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//! Transparency representation for CAD entities
use std::fmt;
/// Represents transparency in AutoCAD
///
/// Transparency is represented as an alpha value where:
/// - 0 = fully opaque (0% transparent)
/// - 255 = fully transparent (100% transparent)
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct Transparency(u8);
impl Transparency {
/// Fully opaque (0% transparent)
pub const OPAQUE: Transparency = Transparency(0);
/// Fully transparent (100% transparent)
pub const TRANSPARENT: Transparency = Transparency(255);
/// Transparency ByLayer - uses the layer's transparency
pub const BY_LAYER: Transparency = Transparency(0);
/// Create a new transparency from an alpha value (0-255)
pub const fn new(alpha: u8) -> Self {
Transparency(alpha)
}
/// Create transparency from a percentage (0.0 = opaque, 1.0 = transparent)
pub fn from_percent(percent: f64) -> Self {
let alpha = (percent.clamp(0.0, 1.0) * 255.0) as u8;
Transparency(alpha)
}
/// Create transparency from a packed alpha value (32-bit format).
///
/// Works for both DWG and DXF formats:
/// - `0` → ByLayer
/// - Type byte `1` → ByBlock (treated as opaque)
/// - Type byte `2` (DXF code 440) → explicit value in low byte
/// - Type byte `3` (DWG ENC) → explicit value in low byte
///
/// The on-disk low byte is an **alpha/opacity** value (`255` = fully
/// opaque, `0` = fully transparent), which is the inverse of this type's
/// internal representation (`0` = opaque, `255` = fully transparent), so
/// the explicit value is inverted here.
pub fn from_alpha_value(value: u32) -> Self {
let type_byte = (value >> 24) as u8;
match type_byte {
0 => Transparency::BY_LAYER,
1 => Transparency::OPAQUE, // BYBLOCK = opaque for now
2 | 3 => Transparency(255 - (value & 0xFF) as u8),
_ => Transparency::OPAQUE,
}
}
/// Get the raw alpha value (0-255)
pub const fn alpha(&self) -> u8 {
self.0
}
/// Get transparency as a percentage (0.0 = opaque, 1.0 = transparent)
pub fn as_percent(&self) -> f64 {
self.0 as f64 / 255.0
}
/// Check if fully opaque
pub const fn is_opaque(&self) -> bool {
self.0 == 0
}
/// Check if fully transparent
pub const fn is_transparent(&self) -> bool {
self.0 == 255
}
/// Common transparency values
pub const T_10: Transparency = Transparency(26); // 10% transparent
pub const T_20: Transparency = Transparency(51); // 20% transparent
pub const T_30: Transparency = Transparency(77); // 30% transparent
pub const T_40: Transparency = Transparency(102); // 40% transparent
pub const T_50: Transparency = Transparency(128); // 50% transparent
pub const T_60: Transparency = Transparency(153); // 60% transparent
pub const T_70: Transparency = Transparency(179); // 70% transparent
pub const T_80: Transparency = Transparency(204); // 80% transparent
pub const T_90: Transparency = Transparency(230); // 90% transparent
/// Convert to DWG alpha value (32-bit format, type byte 3).
///
/// The low byte written is the on-disk **alpha/opacity** (`255` = opaque),
/// the inverse of the internal transparency-amount representation.
pub fn to_alpha_value(&self) -> i32 {
if self.0 == 0 {
0
} else {
// Type 3 = explicit value (DWG); low byte = opacity = 255 - transparency
((3u32 << 24) | (255 - self.0) as u32) as i32
}
}
/// Convert to DXF code 440 value (32-bit format, type byte 2).
///
/// The low byte written is the on-disk **alpha/opacity** (`255` = opaque),
/// the inverse of the internal transparency-amount representation.
pub fn to_dxf_value(&self) -> i32 {
if self.0 == 0 {
0
} else {
// Type 2 = explicit value (DXF); low byte = opacity = 255 - transparency
((2u32 << 24) | (255 - self.0) as u32) as i32
}
}
}
impl Default for Transparency {
fn default() -> Self {
Transparency::OPAQUE
}
}
impl From<u8> for Transparency {
fn from(alpha: u8) -> Self {
Transparency(alpha)
}
}
impl From<Transparency> for u8 {
fn from(transparency: Transparency) -> Self {
transparency.0
}
}
impl fmt::Display for Transparency {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{:.1}%", self.as_percent() * 100.0)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_transparency_creation() {
let t = Transparency::new(128);
assert_eq!(t.alpha(), 128);
}
#[test]
fn test_transparency_from_percent() {
let t = Transparency::from_percent(0.5);
// 0.5 * 255.0 = 127.5, which rounds down to 127
assert_eq!(t.alpha(), 127);
let t = Transparency::from_percent(0.0);
assert_eq!(t.alpha(), 0);
let t = Transparency::from_percent(1.0);
assert_eq!(t.alpha(), 255);
}
#[test]
fn test_transparency_as_percent() {
assert_eq!(Transparency::OPAQUE.as_percent(), 0.0);
assert_eq!(Transparency::TRANSPARENT.as_percent(), 1.0);
assert!((Transparency::T_50.as_percent() - 0.5).abs() < 0.01);
}
#[test]
fn test_transparency_checks() {
assert!(Transparency::OPAQUE.is_opaque());
assert!(!Transparency::OPAQUE.is_transparent());
assert!(Transparency::TRANSPARENT.is_transparent());
assert!(!Transparency::TRANSPARENT.is_opaque());
}
#[test]
fn test_transparency_display() {
assert_eq!(Transparency::OPAQUE.to_string(), "0.0%");
assert_eq!(Transparency::TRANSPARENT.to_string(), "100.0%");
}
#[test]
fn test_transparency_conversion() {
let alpha: u8 = 100;
let t: Transparency = alpha.into();
let back: u8 = t.into();
assert_eq!(alpha, back);
}
#[test]
fn test_default_transparency() {
assert_eq!(Transparency::default(), Transparency::OPAQUE);
}
#[test]
fn test_packed_value_is_opacity_inverted() {
// On-disk low byte is opacity (255 = opaque), inverse of the internal
// transparency-amount representation.
// 0x020000FF: fully opaque.
assert_eq!(Transparency::from_alpha_value(0x0200_00FF), Transparency::OPAQUE);
// 0x02000026 (byte 38 opacity) → 85% transparent (internal byte 217).
let t = Transparency::from_alpha_value(0x0200_0026);
assert_eq!(t.alpha(), 217);
assert!((t.as_percent() - 0.85).abs() < 0.01);
// 0x02000000 (opacity 0) → fully transparent.
assert_eq!(Transparency::from_alpha_value(0x0200_0000), Transparency::TRANSPARENT);
}
#[test]
fn test_packed_value_roundtrip() {
// An 85%-transparent value (internal 217) writes opacity byte 38 to
// both DWG (type 3) and DXF (type 2), and reads back unchanged.
let t = Transparency::new(217);
assert_eq!(t.to_dxf_value() as u32, 0x0200_0026);
assert_eq!(t.to_alpha_value() as u32, 0x0300_0026);
assert_eq!(Transparency::from_alpha_value(t.to_dxf_value() as u32), t);
assert_eq!(Transparency::from_alpha_value(t.to_alpha_value() as u32), t);
}
}