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use crate::core::*;
use crate::math::*;

///
/// A customizable 2D effect.
/// Can for example be used for adding an effect on top of the rendered 3D scene, like [fog](crate::FogEffect).
///
pub struct ImageEffect {
    program: Program,
    positions: VertexBuffer,
    uvs: VertexBuffer,
}

impl ImageEffect {
    pub fn new(context: &Context, fragment_shader: &str) -> Result<Self, Error> {
        let program = Program::from_source(
            &context,
            "in vec3 position;
                                                    in vec2 uv_coordinate;
                                                    out vec2 uv;
                                                    void main()
                                                    {
                                                        uv = uv_coordinate;
                                                        gl_Position = vec4(position, 1.0);
                                                    }",
            fragment_shader,
        )?;

        let positions = vec![-3.0, -1.0, 0.0, 3.0, -1.0, 0.0, 0.0, 2.0, 0.0];
        let uvs = vec![-1.0, 0.0, 2.0, 0.0, 0.5, 1.5];
        let positions = VertexBuffer::new_with_static_f32(&context, &positions).unwrap();
        let uvs = VertexBuffer::new_with_static_f32(&context, &uvs).unwrap();

        Ok(Self {
            program,
            positions,
            uvs,
        })
    }

    pub fn apply(&self, render_states: RenderStates, viewport: Viewport) -> Result<(), Error> {
        self.program
            .use_attribute_vec3(&self.positions, "position")?;
        self.program
            .use_attribute_vec2(&self.uvs, "uv_coordinate")?;
        self.program
            .draw_arrays(render_states, CullType::Back, viewport, 3);
        Ok(())
    }
}

impl std::ops::Deref for ImageEffect {
    type Target = Program;

    fn deref(&self) -> &Self::Target {
        &self.program
    }
}