Gateway destinations (#21040)

* Gateway generation

* Gateway stuff

* gatewehs

* mercenaries

* play area

* Range fixes and tweaks

* weh

* Gateway UI polish

* Lots of fixes

* Knock some items off

* Fix dungeon spawning

Realistically we should probably be using a salvage job.

* wahwah

* wehvs

* expression

* weh

* eee

* a

* a

* WEH

* frfr

* Gatwey

* Fix gateway windows

* Fix gateway windows

* a

* a

* Better layer masking

* a

* a

* Noise fixes

* a

* Fix fractal calculations

* a

* More fixes

* Fixes

* Add layers back in

* Fixes

* namespaces and ftl

* Other TODO

* Fix distance

* Cleanup

* Fix test

Content.Client/Parallax/ParallaxSystem.cs

@@ -1,3 +1,4 @@
+using System.Numerics;
 using Content.Client.Parallax.Data;
 using Content.Client.Parallax.Managers;
 using Content.Shared.Parallax;
@@ -72,4 +73,56 @@ public sealed class ParallaxSystem : SharedParallaxSystem
     {
         return TryComp<ParallaxComponent>(mapUid, out var parallax) ? parallax.Parallax : Fallback;
     }
+
+    /// <summary>
+    /// Draws a texture as parallax in the specified world handle.
+    /// </summary>
+    /// <param name="worldHandle"></param>
+    /// <param name="worldAABB">WorldAABB to use</param>
+    /// <param name="sprite">Sprite to draw</param>
+    /// <param name="curTime">Current time, unused if scrolling not set</param>
+    /// <param name="position">Current position of the parallax</param>
+    /// <param name="scrolling">How much to scroll the parallax texture per second</param>
+    /// <param name="scale">Scale of the texture</param>
+    /// <param name="slowness">How slow the parallax moves compared to position</param>
+    /// <param name="modulate">Color modulation applied to drawing the texture</param>
+    public void DrawParallax(
+        DrawingHandleWorld worldHandle,
+        Box2 worldAABB,
+        Texture sprite,
+        TimeSpan curTime,
+        Vector2 position,
+        Vector2 scrolling,
+        float scale = 1f,
+        float slowness = 0f,
+        Color? modulate = null)
+    {
+        // Size of the texture in world units.
+        var size = sprite.Size / (float) EyeManager.PixelsPerMeter * scale;
+        var scrolled = scrolling * (float) curTime.TotalSeconds;
+
+        // Origin - start with the parallax shift itself.
+        var originBL = position * slowness + scrolled;
+
+        // Centre the image.
+        originBL -= size / 2;
+
+        // Remove offset so we can floor.
+        var flooredBL = worldAABB.BottomLeft - originBL;
+
+        // Floor to background size.
+        flooredBL = (flooredBL / size).Floored() * size;
+
+        // Re-offset.
+        flooredBL += originBL;
+
+        for (var x = flooredBL.X; x < worldAABB.Right; x += size.X)
+        {
+            for (var y = flooredBL.Y; y < worldAABB.Top; y += size.Y)
+            {
+                var box = Box2.FromDimensions(new Vector2(x, y), size);
+                worldHandle.DrawTextureRect(sprite, box, modulate);
+            }
+        }
+    }
 }