8201567: QuantumRenderer modifies buffer in use by JavaFX Application Thread

Reviewed-by: kcr, arapte

Author: jgneff

modules/javafx.graphics/src/main/java/com/sun/glass/ui/Pixels.java

@@ -167,8 +167,11 @@ public final int getBytesPerComponent() {
         return this.bytesPerComponent;
     }
 
-    /*
-     * Return the original pixels buffer.
+    /**
+     * Rewinds and returns the buffer used to create this {@code Pixels} object.
+     *
+     * @return the original pixels buffer with its position set to zero and its
+     * mark discarded
      */
     public final Buffer getPixels() {
         if (this.bytes != null) {
@@ -182,6 +185,21 @@ public final Buffer getPixels() {
         }
     }
 
+    /**
+     * Returns the buffer used to create this {@code Pixels} object.
+     *
+     * @return the original pixels buffer, unmodified
+     */
+    public final Buffer getBuffer() {
+        if (this.bytes != null) {
+            return this.bytes;
+        } else if (this.ints != null) {
+            return this.ints;
+        } else {
+            throw new RuntimeException("Unexpected Pixels state.");
+        }
+    }
+
     /*
      * Return a copy of pixels as bytes.
      */

modules/javafx.graphics/src/main/java/com/sun/glass/ui/monocle/EPDFrameBuffer.java

@@ -582,9 +582,11 @@ int getByteOffset() {
      */
     ByteBuffer getOffscreenBuffer() {
         /*
-         * Allocates a direct byte buffer to avoid bug JDK-8201567,
-         * "QuantumRenderer modifies buffer in use by JavaFX Application Thread"
-         * <https://bugs.openjdk.java.net/browse/JDK-8201567>.
+         * In this case, a direct byte buffer outside of the normal heap is
+         * faster than a non-direct byte buffer on the heap. The frame rate is
+         * roughly 10 to 40 percent faster for a framebuffer with 8 bits per
+         * pixel and 40 to 60 percent faster for a framebuffer with 16 bits per
+         * pixel, depending on the device processor and screen size.
          */
         int size = xresVirtual * yres * Integer.BYTES;
         return ByteBuffer.allocateDirect(size);

modules/javafx.graphics/src/main/java/com/sun/prism/impl/QueuedPixelSource.java

@@ -100,7 +100,7 @@ public synchronized void skipLatestPixels() {
     private boolean usesSameBuffer(Pixels p1, Pixels p2) {
         if (p1 == p2) return true;
         if (p1 == null || p2 == null) return false;
-        return (p1.getPixels() == p2.getPixels());
+        return (p1.getBuffer() == p2.getBuffer());
     }
 
     /**