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use crate::math::*;
use crate::core::*;
use crate::camera::*;
use crate::effect::*;

///
/// An effect that simulates fog, ie. the entire screen gets hazy white when objects are far away.
///
pub struct FogEffect {
    pub color: Vec3,
    pub density: f32,
    pub animation: f32,
    image_effect: ImageEffect
}

impl FogEffect {

    pub fn new(gl: &Context) -> Result<FogEffect, Error>
    {
        Ok(FogEffect {color: vec3(0.8, 0.8, 0.8), density: 0.2, animation: 0.1, image_effect: ImageEffect::new(gl, include_str!("shaders/fog.frag"))?})
    }

    pub fn apply(&self, viewport: Viewport, camera: &Camera, depth_texture: &dyn Texture, time: f32) -> Result<(), Error>
    {
        let render_states = RenderStates {cull: CullType::Back, write_mask: WriteMask::COLOR,
            blend: Some(BlendParameters::TRANSPARENCY),
            ..Default::default()};

        self.image_effect.program().use_texture(depth_texture, "depthMap")?;
        self.image_effect.program().use_uniform_mat4("viewProjectionInverse", &(camera.projection() * camera.view()).invert().unwrap())?;
        self.image_effect.program().use_uniform_vec3("fogColor", &self.color)?;
        self.image_effect.program().use_uniform_float("fogDensity", &self.density)?;
        self.image_effect.program().use_uniform_float("animation", &self.animation)?;
        self.image_effect.program().use_uniform_float("time", &(0.001 * time))?;
        self.image_effect.program().use_uniform_vec3("eyePosition", camera.position())?;

        self.image_effect.apply(render_states, viewport)?;
        Ok(())
    }

}