Fix RCO menu coordinates and smooth video pacing

RCO object positions are screen-center with +Y up, but the renderer drew
them as top-left, pushing menu items off-screen. Convert to top-left in
the 480x272 design space before drawing.

Also use precise parkNanos pacing and reuse per-frame ARGB/WritableImage
buffers to remove the 1.4MB allocations per video frame.

core/src/main/java/dev/quoije/umd/media/YuvConverter.java

@@ -19,7 +19,16 @@ public final class YuvConverter {
                                       byte[] uPlane, int uStride,
                                       byte[] vPlane, int vStride) {
         int[] argb = new int[width * height];
+        yuvj420ToArgb(width, height, yPlane, yStride, uPlane, uStride, vPlane, vStride, argb);
+        return argb;
+    }
 
+    /** Converts into a caller-provided buffer of at least {@code width*height} pixels. */
+    public static void yuvj420ToArgb(int width, int height,
+                                     byte[] yPlane, int yStride,
+                                     byte[] uPlane, int uStride,
+                                     byte[] vPlane, int vStride,
+                                     int[] argb) {
         for (int row = 0; row < height; row++) {
             int yRow = row * yStride;
             int uvRow = (row >> 1) * uStride;
@@ -43,8 +52,6 @@ public final class YuvConverter {
                         | clamp(b);
             }
         }
-
-        return argb;
     }
 
     private static int clamp(int value) {

ui/src/main/java/dev/quoije/umd/ui/PlayerApp.java

@@ -35,6 +35,7 @@ import javax.sound.sampled.SourceDataLine;
 
 import java.io.IOException;
 import java.nio.file.Path;
+import java.util.concurrent.locks.LockSupport;
 
 /** JavaFX application entry point for the UMD player. */
 public final class PlayerApp extends Application {
@@ -60,6 +61,10 @@ public final class PlayerApp extends Application {
     private volatile long clockOffsetNanos = 0;
     private long pauseStartNanos = 0;
 
+    private final WritableImage[] videoImages = new WritableImage[2];
+    private final int[][] argbBuffers = new int[2][];
+    private int videoBufferIndex = 0;
+
     @Override
     public void start(Stage stage) {
         // Gradle's --args splits on whitespace; rejoin so paths with spaces work.
@@ -197,11 +202,17 @@ public final class PlayerApp extends Application {
 
                 PlaybackEngine.VideoFrame frame;
                 while ((frame = engine.nextVideoFrame()) != null) {
-                    int[] argb = YuvConverter.yuvj420ToArgb(frame.width(), frame.height(),
+                    int index = videoBufferIndex++ & 1;
+                    int[] argb = argbBuffers[index];
+                    int pixelCount = frame.width() * frame.height();
+                    if (argb == null || argb.length < pixelCount) {
+                        argb = argbBuffers[index] = new int[pixelCount];
+                    }
+                    YuvConverter.yuvj420ToArgb(frame.width(), frame.height(),
                             frame.yPlane(), frame.yStride(),
                             frame.uPlane(), frame.uStride(),
-                            frame.vPlane(), frame.vStride());
+                            frame.vPlane(), frame.vStride(), argb);
-                    blitVideo(argb, frame.width(), frame.height());
+                    blitVideo(argb, index, frame.width(), frame.height());
 
                     checkPaused();
                     long targetNanos = baseNanos + clockOffsetNanos + (frame.pts() - basePts) * 1_000_000_000L / PlaybackEngine.MPEG_TIMESTAMP;
@@ -275,10 +286,10 @@ public final class PlayerApp extends Application {
         }
     }
 
-    private static void sleepUntil(long targetNanos) throws InterruptedException {
+    private static void sleepUntil(long targetNanos) {
-        long sleepNanos = targetNanos - System.nanoTime();
+        long remaining;
-        if (sleepNanos > 0) {
+        while ((remaining = targetNanos - System.nanoTime()) > 0) {
-            Thread.sleep(sleepNanos / 1_000_000, (int) (sleepNanos % 1_000_000));
+            LockSupport.parkNanos(remaining);
         }
     }
 
@@ -330,10 +341,15 @@ public final class PlayerApp extends Application {
         }
     }
 
-    private void blitVideo(int[] argb, int width, int height) {
+    private void blitVideo(int[] argb, int index, int width, int height) {
-        WritableImage image = new WritableImage(width, height);
+        WritableImage image = videoImages[index];
+        if (image == null || (int) image.getWidth() != width || (int) image.getHeight() != height) {
+            image = new WritableImage(width, height);
+            videoImages[index] = image;
+        }
         image.getPixelWriter().setPixels(0, 0, width, height, PixelFormat.getIntArgbInstance(), argb, 0, width);
 
+        final WritableImage current = image;
         Platform.runLater(() -> {
             GraphicsContext g = videoCanvas.getGraphicsContext2D();
             double canvasWidth = videoCanvas.getWidth();
@@ -357,7 +373,7 @@ public final class PlayerApp extends Application {
             }
             double x = (canvasWidth - drawW) / 2.0;
             double y = (canvasHeight - drawH) / 2.0;
-            g.drawImage(image, x, y, drawW, drawH);
+            g.drawImage(current, x, y, drawW, drawH);
         });
     }
 

ui/src/main/java/dev/quoije/umd/ui/RcoRenderer.java

@@ -129,7 +129,14 @@ public final class RcoRenderer implements Display {
         int drawHeight = display.getHeight();
         double w = drawWidth > 0 ? drawWidth : image.getWidth();
         double h = drawHeight > 0 ? drawHeight : image.getHeight();
-        g.drawImage(image, display.getX(), display.getY(), w, h);
+
+        // RCO positions are screen-center coordinates with +Y up (OpenGL-like).
+        // Convert to top-left within the 480x272 design space.
+        double cx = display.getX();
+        double cy = display.getY();
+        double x = 240.0 + (cx - w / 2.0);
+        double y = 136.0 - (cy + h / 2.0);
+        g.drawImage(image, x, y, w, h);
         g.setGlobalAlpha(1.0);
     }