Some(ScanLine {
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filter: self.png.raw_data[self.start],
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filter: self.raw_data[start],
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data: &self.png.raw_data[(self.start + 1)..self.end],
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data: &self.raw_data[(start + 1)..(start + len)],
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pass: current_pass,
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pass: current_pass,
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})
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})
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} else {
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} else {
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// Standard, non-interlaced PNG scanlines
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// Standard, non-interlaced PNG scanlines
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let bits_per_line = self.png.ihdr_data.width as usize
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let bits_per_line = self.width * self.bits_per_pixel as u32;
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* self.png.ihdr_data.bit_depth.as_u8() as usize
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let bytes_per_line = ((bits_per_line + 7) / 8) as usize;
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* self.png.channels_per_pixel() as usize;
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let start = self.start;
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let bytes_per_line = (bits_per_line + 7) / 8 as usize;
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let len = bytes_per_line + 1;
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self.start = self.end;
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self.start += len;
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self.end = self.start + bytes_per_line + 1;
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Some(ScanLine {
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Some(ScanLine {
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filter: self.png.raw_data[self.start],
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filter: self.raw_data[start],
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data: &self.png.raw_data[(self.start + 1)..self.end],
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data: &self.raw_data[(start + 1)..(start + len)],
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pass: None,
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pass: None,
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})
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})
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}
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}
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