engine/map/src/tile.rs

use engine::prelude::cgmath::{Vector2, Vector3};

use super::{mapdata::Coordinate, surface::Surface};

#[derive(Clone, Copy, Debug)]
pub enum SlopeDirection {
    LeftToRight,
    RightToLeft,
    TopToBottom,
    BottomToTop,
    DiagonalBottomLeftToTopRight,
    DiagonalTopLeftToBottomRight,
    DiagonalTopRightToBottomLeft,
    DiagonalBottomRightToTopLeft,
}

impl SlopeDirection {
    pub fn from_direction(direction: Vector2<f32>) -> SlopeDirection {
        if direction.x < 0.0 {
            if direction.y < 0.0 {
                if Self::almost_eq(direction.x, direction.y) {
                    SlopeDirection::DiagonalTopRightToBottomLeft
                } else if direction.x < direction.y {
                    SlopeDirection::RightToLeft
                } else {
                    SlopeDirection::TopToBottom
                }
            } else if Self::almost_eq(direction.x.abs(), direction.y) {
                SlopeDirection::DiagonalBottomRightToTopLeft
            } else if direction.x.abs() < direction.y {
                SlopeDirection::BottomToTop
            } else {
                SlopeDirection::RightToLeft
            }
        } else if direction.y < 0.0 {
            if Self::almost_eq(direction.x, direction.y.abs()) {
                SlopeDirection::DiagonalTopLeftToBottomRight
            } else if direction.x < direction.y.abs() {
                SlopeDirection::TopToBottom
            } else {
                SlopeDirection::LeftToRight
            }
        } else if Self::almost_eq(direction.x, direction.y) {
            SlopeDirection::DiagonalBottomLeftToTopRight
        } else if direction.x < direction.y {
            SlopeDirection::BottomToTop
        } else {
            SlopeDirection::LeftToRight
        }
    }

    #[inline]
    fn almost_eq(f1: f32, f2: f32) -> bool {
        let epsilon = 0.001;

        (f1 + epsilon > f2) && (f1 - epsilon < f2)
    }
}

#[derive(Debug)]
pub struct Tile {
    pub left_bottom: Vector3<f32>,
    pub right_bottom: Vector3<f32>,
    pub left_top: Vector3<f32>,
    pub right_top: Vector3<f32>,
}

impl Tile {
    pub fn new(base_coord: Coordinate, surface: &Surface) -> Tile {
        Tile {
            left_bottom: surface.point(base_coord.x, base_coord.y),
            right_bottom: surface.point(base_coord.x + 1, base_coord.y),
            left_top: surface.point(base_coord.x, base_coord.y + 1),
            right_top: surface.point(base_coord.x + 1, base_coord.y + 1),
        }
    }

    /// checks for the slope in given direction with given threshold
    ///
    /// returns `true` when slope is below threshold, `false` otherwise
    pub fn check_slope(
        &self,
        threshold: f32,
        direction: SlopeDirection,
        increase_only: bool,
    ) -> bool {
        match direction {
            SlopeDirection::LeftToRight => {
                let bottom_difference = self.left_bottom.z - self.right_bottom.z;

                // check bottom slope against threshold
                if !Self::check_directed_slope(bottom_difference, threshold, increase_only) {
                    return false;
                }

                let top_difference = self.left_top.z - self.right_top.z;

                //check top slope against threshold
                if !Self::check_directed_slope(top_difference, threshold, increase_only) {
                    return false;
                }
            }
            SlopeDirection::RightToLeft => {
                let bottom_difference = self.right_bottom.z - self.left_bottom.z;

                if !Self::check_directed_slope(bottom_difference, threshold, increase_only) {
                    return false;
                }

                let top_difference = self.right_top.z - self.left_top.z;

                if !Self::check_directed_slope(top_difference, threshold, increase_only) {
                    return false;
                }
            }
            SlopeDirection::BottomToTop => {
                let left_difference = self.left_bottom.z - self.left_top.z;

                if !Self::check_directed_slope(left_difference, threshold, increase_only) {
                    return false;
                }

                let right_difference = self.right_bottom.z - self.right_top.z;

                if !Self::check_directed_slope(right_difference, threshold, increase_only) {
                    return false;
                }
            }
            SlopeDirection::TopToBottom => {
                let left_difference = self.left_top.z - self.left_bottom.z;

                if !Self::check_directed_slope(left_difference, threshold, increase_only) {
                    return false;
                }

                let right_difference = self.right_top.z - self.right_bottom.z;

                if !Self::check_directed_slope(right_difference, threshold, increase_only) {
                    return false;
                }
            }
            SlopeDirection::DiagonalBottomLeftToTopRight => {
                let diagonal_difference = self.left_bottom.z - self.right_top.z;

                if !Self::check_directed_slope(diagonal_difference, threshold, increase_only) {
                    return false;
                }
            }
            SlopeDirection::DiagonalBottomRightToTopLeft => {
                let diagonal_difference = self.right_bottom.z - self.left_top.z;

                if !Self::check_directed_slope(diagonal_difference, threshold, increase_only) {
                    return false;
                }
            }
            SlopeDirection::DiagonalTopLeftToBottomRight => {
                let diagonal_difference = self.left_top.z - self.right_bottom.z;

                if !Self::check_directed_slope(diagonal_difference, threshold, increase_only) {
                    return false;
                }
            }
            SlopeDirection::DiagonalTopRightToBottomLeft => {
                let diagonal_difference = self.right_top.z - self.left_bottom.z;

                if !Self::check_directed_slope(diagonal_difference, threshold, increase_only) {
                    return false;
                }
            }
        }

        true
    }

    #[inline]
    fn check_directed_slope(difference: f32, threshold: f32, increase_only: bool) -> bool {
        // check slope against threshold
        if difference.abs() > threshold {
            // if increase only, check for increase
            if increase_only {
                if difference < 0.0 {
                    return false;
                }
            } else {
                return false;
            }
        }

        true
    }
}