Copy draw state code from Gfx

Closes #154

- Detect changes from previous draw state
- Added a `draw_state` module for reuse
- Added `GlGraphics::use_draw_state`
- Added `GlGraphics::clear_draw_state`

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 
 name = "piston2d-opengl_graphics"
-version = "0.14.0"
+version = "0.14.1"
 authors = [
     "bvssvni <[email protected]>",
     "Coeuvre <[email protected]>",

src/back_end.rs

@@ -206,6 +206,8 @@ pub struct GlGraphics {
     textured: Textured,
     // Keeps track of the current shader program.
     current_program: Option<GLuint>,
+    // Keeps track of the current draw state.
+    current_draw_state: Option<DrawState>,
 }
 
 impl<'a> GlGraphics {
@@ -223,6 +225,7 @@ impl<'a> GlGraphics {
             colored: Colored::new(glsl),
             textured: Textured::new(glsl),
             current_program: None,
+            current_draw_state: None,
        }
     }
 
@@ -261,6 +264,33 @@ impl<'a> GlGraphics {
         self.current_program = None
     }
 
+    /// Sets the current draw state, by detecting changes.
+    pub fn use_draw_state(&mut self, draw_state: &DrawState) {
+        match self.current_draw_state {
+            None => {
+                draw_state::bind_scissor(draw_state.scissor);
+                draw_state::bind_primitive(draw_state.primitive);
+                draw_state::bind_multi_sample(draw_state.multi_sample);
+                draw_state::bind_depth(draw_state.depth);
+                draw_state::bind_stencil(draw_state.stencil,
+                    draw_state.primitive.get_cull_face());
+                draw_state::bind_blend(draw_state.blend);
+                draw_state::bind_color_mask(draw_state.color_mask);
+            }
+            Some(ref old_state) => {
+                draw_state::bind_state(old_state, draw_state);
+            }
+        }
+        self.current_draw_state = Some(*draw_state);
+    }
+
+    /// Unsets the current draw state.
+    ///
+    /// This forces the current draw state to be set on next drawing call.
+    pub fn clear_draw_state(&mut self) {
+        self.current_draw_state = None;
+    }
+
     /// Draws graphics.
     pub fn draw<F>(&mut self, viewport: Viewport, f: F)
         where
@@ -321,21 +351,13 @@ impl Graphics for GlGraphics {
         where F: FnMut(&mut FnMut(&[f32]))
     {
         {
-            // Set shader program.
+            // Set shader program and draw state.
             let shader_program = self.colored.program;
             self.use_program(shader_program);
+            self.use_draw_state(draw_state);
         }
         let ref mut shader = self.colored;
 
-        draw_state::bind_scissor(draw_state.scissor);
-        draw_state::bind_primitive(draw_state.primitive);
-        draw_state::bind_multi_sample(draw_state.multi_sample);
-        draw_state::bind_depth(draw_state.depth);
-        draw_state::bind_stencil(draw_state.stencil,
-            draw_state.primitive.get_cull_face());
-        draw_state::bind_blend(draw_state.blend);
-        draw_state::bind_color_mask(draw_state.color_mask);
-
         unsafe {
             gl::BindVertexArray(shader.vao);
             gl::Uniform4f(shader.color, color[0], color[1], color[2], color[3]);
@@ -370,21 +392,13 @@ impl Graphics for GlGraphics {
         where F: FnMut(&mut FnMut(&[f32], &[f32]))
     {
         {
-            // Set shader program.
+            // Set shader program and draw state.
             let shader_program = self.textured.program;
             self.use_program(shader_program);
+            self.use_draw_state(draw_state);
         }
         let ref mut shader = self.textured;
 
-        draw_state::bind_scissor(draw_state.scissor);
-        draw_state::bind_primitive(draw_state.primitive);
-        draw_state::bind_multi_sample(draw_state.multi_sample);
-        draw_state::bind_depth(draw_state.depth);
-        draw_state::bind_stencil(draw_state.stencil,
-            draw_state.primitive.get_cull_face());
-        draw_state::bind_blend(draw_state.blend);
-        draw_state::bind_color_mask(draw_state.color_mask);
-
         let texture = texture.get_id();
         unsafe {
             gl::BindTexture(gl::TEXTURE_2D, texture);

src/draw_state.rs

@@ -16,7 +16,7 @@ pub fn bind_state(old_state: &DrawState, new_state: &DrawState) {
         bind_multi_sample(new_state.multi_sample);
     }
     if old_state.scissor != new_state.scissor {
-        bind_scissor(old_state.scissor);
+        bind_scissor(new_state.scissor);
     }
     if old_state.depth != new_state.depth
     || old_state.stencil != new_state.stencil