我正在尝试将glsurfaceview的输出呈现给sdCard上的PNG，并且遇到了一些问题。我花了几天时间尝试对类似的SO查询进行排序，这仅仅高于我的专业水平。有人请帮助我通过下面的日志排序，看看我可能会出错。
非常感谢。
日志：
12-16 12:09:18.831: E/AndroidRuntime(29864): FATAL EXCEPTION: GLThread 2712
12-16 12:09:18.831: E/AndroidRuntime(29864): java.nio.BufferUnderflowException
12-16 12:09:18.831: E/AndroidRuntime(29864): at java.nio.Buffer.checkGetBounds(Buffer.java:177)
12-16 12:09:18.831: E/AndroidRuntime(29864): at java.nio.DirectByteBuffer.get(DirectByteBuffer.java:66)
12-16 12:09:18.831: E/AndroidRuntime(29864): at java.nio.IntToByteBufferAdapter.get(IntToByteBufferAdapter.java:105)
12-16 12:09:18.831: E/AndroidRuntime(29864): at java.nio.IntBuffer.get(IntBuffer.java:234)
12-16 12:09:18.831: E/AndroidRuntime(29864): at com.research.glgrade.GLLayer.grabPixels(GLLayer.java:865)
12-16 12:09:18.831: E/AndroidRuntime(29864): at com.research.glgrade.GLLayer.saveScreenShot(GLLayer.java:810)
12-16 12:09:18.831: E/AndroidRuntime(29864): at com.research.glgrade.GLLayer.onDrawFrame(GLLayer.java:794)
12-16 12:09:18.831: E/AndroidRuntime(29864): at android.opengl.GLSurfaceView$GLThread.guardedRun(GLSurfaceView.java:1527)
12-16 12:09:18.831: E/AndroidRuntime(29864): at android.opengl.GLSurfaceView$GLThread.run(GLSurfaceView.java:1240)
12-16 12:09:26.849: I/Choreographer(29864): Skipped 478 frames! The application may be doing too much work on its main thread.
这是我目前的代码： 来自主要活动：
GlobalVariables.setPrint("true");
mView.requestRender();
来自渲染类
public void onDrawFrame(GL10 glUnused ) {
GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT);
final String vertexShader = getVertexShader();
final String fragmentShader = getFragmentShader();
final int vertexShaderHandle = ShaderHelper.compileShader(
GLES20.GL_VERTEX_SHADER, vertexShader);
final int fragmentShaderHandle = ShaderHelper.compileShader(
GLES20.GL_FRAGMENT_SHADER, fragmentShader);
mProgramHandle = ShaderHelper.createAndLinkProgram(vertexShaderHandle,
fragmentShaderHandle, new String[] { "a_Position",
"a_TexCoordinate" });
// Set our per-vertex lighting program.
GLES20.glUseProgram(mProgramHandle);
// Set program handles for cube drawing.
mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgramHandle,
"u_MVPMatrix");
mTextureUniformHandle0 = GLES20.glGetUniformLocation(mProgramHandle,
"u_Texture0");
mTextureUniformHandle1 = GLES20.glGetUniformLocation(mProgramHandle,
"u_Texture1");
GLES20.glActiveTexture(GLES20.GL_TEXTURE4);
// Bind the texture to this unit.
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, mTextureDataHandle4);
// Tell the texture uniform sampler to use this texture in the shader by
// binding to texture unit 3.
GLES20.glUniform1i(mTextureUniformHandle4, 4);
// Draw some cubes.
Matrix.setIdentityM(mModelMatrix, 0);
Matrix.translateM(mModelMatrix, 0, mTransX, mTransY, mAngle*0.05f);
Matrix.rotateM(mModelMatrix, 0, 0.0f, 1.0f, 1.0f, 0.0f);
drawCube();
int width_surfacea = width_surface ;
int height_surfacea = height_surface ;
if ( GlobalVariables.getPrint() != "false" ) {
String mFrameCount = "1";
saveScreenShot(0, 0, width_surfacea, height_surfacea, "/save/test.png");
GlobalVariables.setPrint("false");
}
}
public void saveScreenShot(int x, int y, int w, int h, String filename) {
Bitmap bmp = grabPixels(x, y, w, h);
try {
String path = Environment.getExternalStorageDirectory() + "/" + filename;
File file = new File(path);
file.createNewFile();
FileOutputStream fos = new FileOutputStream(file);
bmp.compress(CompressFormat.PNG, 100, fos);
fos.flush();
fos.close();
} catch (Exception e) {
e.printStackTrace();
}
}
public Bitmap grabPixels(int x, int y, int w, int h) {
int screenshotSize = w * h;
ByteBuffer bb = ByteBuffer.allocateDirect(screenshotSize * 3);
bb.order(ByteOrder.nativeOrder());
bb.position(0);
GLES20.glReadPixels(0, 0, w, h, GLES20.GL_RGB, GLES20.GL_UNSIGNED_BYTE, bb);
int pixelsBuffer[] = new int[screenshotSize];
bb.asIntBuffer().get(pixelsBuffer);
bb = null;
Bitmap bitmap = Bitmap.createBitmap(w, h, Bitmap.Config.RGB_565);
bitmap.setPixels(pixelsBuffer, screenshotSize-w, -w, 0, 0, w, h);
pixelsBuffer = null;
short sBuffer[] = new short[screenshotSize];
ShortBuffer sb = ShortBuffer.wrap(sBuffer);
bitmap.copyPixelsToBuffer(sb);
//Making created bitmap (from OpenGL points) compatible with Android bitmap
for (int i = 0; i < screenshotSize; ++i) {
short v = sBuffer[i];
sBuffer[i] = (short) (((v&0x1f) << 11) | (v&0x7e0) | ((v&0xf800) >> 11));
}
sb.rewind();
bitmap.copyPixelsFromBuffer(sb);
return bitmap;
}
答案 0 :(得分：2)
您的阵列长度不匹配。 代码行：
bb.asIntBuffer().get(pixelsBuffer);
导致异常，因为bb.asIntBuffer（）的长度仅为（w * h * 3），而pixelsBuffer的长度为w * h * 4（当然我说的是字节）。 所以get（）会抛出异常（根据文档） http://developer.android.com/reference/java/nio/IntBuffer.html#get%28int[]%29
更新
尝试此代码（警告：我甚至没有尝试编译它）：
public Bitmap grabPixels(int x, int y, int w, int h) {
// Allocate byte array of H*W size assuming that we retrieve only R,G and B values
ByteBuffer byteBuffer = ByteBuffer.allocateDirect(screenshotSize * 3);
byteBuffer.order(ByteOrder.nativeOrder());
byteBuffer.position(0);
// Read RGB values to our byte array
GLES20.glReadPixels(x, y, w, h, GLES20.GL_RGB, GLES20.GL_UNSIGNED_BYTE, byteBuffer);
//Now we need to convert the 24bit RGB data to ARGB8888 format
// I like arrays, they are honest :)
byte[] pixelBuffer = byteBuffer.array();
// This is an array that we going to use as backend for the bitmap
int[] finalPixels = new int[w*h];
// Let the magic flow
int j = 0;
for (int i = 0; i < pixelBuffer.length; i += 3) {
byte red = pixelBuffer[i];
byte green = pixelBuffer[i+1];
byte blue = pixelBuffer[i+2];
finalPixels[j++] = 0xFF000000 | ((int)blue << 16) | ((int)green << 8) | red;
}
// Create a bitmap of ARGB_8888
return Bitmap.createBitmap(finalPixels, w, h, Bitmap.Config.ARGB_8888);
}
答案 1 :(得分：2)
可以找到用于从MPEG文件中提取帧的示例代码on bigflake。视频帧使用GL进行渲染，saveFrame()函数使用glReadPixels()和Bitmap将其作为PNG保存到磁盘。
您需要注意一些相当重要的性能缺陷;有关如何最好地使用NIO的一些注释，请参阅saveFrame()中的注释。您还要确保您的EGLConfig符合您的像素读取格式（如果源格式和目标格式不相同，glReadPixels()可能会变慢）。
更新：现在Grafika中的实施稍微更为一般 - 请参阅EglSurfaceBase#saveFrame()。
答案 2 :(得分：1)
我认为ByteBuffer bb = ByteBuffer.allocateDirect(screenshotSize * 3);是错误的。
它应该是ByteBuffer bb = ByteBuffer.allocateDirect(screenshotSize * 4);