add blend abstraction

agb/src/display/blend.rs

@@ -0,0 +1,109 @@
+use crate::{fixnum::Num, memory_mapped::set_bits};
+
+use super::tiled::BackgroundID;
+
+#[derive(Clone, Copy, Debug)]
+pub enum Layer {
+    Top = 0,
+    Bottom = 1,
+}
+
+#[derive(Clone, Copy, Debug)]
+pub enum BlendMode {
+    Off = 0,
+    Normal = 0b01,
+    FadeToWhite = 0b10,
+    FadeToBlack = 0b11,
+}
+
+pub struct Blend {
+    targets: u16,
+    blend_weights: u16,
+    fade_weight: u16,
+}
+
+const BLEND_CONTROL: *mut u16 = 0x0400_0050 as *mut _;
+const BLEND_ALPHAS: *mut u16 = 0x0400_0052 as *mut _;
+
+const BLEND_FADES: *mut u16 = 0x0400_0054 as *mut _;
+
+impl Blend {
+    pub fn reset_targets(&mut self) -> &mut Self {
+        self.targets = 0;
+
+        self
+    }
+
+    pub fn reset_weights(&mut self) -> &mut Self {
+        self.blend_weights = 0;
+
+        self
+    }
+
+    pub fn reset_fades(&mut self) -> &mut Self {
+        self.fade_weight = 0;
+
+        self
+    }
+
+    pub fn reset(&mut self) -> &mut Self {
+        self.reset_targets().reset_fades().reset_weights()
+    }
+
+    pub fn set_background_enable(
+        &mut self,
+        layer: Layer,
+        background: BackgroundID,
+        enable: bool,
+    ) -> &mut Self {
+        let bit_to_modify = (background.0 as usize) + (layer as usize * 8);
+        self.targets = set_bits(self.targets, enable as u16, 1, bit_to_modify);
+
+        self
+    }
+
+    pub fn set_object_enable(&mut self, layer: Layer, enable: bool) -> &mut Self {
+        let bit_to_modify = 0x4 + (layer as usize * 8);
+        self.targets = set_bits(self.targets, enable as u16, 1, bit_to_modify);
+
+        self
+    }
+
+    pub fn set_backdrop_enable(&mut self, layer: Layer, enable: bool) -> &mut Self {
+        let bit_to_modify = 0x5 + (layer as usize * 8);
+        self.targets = set_bits(self.targets, enable as u16, 1, bit_to_modify);
+
+        self
+    }
+
+    pub fn set_blend_weight(&mut self, layer: Layer, value: Num<u8, 4>) -> &mut Self {
+        self.blend_weights = set_bits(
+            self.blend_weights,
+            value.to_raw() as u16,
+            5,
+            (layer as usize) * 8,
+        );
+
+        self
+    }
+
+    pub fn set_fade(&mut self, value: Num<u8, 4>) -> &mut Self {
+        self.fade_weight = value.to_raw() as u16;
+
+        self
+    }
+
+    pub fn set_blend_mode(&mut self, blend_mode: BlendMode) -> &mut Self {
+        self.targets = set_bits(self.targets, blend_mode as u16, 2, 0x6);
+
+        self
+    }
+
+    pub fn commit(&self) {
+        unsafe {
+            BLEND_CONTROL.write_volatile(self.targets);
+            BLEND_ALPHAS.write_volatile(self.blend_weights);
+            BLEND_FADES.write_volatile(self.fade_weight);
+        }
+    }
+}

agb/src/display/mod.rs

@@ -23,6 +23,7 @@ pub mod tiled;
 /// Giving out graphics mode.
 pub mod video;
 
+pub mod blend;
 pub mod window;
 
 mod font;