37 lines
1.1 KiB
Rust
37 lines
1.1 KiB
Rust
use png::PngData;
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pub fn reduce_alpha_channel(png: &mut PngData, channels: usize) -> Option<Vec<u8>> {
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let byte_depth: u8 = png.ihdr_data.bit_depth.as_u8() >> 3;
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let bpp: usize = channels * byte_depth as usize;
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let colored_bytes = bpp - byte_depth as usize;
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for line in png.scan_lines() {
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for (i, &byte) in line.data.iter().enumerate() {
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if i % bpp >= colored_bytes {
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if byte != 255 {
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return None;
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}
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}
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}
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}
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let mut reduced = Vec::with_capacity(png.raw_data.len());
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for line in png.scan_lines() {
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reduced.push(line.filter);
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for (i, &byte) in line.data.iter().enumerate() {
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if i % bpp >= colored_bytes {
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continue;
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} else {
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reduced.push(byte);
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}
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}
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}
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// sBIT contains information about alpha channel's original depth,
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// and alpha has just been removed
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if let Some(sbit_header) = png.aux_headers.get_mut(&"sBIT".to_string()) {
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assert_eq!(sbit_header.len(), channels);
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sbit_header.pop();
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}
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Some(reduced)
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}
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