Simplify draw state

Closes PistonDevelopers#996

Cargo.toml

@@ -22,7 +22,6 @@ name = "graphics"
 path = "./src/lib.rs"
 
 [dependencies]
-draw_state = "0.2.0"
 interpolation = "0.1.0"
 piston-texture = "0.2.1"
 piston-viewport = "0.1.0"

src/context.rs

@@ -1,7 +1,6 @@
 //! Transformation context
 
 use draw_state::DrawState;
-use default_draw_state;
 use math::{
     abs_transform,
     identity,
@@ -33,7 +32,7 @@ impl Context {
         Context {
             view: identity(),
             transform: identity(),
-            draw_state: *default_draw_state(),
+            draw_state: Default::default(),
             viewport: None,
         }
     }
@@ -54,7 +53,7 @@ impl Context {
         Context {
             view: mat,
             transform: mat,
-            draw_state: *default_draw_state(),
+            draw_state: Default::default(),
             viewport: Some(viewport),
         }
     }
@@ -75,7 +74,7 @@ impl Context {
         Context {
             view: mat,
             transform: mat,
-            draw_state: *default_draw_state(),
+            draw_state: Default::default(),
             viewport: None,
         }
     }

src/draw_state.rs

@@ -0,0 +1,113 @@
+//! Draw state parameters.
+
+/// Draw state parameters.
+#[derive(Copy, Clone)]
+pub struct DrawState {
+    /// Blend effect.
+    pub blend: Blend,
+    /// Stencil effect.
+    pub stencil: Option<Stencil>,
+    /// Scissor rectangle.
+    /// Limits the area of rendered pixels.
+    /// Uses frame buffer coordinates.
+    pub scissor: Option<[u32; 4]>,
+}
+
+impl DrawState {
+    /// Clip draw state.
+    pub fn clip(mut self) -> DrawState {
+        self.stencil = Some(Stencil::Clip(1));
+        self
+    }
+
+    /// Inside draw state.
+    pub fn inside(mut self) -> DrawState {
+        self.stencil = Some(Stencil::Inside(1));
+        self
+    }
+
+    /// Outside draw state.
+    pub fn outside(mut self) -> DrawState {
+        self.stencil = Some(Stencil::Outside(1));
+        self
+    }
+
+    /// Blend effect.
+    pub fn blend(mut self, blend: Blend) -> DrawState {
+        self.blend = blend;
+        self
+    }
+
+    /// Stencil effect.
+    pub fn stencil(mut self, stencil: Stencil) -> DrawState {
+        self.stencil = Some(stencil);
+        self
+    }
+
+    /// Scissor rectangle.
+    pub fn scissor(mut self, scissor: [u32; 4]) -> DrawState {
+        self.scissor = Some(scissor);
+        self
+    }
+}
+
+impl Default for DrawState {
+    fn default() -> Self {
+        DrawState {
+            blend: Blend::Alpha,
+            stencil: None,
+            scissor: None,
+        }
+    }
+}
+
+#[derive(Copy, Clone)]
+/// Blend effect.
+///
+/// This effect is applied after shaders.
+/// Most hardware supports simple blending effects.
+///
+/// Simple blend effects are documented with their corresponding fixed
+/// pipeline blending equation.
+///
+/// blend_equation: `source * (blend_parameter) <op> destination * (blend_parameter)`
+pub enum Blend {
+    /// Alpha blends colors.
+    ///
+    /// color: `source * (source_alpha) + destination * (1 - source_alpha)`
+    ///
+    /// alpha: `source * (1) + destination * (1)`
+    Alpha,
+    /// Adds color components.
+    ///
+    /// color: `source * (1) + destination * (1)`
+    ///
+    /// alpha: `source * (1) + destination * (1)`
+    Add,
+    /// Multiplies the color components.
+    ///
+    /// color: `source * (destination) + destination * (0)`
+    ///
+    /// alpha: `source * (destination_alpha) + destination * (0)`
+    Multiply,
+    /// Inverts the rendered color.
+    ///
+    /// color: `source * (1) - destination * (source)`
+    ///
+    /// alpha: `source * (0) + destination * (1)`.
+    Invert,
+}
+
+#[derive(Copy, Clone)]
+/// Stencil effect.
+pub enum Stencil {
+    /// Assign stencil value to pixels that are rendered invisible.
+    /// This is used to define the area of clipping.
+    Clip(u8),
+    /// Renders pixels that has a stencil value.
+    /// This is used to render inside an area of clipping.
+    Inside(u8),
+    /// Renders pixels that does not have a stencil value.
+    /// This is used to render outside an area of clipping.
+    Outside(u8),
+}