From 63029a3a27eb3ae44d802cb17b0c453e84595ade Mon Sep 17 00:00:00 2001
From: Julien Dessaux
Date: Fri, 23 Sep 2022 19:09:28 +0200
Subject: Added ball physics

---
 src/ball.zig  | 33 ++++++++++++++++++++++++++++-----
 src/game.zig  |  3 ++-
 src/utils.zig |  1 +
 3 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/src/ball.zig b/src/ball.zig
index 11737bb..f2458d4 100644
--- a/src/ball.zig
+++ b/src/ball.zig
@@ -3,21 +3,44 @@ const utils = @import("utils.zig");
 const w4 = @import("wasm4.zig");
 
 pub const Ball = struct {
+    // position of the top left corner
     x: f64,
     y: f64,
-    dx: f64,
-    dy: f64,
+    vx: f64,
+    vy: f64,
     pub fn draw(self: Ball) void {
         var y = @floatToInt(u8, std.math.round(self.y));
         var x = @floatToInt(u8, std.math.round(self.x));
-        w4.DRAW_COLORS.* = 0x4321;
+        w4.DRAW_COLORS.* = 0x2400;
         w4.blit(&ball, x, y, ball_width, ball_height, ball_flags);
     }
     pub fn resetRound(self: *Ball, side: utils.side) void {
         self.x = @intToFloat(f64, utils.startingX[@enumToInt(side)] + 4);
         self.y = 160 - 32 - 8;
-        self.dx = 0;
-        self.dy = 0;
+        self.vx = 0;
+        self.vy = -250;
+    }
+    pub fn update(self: *Ball) void {
+        self.vy += utils.gravity;
+        self.x += self.vx * utils.frequency;
+        self.y += self.vy * utils.frequency;
+        // collisions handling
+        if (self.x < 0) { // left wall
+            self.vx = -self.vx * utils.bounce;
+            self.x = 0;
+        }
+        if (self.x >= 160 - ball_width) { // right wall
+            self.vx = -self.vx * utils.bounce;
+            self.x = 160 - ball_width - 1;
+        }
+        if (self.y < 0) { // ceiling
+            self.vy = -self.vy * utils.bounce;
+            self.y = 0;
+        }
+        if (self.y >= 160 - ball_height) { // floor
+            self.vy = 0;
+            self.y = 160 - ball_height;
+        }
     }
 };
 
diff --git a/src/game.zig b/src/game.zig
index 2f3dfcd..01e3dc4 100644
--- a/src/game.zig
+++ b/src/game.zig
@@ -12,9 +12,9 @@ pub const Game = struct {
     playerSide: utils.side = undefined,
 
     pub fn draw(self: *Game) void {
-        self.ball.draw();
         self.brothers[0].draw();
         self.brothers[1].draw();
+        self.ball.draw();
         // draw the net
         w4.DRAW_COLORS.* = 0x42;
         w4.rect(78, 100, 4, 61);
@@ -34,5 +34,6 @@ pub const Game = struct {
         self.gamepads[1].update(w4.GAMEPAD2.*);
         self.brothers[0].update(self.gamepads[0]);
         self.brothers[1].update(self.gamepads[1]);
+        self.ball.update();
     }
 };
diff --git a/src/utils.zig b/src/utils.zig
index bb9eb13..6f1e850 100644
--- a/src/utils.zig
+++ b/src/utils.zig
@@ -1,4 +1,5 @@
 //----- Physics ---------------------------------------------------------------
+pub const bounce: f64 = 0.7; // energy dispersion when bouncing
 pub const gravity: f64 = 9.807; // m/s²
 pub const scale: f64 = 1.0 / 30.0; // 30 pixels == 1m
 pub const frequency: f64 = 1.0 / 60.0; // 60 fps
-- 
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