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Add Pixmap::take_demultiplied to get raw, demultiplied pixel data #152

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Merged
LaurenzV merged 1 commit into from
Aug 15, 2025
Merged

Add Pixmap::take_demultiplied to get raw, demultiplied pixel data #152

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30 changes: 18 additions & 12 deletions src/pixmap.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -260,6 +260,22 @@ impl Pixmap {
self.data
}

/// Consumes the pixmap and returns the internal data as demultiplied RGBA bytes.
///
/// Byteorder: RGBA
pub fn take_demultiplied(mut self) -> Vec<u8> {
// Demultiply alpha.
//
// RasterPipeline is 15% faster here, but produces slightly different results
// due to rounding. So we stick with this method for now.
for pixel in self.pixels_mut() {
let c = pixel.demultiply();
*pixel =
PremultipliedColorU8::from_rgba_unchecked(c.red(), c.green(), c.blue(), c.alpha());
}
self.data
}

/// Returns a copy of the pixmap that intersects the `rect`.
///
/// Returns `None` when `Pixmap`'s rect doesn't contain `rect`.
Expand Down Expand Up @@ -394,25 +410,15 @@ impl<'a> PixmapRef<'a> {
// Sadly, we have to copy the pixmap here, because of demultiplication.
// Not sure how to avoid this.
// TODO: remove allocation
let mut tmp_pixmap = self.to_owned();

// Demultiply alpha.
//
// RasterPipeline is 15% faster here, but produces slightly different results
// due to rounding. So we stick with this method for now.
for pixel in tmp_pixmap.pixels_mut() {
let c = pixel.demultiply();
*pixel =
PremultipliedColorU8::from_rgba_unchecked(c.red(), c.green(), c.blue(), c.alpha());
}
let demultiplied_data = self.to_owned().take_demultiplied();

let mut data = Vec::new();
{
let mut encoder = png::Encoder::new(&mut data, self.width(), self.height());
encoder.set_color(png::ColorType::Rgba);
encoder.set_depth(png::BitDepth::Eight);
let mut writer = encoder.write_header()?;
writer.write_image_data(&tmp_pixmap.data)?;
writer.write_image_data(&demultiplied_data)?;
}

Ok(data)
Expand Down