From 8fdc3546c65601d371504ca6a40f95b837718d48 Mon Sep 17 00:00:00 2001
From: Ellpeck <me@ellpeck.de>
Date: Thu, 30 May 2024 13:24:35 +0200
Subject: [PATCH] Added the ScissorGroup element

---
 CHANGELOG.md                     |  1 +
 MLEM.Ui/Elements/Element.cs      |  1 +
 MLEM.Ui/Elements/ScissorGroup.cs | 61 ++++++++++++++++++++++++++++++++
 3 files changed, 63 insertions(+)
 create mode 100644 MLEM.Ui/Elements/ScissorGroup.cs

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d055aff..2645c33 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,6 +27,7 @@ Improvements
 Additions
 - Added the ability to set the anchor that should be used when a tooltip attaches to an element or the mouse
 - Added the ability to display tooltips using the auto-nav style even when using the mouse
+- Added the ScissorGroup element, which applies a scissor rectangle when drawing its content
 
 Improvements
 - **Include the SpriteBatchContext in OnDrawn, OnElementDrawn and OnSelectedElementDrawn**
diff --git a/MLEM.Ui/Elements/Element.cs b/MLEM.Ui/Elements/Element.cs
index 08d0245..56746a0 100644
--- a/MLEM.Ui/Elements/Element.cs
+++ b/MLEM.Ui/Elements/Element.cs
@@ -1387,6 +1387,7 @@ namespace MLEM.Ui.Elements {
         /// <param name="time">The game's time</param>
         /// <param name="batch">The sprite batch used for drawing</param>
         /// <param name="alpha">The alpha this element is drawn with</param>
+        /// <param name="context">The sprite batch context to use for drawing</param>
         public delegate void DrawCallback(Element element, GameTime time, SpriteBatch batch, float alpha, SpriteBatchContext context);
 
         /// <summary>
diff --git a/MLEM.Ui/Elements/ScissorGroup.cs b/MLEM.Ui/Elements/ScissorGroup.cs
new file mode 100644
index 0000000..2330d0d
--- /dev/null
+++ b/MLEM.Ui/Elements/ScissorGroup.cs
@@ -0,0 +1,61 @@
+using Microsoft.Xna.Framework;
+using Microsoft.Xna.Framework.Graphics;
+using MLEM.Extensions;
+using MLEM.Graphics;
+
+namespace MLEM.Ui.Elements {
+    /// <summary>
+    /// A scissor group is a <see cref="Group"/> that sets the <see cref="GraphicsDevice.ScissorRectangle"/> before drawing its content (and thus, its <see cref="Element.Children"/>), preventing them from being drawn outside of this group's <see cref="Element.DisplayArea"/>'s bounds.
+    /// </summary>
+    public class ScissorGroup : Group {
+
+        /// <summary>
+        /// The rasterizer state that this scissor group should use when drawing.
+        /// By default, <see cref="CullMode"/> is set to <see cref="CullMode.CullCounterClockwiseFace"/> in accordance with <see cref="SpriteBatch"/>'s default behavior, and <see cref="RasterizerState.ScissorTestEnable"/> is set to <see langword="true"/>.
+        /// </summary>
+        public readonly RasterizerState Rasterizer = new RasterizerState {
+            // use the default cull mode from SpriteBatch, but with scissor test enabled
+            CullMode = CullMode.CullCounterClockwiseFace,
+            ScissorTestEnable = true
+        };
+
+        /// <summary>
+        /// Creates a new scissor group with the given settings
+        /// </summary>
+        /// <param name="anchor">The group's anchor</param>
+        /// <param name="size">The group's size</param>
+        /// <param name="setHeightBasedOnChildren">Whether the group's height should be based on its children's height, see <see cref="Element.SetHeightBasedOnChildren"/>.</param>
+        public ScissorGroup(Anchor anchor, Vector2 size, bool setHeightBasedOnChildren = true) : base(anchor, size, setHeightBasedOnChildren) {}
+
+        /// <summary>
+        /// Creates a new scissor group with the given settings
+        /// </summary>
+        /// <param name="anchor">The group's anchor</param>
+        /// <param name="size">The group's size</param>
+        /// <param name="setWidthBasedOnChildren">Whether the group's width should be based on its children's width, see <see cref="Element.SetWidthBasedOnChildren"/>.</param>
+        /// <param name="setHeightBasedOnChildren">Whether the group's height should be based on its children's height, see <see cref="Element.SetHeightBasedOnChildren"/>.</param>
+        public ScissorGroup(Anchor anchor, Vector2 size, bool setWidthBasedOnChildren, bool setHeightBasedOnChildren) : base(anchor, size, setWidthBasedOnChildren, setHeightBasedOnChildren) {}
+
+        /// <inheritdoc />
+        public override void Draw(GameTime time, SpriteBatch batch, float alpha, SpriteBatchContext context) {
+            batch.End();
+
+            // apply our scissor rectangle
+            var lastScissor = batch.GraphicsDevice.ScissorRectangle;
+            batch.GraphicsDevice.ScissorRectangle = (Rectangle) this.DisplayArea.OffsetCopy(context.TransformMatrix.Translation.ToVector2());
+
+            // enable scissor test
+            var localContext = context;
+            localContext.RasterizerState = this.Rasterizer;
+            batch.Begin(localContext);
+
+            base.Draw(time, batch, alpha, localContext);
+
+            // revert back to previous behavior
+            batch.End();
+            batch.GraphicsDevice.ScissorRectangle = lastScissor;
+            batch.Begin(context);
+        }
+
+    }
+}