经过相当多的研究和挖掘，我已找到了解决glReadPixels并如何使用PBO缓冲图像/帧以供后续处理的方法。
所以我们需要做的第一件事是在GLES2中公开一个附加功能。
在您的应用程序模块中添加一个名为cpp的新目录，然后创建一个名为GlesHelper（或任何您想要的名称）的新c文件。
然后粘贴以下代码：
#include
#include
JNIEXPORT void JNICALL
// Change
Java_com_your_full_package_name_helper_GlesHelper_glReadPixels(JNIEnv *env, jobject instance, jint x,
jint y, jint width, jint height,
jint format, jint type) {
// TODO
glReadPixels(x, y, width, height, format, type, 0);
}
接下来，您需要在项目根目录中添加一个CMakeFile。右键点击，新建文件，输入CMakeLists.txt。
然后将以下代码粘贴进去：
cmake_minimum_required(VERSION 3.4.1)
add_library( # Specifies the name of the library.
native-lib
# Sets the library as a shared library.
SHARED
# Provides a relative path to your source file(s).
src/main//cpp//GlesHelper.c )
target_link_libraries( # Specifies the target library.
native-lib
# Links the target library to the log library
# included in the NDK.
${log-lib}
GLESv2)
现在打开你的应用程序模块 build.gradle 文件，将以下内容粘贴到 Gradle 文件的 android.defaultConfig 部分。
externalNativeBuild {
// Encapsulates your CMake build configurations.
cmake {
// Provides a relative path to your CMake build script.
cppFlags "-std=c++11 -fexceptions"
arguments "-DANDROID_STL=c++_shared"
}
}
然后将此粘贴到Gradle文件的Android部分
externalNativeBuild {
// Encapsulates your CMake build configurations.
cmake {
// Provides a relative path to your CMake build script.
path "CMakeLists.txt"
}
}
现在我们已经完成了MakeFile和C语言的设置，接下来转向Java。
在您的项目中创建一个与C文件中的包相匹配的新文件，例如com_your_full_package_name_helper = com.your.full.package.name.helper。
确保这些匹配正确，同样适用于类名和函数名。
因此，您的类应该像这样：
package com.your.full.package.name.helper;
public class GlesHelper
{
public static native void glReadPixels(int x, int y, int width, int height, int format, int type);
}
由于我们在项目中添加了原生代码，因此需要使用System.loadLibrary("native-lib")加载我们的新方法。
在开始下一步之前，请将以下成员变量添加到您的Renderer中。
/**
* The PBO Ids, increase the allocate amount for more PBO's
* The more PBO's the smoother the frame rate (to an extent)
* Side affect of having more PBO's the frames you get from the PBO's will lag behind by the amount of pbo's
*/
private IntBuffer mPboIds = IntBuffer.allocate(2);;
/**
* The current PBO Index
*/
private int mCurrentPboIndex = 0;
/**
* The next PBO Index
*/
private int mNextPboIndex = 1;
现在我们需要初始化PBO，这非常简单。
// Generate the buffers for the pbo's
GLES30.glGenBuffers(mPboIds.capacity(), mPboIds);
// Loop for how many pbo's we have
for (int i = 0; i < mPboIds.capacity(); i++)
{
// Bind the Pixel_Pack_Buffer to the current pbo id
GLES30.glBindBuffer(GLES30.GL_PIXEL_PACK_BUFFER, mPboIds.get(i));
// Buffer empty data, capacity is the width * height * 4
GLES30.glBufferData(GLES30.GL_PIXEL_PACK_BUFFER, capacity, null, GLES30.GL_STATIC_READ);
}
// Reset the current buffer so we can draw properly
GLES30.glBindBuffer(GLES30.GL_PIXEL_PACK_BUFFER, 0);
在开始绘制之前，请调用此方法，它将读取像素数据到PBO中，交换缓冲区并使您可以访问像素数据。
/**
* Reads the pixels from the PBO and swaps the buffers
*/
private void readPixelsFromPBO()
{
// Bind the current buffer
GLES30.glBindBuffer(GLES30.GL_PIXEL_PACK_BUFFER, mPboIds.get(mCurrentPboIndex));
// Read pixels into the bound buffer
GlesHelper.glReadPixels(0, 0, mViewWidth, mViewHeight, GLES20.GL_RGBA, GLES30.GL_UNSIGNED_BYTE);
// Bind the next buffer
GLES30.glBindBuffer(GLES30.GL_PIXEL_PACK_BUFFER, mPboIds.get(mNextPboIndex));
// Map to buffer to a byte buffer, this is our pixel data
ByteBuffer pixelsBuffer = (ByteBuffer) GLES30.glMapBufferRange(GLES30.GL_PIXEL_PACK_BUFFER, 0, mViewWidth * mViewHeight * 4, GLES30.GL_MAP_READ_BIT);
if(mSkipFirstFrame)
{
// Skip the first frame as the PBO's have nothing in them until the second render cycle
}
// Set skip first frame to true so we can begin frame processing
mSkipFirstFrame = true;
// Swap the buffer index
mCurrentPboIndex = (mCurrentPboIndex + 1) % mPboIds.capacity();
mNextPboIndex = (mNextPboIndex + 1) % mPboIds.capacity();
// Unmap the buffers
GLES30.glUnmapBuffer(GLES30.GL_PIXEL_PACK_BUFFER);
GLES30.glBindBuffer(GLES30.GL_PIXEL_PACK_BUFFER, GLES20.GL_NONE);
GLES30.glBindFramebuffer(GLES30.GL_FRAMEBUFFER, GLES20.GL_NONE);
}
所以回到我的最初问题，我们的Redner/onDraw方法应该是这样的。
// Use the OpenGL Program for rendering
GLES20.glUseProgram(mProgram);
// If the Texture Matrix is not null
if (textureMatrix != null)
{
// Apply the Matrix
GLES20.glUniformMatrix4fv(mTexMatrixLoc, 1, false, textureMatrix, 0);
}
// Apply the Matrix
GLES20.glUniformMatrix4fv(mMVPMatrixLoc, 1, false, mMvpMatrix, 0);
// Bind the Texture
GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, textureID);
// Draw the texture
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, GLConstants.VERTEX_NUM);
// Unbind the Texture
GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, 0);
// Read from PBO
readPixelsFromPBO()
我希望这篇文章能够帮助那些遇到与glReadPixels性能问题类似的人，或者正在努力实现PBO。