Show 3D frames only once panels over them are painted

- A frame drawn into a 3D view's window waits until Swing has painted what lies behind the floating panels, so the ground behind the height slider no longer trails the view while it moves

Model used: Claude Opus 5.5

core/src/main/java/art/arcane/iris/studio/map/GpuFrames.java

@@ -77,7 +77,7 @@ final class GpuFrames {
                 if (!windows.get().drawInto(window)) {
                     throw new IllegalStateException("GLX can't draw into the view's window");
                 }
-                return drawing.drawInto(new GpuWindowFrame(windows.get(), window, screen.seeThrough()));
+                return drawing.drawInto(new GpuWindowFrame(screen.seeThrough()));
             } catch (RuntimeException failure) {
                 gpu.stopDrawingIntoWindows(failure);
                 return Optional.empty();
@@ -85,6 +85,31 @@ final class GpuFrames {
         });
     }
 
+    /**
+     * Puts the last frame drawn into the view's window on screen. Another view may have drawn into its own window
+     * since, so the view's window is made current again first.
+     *
+     * @return false when the window didn't take it, and the caller should draw a picture instead
+     */
+    static boolean showOnScreen(ScreenTarget screen) {
+        return onCard(gpu -> {
+            Optional<GlxDisplay> windows = gpu.windows();
+            long window = screen.canvas().window();
+            if (windows.isEmpty() || window == 0L) {
+                return Optional.<Boolean>empty();
+            }
+            try {
+                if (!windows.get().drawInto(window) || !windows.get().show(window)) {
+                    throw new IllegalStateException("The window didn't take the frame");
+                }
+                return Optional.of(true);
+            } catch (RuntimeException failure) {
+                gpu.stopDrawingIntoWindows(failure);
+                return Optional.<Boolean>empty();
+            }
+        }).isPresent();
+    }
+
     static void failOnError() {
         int error = glGetError();
         if (error != GL_NO_ERROR) {
@@ -119,7 +144,7 @@ final class GpuFrames {
         return offScreen;
     }
 
-    private static Optional<OrbitPicture> onCard(CardWork work) {
+    private static <T> Optional<T> onCard(CardWork<T> work) {
         if (failed) {
             return Optional.empty();
         }
@@ -145,7 +170,7 @@ final class GpuFrames {
     }
 
     @FunctionalInterface
-    private interface CardWork {
-        Optional<OrbitPicture> drawOn(GpuContext gpu);
+    private interface CardWork<T> {
+        Optional<T> drawOn(GpuContext gpu);
     }
 }

core/src/main/java/art/arcane/iris/studio/map/GpuWindowFrame.java

@@ -28,13 +28,12 @@ import static org.lwjgl.opengl.GL30.*;
 
 /**
  * A frame drawn straight into a view's window. Of what was drawn, only the patches Swing paints where panels float
- * over the window are read back. Only for the GPU thread.
+ * over the window are read back. The frame waits in the window's back buffer until {@link GpuFrames#showOnScreen},
+ * so it can go on screen together with its patches. Only for the GPU thread.
  */
 final class GpuWindowFrame implements GpuFrameTarget {
     private static final int WINDOW_FRAMEBUFFER = 0;
 
-    private final GlxDisplay windows;
-    private final long window;
     private final List<Rectangle> seeThrough;
     private int width;
     private int height;
@@ -42,9 +41,7 @@ final class GpuWindowFrame implements GpuFrameTarget {
     /**
      * @param seeThrough the parts of the view panels float over, which Swing paints instead of the window
      */
-    GpuWindowFrame(GlxDisplay windows, long window, List<Rectangle> seeThrough) {
-        this.windows = windows;
-        this.window = window;
+    GpuWindowFrame(List<Rectangle> seeThrough) {
         this.seeThrough = seeThrough;
     }
 
@@ -62,12 +59,7 @@ final class GpuWindowFrame implements GpuFrameTarget {
 
     @Override
     public OrbitPicture finish(OrbitProjection projection, double depthRange) {
-        OrbitPicture picture = OrbitPicture.onScreen(width, height, readPatches(),
-                GpuFrameTarget.depthInMiddle(projection, depthRange, width, height));
-        if (!windows.show(window)) {
-            throw new IllegalStateException("The window didn't take the frame");
-        }
-        return picture;
+        return OrbitPicture.onScreen(width, height, readPatches(), GpuFrameTarget.depthInMiddle(projection, depthRange, width, height));
     }
 
     private List<PicturePatch> readPatches() {

core/src/main/java/art/arcane/iris/studio/map/OrbitViewport.java

@@ -31,6 +31,7 @@ import java.awt.Graphics2D;
 import java.awt.GraphicsConfiguration;
 import java.awt.Point;
 import java.awt.RenderingHints;
+import java.awt.Toolkit;
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
 import java.awt.event.ComponentAdapter;
@@ -338,7 +339,7 @@ final class OrbitViewport extends JComponent {
         renderThread.execute(() -> {
             OrbitPicture drawn = draw(frameScene, screen, frameCamera, width, height, covered);
             boolean missedScreen = screen != null && !drawn.onScreen();
-            EventQueue.invokeLater(() -> finishFrame(frameScene, frameCamera, drawn, missedScreen, requestedAtNanos));
+            EventQueue.invokeLater(() -> finishFrame(frameScene, frameCamera, screen, drawn, missedScreen, requestedAtNanos));
         });
     }
 
@@ -380,25 +381,40 @@ final class OrbitViewport extends JComponent {
 
     /**
      * Until the card is opened, nothing knows whether frames can go into the window; the first picture opens it. A
-     * frame that should have gone into the window but couldn't isn't tried again right away. The next frame is asked
-     * for before this one's patches are painted, so the card draws while Swing paints.
+     * frame that should have gone into the window but couldn't isn't tried again right away. A frame for a scene
+     * replaced meanwhile is never shown.
      */
-    private void finishFrame(OrbitScene frameScene, OrbitCamera frameCamera, OrbitPicture drawn, boolean missedScreen,
-                             long requestedAtNanos) {
+    private void finishFrame(OrbitScene frameScene, OrbitCamera frameCamera, ScreenTarget screen, OrbitPicture drawn,
+                             boolean missedScreen, long requestedAtNanos) {
         rendering = false;
         measureFrameTime(System.nanoTime() - requestedAtNanos);
-        boolean shown = frameScene == scene;
-        if (shown) {
+        if (frameScene == scene) {
             takePicture(drawn, frameCamera);
+            paintPicture(drawn);
+            showInWindow(screen, drawn);
         }
         boolean canGoOnScreen = !missedScreen && canvas != null && !canvas.isVisible() && drawsOnScreen();
         if (renderAgain || drawn.catchingUp() || canGoOnScreen) {
             renderAgain = false;
             requestFrame();
         }
-        if (shown) {
-            paintPicture(drawn);
+    }
+
+    /**
+     * A frame in the window only goes on screen once Swing has painted its patches, or the panels floating over the
+     * window would show the frame before. Swing and the card reach the screen through separate connections, so
+     * Swing's is flushed first. The render thread shows the frame before it draws the next one into the window.
+     */
+    private void showInWindow(ScreenTarget screen, OrbitPicture drawn) {
+        if (!drawn.onScreen()) {
+            return;
         }
+        Toolkit.getDefaultToolkit().sync();
+        renderThread.execute(() -> {
+            if (!GpuFrames.showOnScreen(screen)) {
+                EventQueue.invokeLater(this::requestFrame);
+            }
+        });
     }
 
     // A whole picture replaces the window until frames go into it again.