1 files changed, 19 insertions, 3 deletions
diff --git a/graphics/java/android/graphics/SurfaceTexture.java b/graphics/java/android/graphics/SurfaceTexture.java
index 64c209a..1fc2722 100644
--- a/graphics/java/android/graphics/SurfaceTexture.java
+++ b/graphics/java/android/graphics/SurfaceTexture.java
@@ -24,16 +24,32 @@ import android.os.Message;
 /**
  * Captures frames from an image stream as an OpenGL ES texture.
  *
- * <p>The image stream may come from either video playback or camera preview.  A SurfaceTexture may
- * be used in place of a SurfaceHolder when specifying the output destination of a MediaPlayer or
- * Camera object.  This will cause all the frames from that image stream to be sent to the
+ * <p>The image stream may come from either camera preview.  A SurfaceTexture may be used in place
+ * of a SurfaceHolder when specifying the output destination of a {@link android.hardware.Camera}
+ * object.  Doing so will cause all the frames from the image stream to be sent to the
  * SurfaceTexture object rather than to the device's display.  When {@link #updateTexImage} is
  * called, the contents of the texture object specified when the SurfaceTexture was created is
  * updated to contain the most recent image from the image stream.  This may cause some frames of
  * the stream to be skipped.
  *
+ * <p>When sampling from the texture one should first transform the texture coordinates using the
+ * matrix queried via {@link #getTransformMatrix}.  The transform matrix may change each time {@link
+ * #updateTexImage} is called, so it should be re-queried each time the texture image is updated.
+ * This matrix transforms traditional 2D OpenGL ES texture coordinate column vectors of the form (s,
+ * t, 0, 1) where s and t are on the inclusive interval [0, 1] to the proper sampling location in
+ * the streamed texture.  This transform compensates for any properties of the image stream source
+ * that cause it to appear different from a traditional OpenGL ES texture.  For example, sampling
+ * from the bottom left corner of the image can be accomplished by transforming the column vector
+ * (0, 0, 0, 1) using the queried matrix, while sampling from the top right corner of the image can
+ * be done by transforming (1, 1, 0, 1).
+ *
  * <p>The texture object uses the GL_TEXTURE_EXTERNAL_OES texture target, which is defined by the
  * OES_EGL_image_external OpenGL ES extension.  This limits how the texture may be used.
+ *
+ * <p>SurfaceTexture objects may be created on any thread.  {@link #updateTexImage} may only be
+ * called on the thread with the OpenGL ES context that contains the texture object.  The
+ * frame-available callback is called on an arbitrary thread, so unless special care is taken {@link
+ * #updateTexImage} should not be called directly from the callback.
  */
 public class SurfaceTexture {