render panel's render target in the Draw method

CHANGELOG.md

@@ -73,7 +73,8 @@ Fixes
 
 Removals
 - Marked StyleProp equality members as obsolete
-- Marked BeginDelegate and BeginImpl as obsolete
+- Marked Element.BeginDelegate and Element.BeginImpl as obsolete
+- Marked Element.DrawEarly and UiSystem.DrawEarly as obsolete
 
 ### MLEM.Extended
 Improvements

MLEM.Ui/Elements/Element.cs

@@ -185,7 +185,7 @@ namespace MLEM.Ui.Elements {
         /// Note that, when this is non-null, a new <see cref="SpriteBatch.Begin"/> call is used for this element.
         /// </summary>
         #pragma warning disable CS0618
-        [Obsolete("BeginImpl is deprecated. You can create a custom element class and override DrawEarly or Draw instead.")]
+        [Obsolete("BeginImpl is deprecated. You can create a custom element class and override Draw instead.")]
         public BeginDelegate BeginImpl;
         #pragma warning restore CS0618
         /// <summary>
@@ -990,6 +990,7 @@ namespace MLEM.Ui.Elements {
         /// <param name="effect">The effect that is used for drawing</param>
         /// <param name="depthStencilState">The depth stencil state that is used for drawing</param>
         /// <param name="matrix">The transformation matrix that is used for drawing</param>
+        [Obsolete("DrawEarly is deprecated. For custom implementations, see Panel.Draw for how to replace this method.")]
         public virtual void DrawEarly(GameTime time, SpriteBatch batch, float alpha, BlendState blendState, SamplerState samplerState, DepthStencilState depthStencilState, Effect effect, Matrix matrix) {
             foreach (var child in this.GetRelevantChildren()) {
                 if (!child.IsHidden)
@@ -1168,7 +1169,7 @@ namespace MLEM.Ui.Elements {
         /// <param name="effect">The effect used for drawing</param>
         /// <param name="depthStencilState">The depth stencil state used for drawing</param>
         /// <param name="matrix">The transform matrix used for drawing</param>
-        [Obsolete("BeginDelegate is deprecated. You can create a custom element class and override DrawEarly or Draw instead.")]
+        [Obsolete("BeginDelegate is deprecated. You can create a custom element class and override Draw instead.")]
         public delegate void BeginDelegate(Element element, GameTime time, SpriteBatch batch, float alpha, BlendState blendState, SamplerState samplerState, DepthStencilState depthStencilState, Effect effect, Matrix matrix);
 
     }

MLEM.Ui/Elements/Panel.cs

@@ -13,7 +13,6 @@ namespace MLEM.Ui.Elements {
     /// A panel element to be used inside of a <see cref="UiSystem"/>.
     /// The panel is a complex element that displays a box as a background to all of its child elements.
     /// Additionally, a panel can be set to <see cref="scrollOverflow"/> on construction, which causes all elements that don't fit into the panel to be hidden until scrolled to using a <see cref="ScrollBar"/>.
-    /// As this behavior is accomplished using a <see cref="RenderTarget2D"/>, scrolling panels need to have their <see cref="DrawEarly"/> methods called using <see cref="UiSystem.DrawEarly"/>.
     /// </summary>
     public class Panel : Element {
 
@@ -169,22 +168,13 @@ namespace MLEM.Ui.Elements {
 
         /// <inheritdoc />
         public override void Draw(GameTime time, SpriteBatch batch, float alpha, BlendState blendState, SamplerState samplerState, DepthStencilState depthStencilState, Effect effect, Matrix matrix) {
-            if (this.Texture.HasValue())
+            // draw children onto the render target if we have one
-                batch.Draw(this.Texture, this.DisplayArea, this.DrawColor.OrDefault(Color.White) * alpha, this.Scale);
-            // if we handle overflow, draw using the render target in DrawUnbound
-            if (!this.scrollOverflow || this.renderTarget == null) {
-                base.Draw(time, batch, alpha, blendState, samplerState, depthStencilState, effect, matrix);
-            } else {
-                // draw the actual render target (don't apply the alpha here because it's already drawn onto with alpha)
-                batch.Draw(this.renderTarget, this.GetRenderTargetArea(), Color.White);
-            }
-        }
-
-        /// <inheritdoc />
-        public override void DrawEarly(GameTime time, SpriteBatch batch, float alpha, BlendState blendState, SamplerState samplerState, DepthStencilState depthStencilState, Effect effect, Matrix matrix) {
-            this.UpdateAreaIfDirty();
             if (this.scrollOverflow && this.renderTarget != null) {
-                // draw children onto the render target
+                this.UpdateAreaIfDirty();
+                batch.End();
+                // force render target usage to preserve so that previous content isn't cleared
+                var lastUsage = batch.GraphicsDevice.PresentationParameters.RenderTargetUsage;
+                batch.GraphicsDevice.PresentationParameters.RenderTargetUsage = RenderTargetUsage.PreserveContents;
                 using (batch.GraphicsDevice.WithRenderTarget(this.renderTarget)) {
                     batch.GraphicsDevice.Clear(Color.Transparent);
                     // offset children by the render target's location
@@ -195,8 +185,19 @@ namespace MLEM.Ui.Elements {
                     base.Draw(time, batch, alpha, blendState, samplerState, depthStencilState, effect, trans);
                     batch.End();
                 }
+                batch.GraphicsDevice.PresentationParameters.RenderTargetUsage = lastUsage;
+                batch.Begin(SpriteSortMode.Deferred, blendState, samplerState, depthStencilState, null, effect, matrix);
+            }
+
+            if (this.Texture.HasValue())
+                batch.Draw(this.Texture, this.DisplayArea, this.DrawColor.OrDefault(Color.White) * alpha, this.Scale);
+            // if we handle overflow, draw using the render target in DrawUnbound
+            if (!this.scrollOverflow || this.renderTarget == null) {
+                base.Draw(time, batch, alpha, blendState, samplerState, depthStencilState, effect, matrix);
+            } else {
+                // draw the actual render target (don't apply the alpha here because it's already drawn onto with alpha)
+                batch.Draw(this.renderTarget, this.GetRenderTargetArea(), Color.White);
             }
-            base.DrawEarly(time, batch, alpha, blendState, samplerState, depthStencilState, effect, matrix);
         }
 
         /// <inheritdoc />

MLEM.Ui/UiSystem.cs

@@ -105,7 +105,7 @@ namespace MLEM.Ui {
         public UiControls Controls;
         /// <summary>
         /// The update and rendering statistics to be used for runtime debugging and profiling.
-        /// The metrics are reset accordingly every frame: <see cref="UiMetrics.ResetUpdates"/> is called at the start of <see cref="Update"/>, and <see cref="UiMetrics.ResetDraws"/> is called at the start of <see cref="DrawEarly"/>, or at the start of <see cref="Draw"/> if <see cref="DrawEarly"/> was not called.
+        /// The metrics are reset accordingly every frame: <see cref="UiMetrics.ResetUpdates"/> is called at the start of <see cref="Update"/>, and <see cref="UiMetrics.ResetDraws"/> is called at the start of <see cref="Draw"/>.
         /// </summary>
         public UiMetrics Metrics;
 
@@ -268,6 +268,7 @@ namespace MLEM.Ui {
         /// </summary>
         /// <param name="time">The game's time</param>
         /// <param name="batch">The sprite batch to use for drawing</param>
+        [Obsolete("DrawEarly is deprecated. Calling it is not required anymore, and there is no replacement.")]
         public void DrawEarly(GameTime time, SpriteBatch batch) {
             this.Metrics.ResetDraws();
             this.stopwatch.Restart();
@@ -284,7 +285,6 @@ namespace MLEM.Ui {
 
         /// <summary>
         /// Draws any <see cref="Element"/>s onto the screen.
-        /// Note that, when using <see cref="Panel"/>s with a scroll bar, <see cref="DrawEarly"/> needs to be called as well.
         /// </summary>
         /// <param name="time">The game's time</param>
         /// <param name="batch">The sprite batch to use for drawing</param>