From 58706af0c514d5eb9d0ffb9f478e16ba3acd575a Mon Sep 17 00:00:00 2001
From: Ian Tayler <iangtayler@gmail.com>
Date: Wed, 18 Nov 2020 14:51:23 -0300
Subject: [PATCH] Implement reduction of player collision boxes with ball.

When the ball is going fast and the player is not a goalie.
---
 assets/sprites/player.ron       |  3 ++-
 src/components/collision_box.rs |  2 +-
 src/components/player.rs        | 23 ++++++++++++++++++++++-
 src/config.rs                   |  5 +++++
 src/systems/collision.rs        | 16 ++++++++++++----
 5 files changed, 42 insertions(+), 7 deletions(-)

diff --git a/assets/sprites/player.ron b/assets/sprites/player.ron
index 036b1a3..f1a08ff 100644
--- a/assets/sprites/player.ron
+++ b/assets/sprites/player.ron
@@ -128,7 +128,8 @@ Prefab(
                         push_strength: 96.0,
                         side: UpperSide,
                     ),
-                    robot: Robot(logic_module: EngineRunner("basic")),
+                    human: Human,
+                    // robot: Robot(logic_module: EngineRunner("basic")),
                 ),
             ),
         ),
diff --git a/src/components/collision_box.rs b/src/components/collision_box.rs
index b0f481e..a80a961 100644
--- a/src/components/collision_box.rs
+++ b/src/components/collision_box.rs
@@ -8,7 +8,7 @@ use amethyst::{
 };
 use serde::{Deserialize, Serialize};
 
-#[derive(Debug, Deserialize, Clone, Serialize, PrefabData)]
+#[derive(Debug, Deserialize, Copy, Clone, Serialize, PrefabData)]
 #[prefab(Component)]
 pub struct CollisionBox {
     /// Distance from the center to the upper left.
diff --git a/src/components/player.rs b/src/components/player.rs
index 5c0d0d6..d8ee551 100644
--- a/src/components/player.rs
+++ b/src/components/player.rs
@@ -1,4 +1,4 @@
-use crate::{config, utils};
+use crate::{components::CollisionBox, config, utils};
 use amethyst::{
     assets::PrefabData,
     derive::PrefabData,
@@ -72,3 +72,24 @@ impl PlayerType {
 impl Component for PlayerType {
     type Storage = DenseVecStorage<Self>;
 }
+
+/// Makes balls that go fast collide less with players.
+pub fn reduce_collision(
+    player_collision: &CollisionBox,
+    player_type: &PlayerType,
+    ball_speed: f32,
+) -> CollisionBox {
+    match player_type {
+        PlayerType::Goalie => *player_collision,
+        _ => {
+            let max_speed = config::BALL_SPEED_FOR_MINIMUM_COLLISION;
+            let min_factor = config::BALL_MINIMUM_COLLISION_FACTOR;
+            let reduce_factor = ball_speed.min(max_speed) * (1.0 - min_factor) / max_speed;
+            let keep_factor = 1.0 - reduce_factor;
+            CollisionBox {
+                upper_left_distance: player_collision.upper_left_distance * keep_factor,
+                lower_right_distance: player_collision.lower_right_distance * keep_factor,
+            }
+        }
+    }
+}
diff --git a/src/config.rs b/src/config.rs
index 8976e47..cbb5717 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1,6 +1,11 @@
 // TODO: move this to configuration files?
+// Screen constants
 pub const SCREEN_WIDTH: f32 = 256.0;
 pub const SCREEN_HEIGHT: f32 = 256.0;
+// Some ~physics constants
+pub const BALL_SPEED_FOR_MINIMUM_COLLISION: f32 = 256.0;
+pub const BALL_MINIMUM_COLLISION_FACTOR: f32 = 0.3;
+// Player position constants
 pub const MAXIMUM_TEAM_SIZE: usize = 5;
 pub const FORWARD_NUMBER: usize = 0;
 pub const GOALIE_NUMBER: usize = 1;
diff --git a/src/systems/collision.rs b/src/systems/collision.rs
index 618c8eb..8198216 100644
--- a/src/systems/collision.rs
+++ b/src/systems/collision.rs
@@ -1,5 +1,7 @@
 use crate::{
-    components::{collision_box, Ball, CollisionBox, MovementState, Net, Player},
+    components::{
+        collision_box, player, Ball, CollisionBox, MovementState, Net, Player, PlayerType,
+    },
     resources::Score,
     utils::Side,
 };
@@ -18,6 +20,7 @@ impl<'s> System<'s> for Collisions {
         WriteStorage<'s, MovementState>,
         ReadStorage<'s, Ball>,
         ReadStorage<'s, Player>,
+        ReadStorage<'s, PlayerType>,
         ReadStorage<'s, Net>,
         ReadStorage<'s, CollisionBox>,
         ReadStorage<'s, Transform>,
@@ -32,6 +35,7 @@ impl<'s> System<'s> for Collisions {
             mut movement_states,
             balls,
             players,
+            player_types,
             nets,
             collision_boxes,
             transforms,
@@ -46,13 +50,17 @@ impl<'s> System<'s> for Collisions {
             (&mut movement_states, &balls, &collision_boxes, &transforms).join()
         {
             // Handle collisions with players (i.e. kicks)
-            for (player, player_collision, player_transform) in
-                (&players, &collision_boxes, &transforms).join()
+            for (player, player_type, player_collision, player_transform) in
+                (&players, &player_types, &collision_boxes, &transforms).join()
             {
                 if collision_box::are_colliding(
                     ball_collision,
                     ball_transform,
-                    player_collision,
+                    &player::reduce_collision(
+                        player_collision,
+                        player_type,
+                        movement_state.velocity.norm(),
+                    ),
                     player_transform,
                 ) {
                     let center_difference =