SurfaceTexture.java revision dc02e18d154ed6271bbd7bc346de619f2698bd9a
1/* 2 * Copyright (C) 2010 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17package android.graphics; 18 19import java.lang.ref.WeakReference; 20import android.os.Handler; 21import android.os.Looper; 22import android.os.Message; 23 24/** 25 * Captures frames from an image stream as an OpenGL ES texture. 26 * 27 * <p>The image stream may come from either camera preview or video decode. A SurfaceTexture 28 * may be used in place of a SurfaceHolder when specifying the output destination of a 29 * {@link android.hardware.Camera} or {@link android.media.MediaPlayer} 30 * object. Doing so will cause all the frames from the image stream to be sent to the 31 * SurfaceTexture object rather than to the device's display. When {@link #updateTexImage} is 32 * called, the contents of the texture object specified when the SurfaceTexture was created are 33 * updated to contain the most recent image from the image stream. This may cause some frames of 34 * the stream to be skipped. 35 * 36 * <p>When sampling from the texture one should first transform the texture coordinates using the 37 * matrix queried via {@link #getTransformMatrix}. The transform matrix may change each time {@link 38 * #updateTexImage} is called, so it should be re-queried each time the texture image is updated. 39 * This matrix transforms traditional 2D OpenGL ES texture coordinate column vectors of the form (s, 40 * t, 0, 1) where s and t are on the inclusive interval [0, 1] to the proper sampling location in 41 * the streamed texture. This transform compensates for any properties of the image stream source 42 * that cause it to appear different from a traditional OpenGL ES texture. For example, sampling 43 * from the bottom left corner of the image can be accomplished by transforming the column vector 44 * (0, 0, 0, 1) using the queried matrix, while sampling from the top right corner of the image can 45 * be done by transforming (1, 1, 0, 1). 46 * 47 * <p>The texture object uses the GL_TEXTURE_EXTERNAL_OES texture target, which is defined by the 48 * OES_EGL_image_external OpenGL ES extension. This limits how the texture may be used. 49 * 50 * <p>SurfaceTexture objects may be created on any thread. {@link #updateTexImage} may only be 51 * called on the thread with the OpenGL ES context that contains the texture object. The 52 * frame-available callback is called on an arbitrary thread, so unless special care is taken {@link 53 * #updateTexImage} should not be called directly from the callback. 54 */ 55public class SurfaceTexture { 56 57 private EventHandler mEventHandler; 58 private OnFrameAvailableListener mOnFrameAvailableListener; 59 60 @SuppressWarnings("unused") 61 private int mSurfaceTexture; 62 63 /** 64 * Callback interface for being notified that a new stream frame is available. 65 */ 66 public interface OnFrameAvailableListener { 67 void onFrameAvailable(SurfaceTexture surfaceTexture); 68 } 69 70 /** 71 * Exception thrown when a surface couldn't be created or resized 72 */ 73 public static class OutOfResourcesException extends Exception { 74 public OutOfResourcesException() { 75 } 76 public OutOfResourcesException(String name) { 77 super(name); 78 } 79 } 80 81 /** 82 * Construct a new SurfaceTexture to stream images to a given OpenGL texture. 83 * 84 * @param texName the OpenGL texture object name (e.g. generated via glGenTextures) 85 */ 86 public SurfaceTexture(int texName) { 87 Looper looper; 88 if ((looper = Looper.myLooper()) != null) { 89 mEventHandler = new EventHandler(looper); 90 } else if ((looper = Looper.getMainLooper()) != null) { 91 mEventHandler = new EventHandler(looper); 92 } else { 93 mEventHandler = null; 94 } 95 nativeInit(texName, new WeakReference<SurfaceTexture>(this)); 96 } 97 98 /** 99 * Register a callback to be invoked when a new image frame becomes available to the 100 * SurfaceTexture. Note that this callback may be called on an arbitrary thread, so it is not 101 * safe to call {@link #updateTexImage} without first binding the OpenGL ES context to the 102 * thread invoking the callback. 103 */ 104 public void setOnFrameAvailableListener(OnFrameAvailableListener l) { 105 mOnFrameAvailableListener = l; 106 } 107 108 /** 109 * Update the texture image to the most recent frame from the image stream. This may only be 110 * called while the OpenGL ES context that owns the texture is bound to the thread. It will 111 * implicitly bind its texture to the GL_TEXTURE_EXTERNAL_OES texture target. 112 */ 113 public void updateTexImage() { 114 nativeUpdateTexImage(); 115 } 116 117 /** 118 * Retrieve the 4x4 texture coordinate transform matrix associated with the texture image set by 119 * the most recent call to updateTexImage. 120 * 121 * This transform matrix maps 2D homogeneous texture coordinates of the form (s, t, 0, 1) with s 122 * and t in the inclusive range [0, 1] to the texture coordinate that should be used to sample 123 * that location from the texture. Sampling the texture outside of the range of this transform 124 * is undefined. 125 * 126 * The matrix is stored in column-major order so that it may be passed directly to OpenGL ES via 127 * the glLoadMatrixf or glUniformMatrix4fv functions. 128 * 129 * @param mtx the array into which the 4x4 matrix will be stored. The array must have exactly 130 * 16 elements. 131 */ 132 public void getTransformMatrix(float[] mtx) { 133 // Note we intentionally don't check mtx for null, so this will result in a 134 // NullPointerException. But it's safe because it happens before the call to native. 135 if (mtx.length != 16) { 136 throw new IllegalArgumentException(); 137 } 138 nativeGetTransformMatrix(mtx); 139 } 140 141 protected void finalize() throws Throwable { 142 try { 143 nativeFinalize(); 144 } finally { 145 super.finalize(); 146 } 147 } 148 149 private class EventHandler extends Handler { 150 public EventHandler(Looper looper) { 151 super(looper); 152 } 153 154 @Override 155 public void handleMessage(Message msg) { 156 if (mOnFrameAvailableListener != null) { 157 mOnFrameAvailableListener.onFrameAvailable(SurfaceTexture.this); 158 } 159 return; 160 } 161 } 162 163 private static void postEventFromNative(Object selfRef) { 164 WeakReference weakSelf = (WeakReference)selfRef; 165 SurfaceTexture st = (SurfaceTexture)weakSelf.get(); 166 if (st == null) { 167 return; 168 } 169 170 if (st.mEventHandler != null) { 171 Message m = st.mEventHandler.obtainMessage(); 172 st.mEventHandler.sendMessage(m); 173 } 174 } 175 176 private native void nativeInit(int texName, Object weakSelf); 177 private native void nativeFinalize(); 178 private native void nativeGetTransformMatrix(float[] mtx); 179 private native void nativeUpdateTexImage(); 180 181 /* 182 * We use a class initializer to allow the native code to cache some 183 * field offsets. 184 */ 185 private static native void nativeClassInit(); 186 static { nativeClassInit(); } 187} 188