Add ImageAlphaType

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>

Author: sagudev

src/image.rs

@@ -29,6 +29,17 @@ impl ImageFormat {
     }
 }
 
+/// Handling of alpha channel
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[repr(u8)]
+pub enum ImageAlphaType {
+    /// Image has separate alpha channel (also called straight/unpremultiplied alpha).
+    Alpha = 1,
+    /// Image has colors with premultiplied alpha
+    AlphaPremultiplied = 0,
+}
+
 /// Defines the desired quality for sampling an image.
 #[derive(Copy, Clone, PartialEq, Eq, Default, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
@@ -58,6 +69,8 @@ pub struct ImageData {
     pub data: Blob<u8>,
     /// Pixel format of the image.
     pub format: ImageFormat,
+    /// Encoding of alpha in the image pixels
+    pub alpha_type: ImageAlphaType,
     /// Width of the image.
     pub width: u32,
     /// Height of the image.

src/impl_bytemuck.rs

@@ -3,7 +3,7 @@
 
 #![allow(unsafe_code, reason = "unsafe is required for bytemuck unsafe impls")]
 
-use crate::{Compose, Extend, Fill, ImageFormat, ImageQuality, Mix};
+use crate::{Compose, Extend, Fill, ImageAlphaType, ImageFormat, ImageQuality, Mix};
 
 // Safety: The enum is `repr(u8)` and has only fieldless variants.
 unsafe impl bytemuck::NoUninit for Compose {}
@@ -109,6 +109,31 @@ unsafe impl bytemuck::Contiguous for ImageFormat {
     const MAX_VALUE: u8 = Self::Rgba8 as u8;
 }
 
+// Safety: The enum is `repr(u8)` and has only fieldless variants.
+unsafe impl bytemuck::NoUninit for ImageAlphaType {}
+
+// Safety: The enum is `repr(u8)` and `0` is a valid value.
+unsafe impl bytemuck::Zeroable for ImageAlphaType {}
+
+// Safety: The enum is `repr(u8)`.
+unsafe impl bytemuck::checked::CheckedBitPattern for ImageAlphaType {
+    type Bits = u8;
+
+    fn is_valid_bit_pattern(bits: &u8) -> bool {
+        use bytemuck::Contiguous;
+        // Don't need to compare against MIN_VALUE as this is u8 and 0 is the MIN_VALUE.
+        *bits <= Self::MAX_VALUE
+    }
+}
+
+// Safety: The enum is `repr(u8)`. All values are `u8` and fall within
+// the min and max values.
+unsafe impl bytemuck::Contiguous for ImageAlphaType {
+    type Int = u8;
+    const MIN_VALUE: u8 = Self::Alpha as u8;
+    const MAX_VALUE: u8 = Self::AlphaPremultiplied as u8;
+}
+
 // Safety: The enum is `repr(u8)` and has only fieldless variants.
 unsafe impl bytemuck::NoUninit for ImageQuality {}
 
@@ -151,7 +176,7 @@ unsafe impl bytemuck::checked::CheckedBitPattern for Mix {
 
 #[cfg(test)]
 mod tests {
-    use crate::{Compose, Extend, Fill, ImageFormat, ImageQuality, Mix};
+    use crate::{Compose, Extend, Fill, ImageAlphaType, ImageFormat, ImageQuality, Mix};
     use bytemuck::{checked::try_from_bytes, Contiguous, Zeroable};
     use core::ptr;
 

src/lib.rs

@@ -52,7 +52,8 @@ pub use gradient::{
     RadialGradientPosition, SweepGradientPosition,
 };
 pub use image::{
-    ImageBrush, ImageBrushRef, ImageData, ImageFormat, ImageQuality, ImageRenderParams,
+    ImageAlphaType, ImageBrush, ImageBrushRef, ImageData, ImageFormat, ImageQuality,
+    ImageRenderParams,
 };
 pub use style::{Fill, Style, StyleRef};