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Implement Consistent Color Generation (XEP-0392)

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This should make colors used by Delta Chat for emails similar to colors
used by XMPP clients implementing the same specification[1], such as
Conversations and Snikket.

Previously Delta Chat used only hardcoded 16 colors, so this change
should also increase the number of colors and make it easier to
distinguish different contacts.

[1] https://xmpp.org/extensions/xep-0392.html
This commit is contained in:
link2xt
2021-02-12 21:36:04 +03:00
committed by link2xt
parent 982dc53dc1
commit a2c3233c19
7 changed files with 67 additions and 35 deletions
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25
src/dc_tools.rs
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@@ -48,31 +48,6 @@ pub(crate) fn dc_truncate(buf: &str, approx_chars: usize) -> Cow<str> {
}
}
/// the colors must fulfill some criterions as:
/// - contrast to black and to white
/// - work as a text-color
/// - being noticeable on a typical map
/// - harmonize together while being different enough
/// (therefore, we cannot just use random rgb colors :)
const COLORS: [u32; 16] = [
0xe5_65_55, 0xf2_8c_48, 0x8e_85_ee, 0x76_c8_4d, 0x5b_b6_cc, 0x54_9c_dd, 0xd2_5c_99, 0xb3_78_00,
0xf2_30_30, 0x39_b2_49, 0xbb_24_3b, 0x96_40_78, 0x66_87_4f, 0x30_8a_b9, 0x12_7e_d0, 0xbe_45_0c,
];
#[allow(clippy::indexing_slicing)]
pub(crate) fn dc_str_to_color(s: impl AsRef<str>) -> u32 {
let str_lower = s.as_ref().to_lowercase();
let mut checksum = 0;
let bytes = str_lower.as_bytes();
for (i, byte) in bytes.iter().enumerate() {
checksum += (i + 1) * *byte as usize;
checksum %= 0x00ff_ffff;
}
let color_index = checksum % COLORS.len();
COLORS[color_index]
}
/* ******************************************************************************
* date/time tools
******************************************************************************/