rudimentary support for BMPs with alpha masks

"rudimentary" in the sense that the format will be allowed and parsed,
but the alpha channel is thrown away when drawing and getting pixels.

Author: samcday

src/header/mod.rs

@@ -201,6 +201,14 @@ impl ChannelMasks {
         blue: 0x0000FF,
         alpha: 0,
     };
+
+    /// Argb888 color masks.
+    pub const ARGB888: Self = Self {
+        red: 0xFF000000,
+        green: 0xFF0000,
+        blue: 0xFF00,
+        alpha: 0xFF,
+    };
 }
 
 /// Describes how the BMP file is compressed.

src/iter.rs

@@ -56,6 +56,7 @@ where
             ColorType::Rgb555 => Rgb555::from(RawU16::from_u32(color)).into(),
             ColorType::Rgb565 => Rgb565::from(RawU16::from_u32(color)).into(),
             ColorType::Rgb888 | ColorType::Xrgb8888 => Rgb888::from(RawU24::from_u32(color)).into(),
+            ColorType::Argb8888 => Rgb888::from(RawU24::from_u32(color >> 8)).into(),
         };
 
         Some(Pixel(position, color))

src/lib.rs

@@ -362,6 +362,11 @@ where
                 RawColors::<RawU32>::new(&self.raw_bmp)
                     .map(|raw| Rgb888::from(RawU24::new(raw.into_inner())).into()),
             ),
+            ColorType::Argb8888 => target.fill_contiguous(
+                &area,
+                RawColors::<RawU32>::new(&self.raw_bmp)
+                    .map(|raw| Rgb888::from(RawU24::new(raw.into_inner() >> 8)).into()),
+            ),
         }
     }
 
@@ -421,6 +426,10 @@ where
                 .raw_bmp
                 .pixel(p)
                 .map(|raw| Rgb888::from(RawU24::from_u32(raw)).into()),
+            ColorType::Argb8888 => self
+                .raw_bmp
+                .pixel(p)
+                .map(|raw| Rgb888::from(RawU24::from_u32(raw >> 8)).into()),
         }
     }
 }

src/raw_bmp.rs

@@ -157,6 +157,7 @@ pub enum ColorType {
     Rgb565,
     Rgb888,
     Xrgb8888,
+    Argb8888,
 }
 
 impl ColorType {
@@ -184,6 +185,8 @@ impl ColorType {
                 if let Some(masks) = header.channel_masks {
                     if masks == ChannelMasks::RGB888 {
                         ColorType::Xrgb8888
+                    } else if masks == ChannelMasks::ARGB888 {
+                        ColorType::Argb8888
                     } else {
                         return Err(ParseError::UnsupportedChannelMasks);
                     }