From ac397cc5db03f73ebafc8a89c5f36a9e3accdd39 Mon Sep 17 00:00:00 2001
From: Rod Kay <rodakay5@gmail.com>
Date: Sat, 9 Dec 2023 14:58:37 +1100
Subject: [PATCH] physics.box2d.object: Add 'Z' component to 'Site' to allow
 small variations in 'Z' to prevent opengl from flipping visuals constantly
 due to all 'Z's being '0.0'.

---
 3-mid/physics/implement/box2d/source/c/box2d-object.cpp    | 2 +-
 .../source/private/box2d/box2d_physics-object.adb          | 7 +++++--
 .../source/private/box2d/box2d_physics-object.ads          | 1 +
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/3-mid/physics/implement/box2d/source/c/box2d-object.cpp b/3-mid/physics/implement/box2d/source/c/box2d-object.cpp
index 6b15fb6..f453b5d 100644
--- a/3-mid/physics/implement/box2d/source/c/box2d-object.cpp
+++ b/3-mid/physics/implement/box2d/source/c/box2d-object.cpp
@@ -158,7 +158,7 @@ b2d_Object_Site (Object*   Self)
       the_Site.y = Self->bodyDef.position (1);
     }
 
-    the_Site.z = 0.0;
+  the_Site.z = 0.0;
 
   return the_Site;
 }
diff --git a/3-mid/physics/interface/source/private/box2d/box2d_physics-object.adb b/3-mid/physics/interface/source/private/box2d/box2d_physics-object.adb
index 9014a73..f2438a8 100644
--- a/3-mid/physics/interface/source/private/box2d/box2d_physics-object.adb
+++ b/3-mid/physics/interface/source/private/box2d/box2d_physics-object.adb
@@ -184,8 +184,9 @@ is
    overriding
    function Site (Self : in Item) return Vector_3
    is
-      the_Site : constant c_math_c.Vector_3.item := b2d_Object_Site (Self.C);
+      the_Site : c_math_c.Vector_3.item := b2d_Object_Site (Self.C);
    begin
+      the_Site.z := c_math_c.Real (Self.Site_z);
       return +the_Site;
    end Site;
 
@@ -195,6 +196,7 @@ is
    is
       c_Now : aliased c_math_c.Vector_3.item := +Now;
    begin
+      Self.Site_z := Now (3);
       b2d_Object_Site_is (Self.C, c_Now'unchecked_Access);
    end Site_is;
 
@@ -238,8 +240,9 @@ is
    overriding
    function Transform (Self : in Item) return Matrix_4x4
    is
-      the_Transform : constant c_math_c.Matrix_4x4.item := b2d_Object_Transform (Self.C);
+      the_Transform : c_math_c.Matrix_4x4.item := b2d_Object_Transform (Self.C);
    begin
+      the_Transform.m32 := c_math_c.Real (Self.Site_z);
       return +the_Transform;
    end Transform;
 
diff --git a/3-mid/physics/interface/source/private/box2d/box2d_physics-object.ads b/3-mid/physics/interface/source/private/box2d/box2d_physics-object.ads
index 920e4af..cc30a04 100644
--- a/3-mid/physics/interface/source/private/box2d/box2d_physics-object.ads
+++ b/3-mid/physics/interface/source/private/box2d/box2d_physics-object.ads
@@ -61,6 +61,7 @@ private
          user_Data : access lace.Any.limited_item'Class;
 
          Dynamics  : physics.Object.safe_Dynamics;
+         Site_z    : Real := 0.0;
       end record;