android 下使用Direct Texture

要使用Direct Texture,需要有一份android系统的源码
部分C++代码如下：
#include <stdio.h>
#include <stdlib.h>
#include <GLES2/gl2.h>
#include <GLES2/gl2ext.h>
#include <EGL/egl.h>
#include <EGL/eglext.h>
#include <android/native_window.h>
#include <ui/GraphicBuffer.h>
#include <dlfcn.h>
#include <jni.h>
#include "render_native.h"

int Graphics::initGL(){

     const char * const driver_absolute_path = "/system/lib/egl/libEGL_mali.so" ;
    // On Gingerbread you have to load symbols manually from Mali driver because
    // Android EGL library has a bug.
    // From  ICE CREAM SANDWICH you can freely use the eglGetProcAddress function.
    // You might be able to get away with just eglGetProcAddress (no dlopen). Tr y it,  else revert to the following code
    void * dso = dlopen(driver_absolute_path, RTLD_LAZY);
    if (dso != 0)
    {
        LOGI( "dlopen: SUCCEEDED" );
        _eglCreateImageKHR = (PFNEGLCREATEIMAGEKHRPROC)dlsym(dso, "eglCreateImageKHR" );
        _eglDestroyImageKHR = (PFNEGLDESTROYIMAGEKHRPROC) dlsym(dso, "eglDestroyImageKHR" );
    }
    else
    {
        LOGI( "dlopen: FAILED! Loading functions in common way!" );
        _eglCreateImageKHR = (PFNEGLCREATEIMAGEKHRPROC) eglGetProcAddress( "eglCreateImageKHR" );
        _eglDestroyImageKHR = (PFNEGLDESTROYIMAGEKHRPROC) eglGetProcAddress( "eglDestroyImageKHR" );
    }

    if (_eglCreateImageKHR == NULL)
    {
        LOGE( "Error: Failed to find eglCreateImageKHR at %s:%in" , __FILE__, __LINE__);
        exit (1);
    }
    if (_eglDestroyImageKHR == NULL)
    {
        LOGE( "Error: Failed to find eglDestroyImageKHR at %s:%in" , __FILE__, __LINE__);
        exit (1);
    }
        _glEGLImageTargetTexture2DOES = (PFNGLEGLIMAGETARGETTEXTURE2DOESPROC) eglGetProcAddress( "glEGLImageTargetTexture2DOES" );
    if (_glEGLImageTargetTexture2DOES == NULL)
    {
        LOGI( "Error: Failed to find glEGLImageTargetTexture2DOES at %s:%in" , __FILE__, __LINE__);
        return 0;
    }

    graphicBuffer = new GraphicBuffer( emu_width,emu_height,
            HAL_PIXEL_FORMAT_RGBA_8888,
            GraphicBuffer::USAGE_HW_TEXTURE |
            GraphicBuffer::USAGE_HW_2D |
            GRALLOC_USAGE_SW_READ_OFTEN |
            GRALLOC_USAGE_SW_WRITE_OFTEN);

    status_t err = graphicBuffer->initCheck();
    if (err != NO_ERROR)
    {
        LOGI( "Error: %sn" , strerror (-err));
        return 0;
    }

    GGLSurface t;
    //   graphicBuffer->lock(GraphicBuffer::USAGE_SW_WRITE_OFTEN, &addr);
    graphicBuffer->lock(&t, GRALLOC_USAGE_SW_WRITE_OFTEN);

    memset (t.data,128,t.stride*t.height);
    graphicBuffer->unlock();


    // Retrieve andorid native buffer
    android_native_buffer_t* anb =graphicBuffer->getNativeBuffer();
    // create the new EGLImageKHR
    const EGLint attrs[] =
    {
        EGL_IMAGE_PRESERVED_KHR, EGL_TRUE,
        EGL_NONE, EGL_NONE
    };

    mEngine.mTexture.pEGLImage = _eglCreateImageKHR(eglGetCurrentDisplay(),
                                mEngine.nContext, EGL_NATIVE_BUFFER_ANDROID, (EGLClientBuffer)anb, attrs);
    if (mEngine.mTexture.pEGLImage == EGL_NO_IMAGE_KHR)
    {
        LOGI( "Error: eglCreateImage() failed at %s:%in" , __FILE__, __LINE__);
        return 0;
    }
    checkGlError( "eglCreateImageKHR" );
    LOGI( "create Program......." );
    GLuint gProgram = createProgram(vertex_source, fragment_source);
     checkGlError( "createProgram" );
     if (!gProgram) {
             LOGE( "Could not create program." );
             return false ;
          }
     glUseProgram(gProgram);
     vPosition = glGetAttribLocation(gProgram, "glVertex" );
         checkGlError( "glGetAttribLocation glVertex" );
     glEnableVertexAttribArray(vPosition);

    a_texCoord0 = glGetAttribLocation(gProgram, "a_texCoord0" );
        checkGlError( "glGetAttribLocation texCoord0" );
     glEnableVertexAttribArray(a_texCoord0);

     s_tex0 = glGetUniformLocation(gProgram, "s_texture0" );
        checkGlError( "glGetAttribLocation texture" );



        LOGI( "glGen Textures......." );
    glGenTextures(1, &texID);

    glDisable(GL_BLEND);
    glDisable(GL_DEPTH_TEST);
    glDisable(GL_STENCIL_TEST);
    glDisable(GL_DITHER);
    checkGlError( "glDisable" );
//  glEnable(GL_TEXTURE_2D);
//  checkGlError("glEnable(GL_TEXTURE_2D)");
    glGenTextures(1,&texID);
    checkGlError( "glGenTextures" );
     glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, texID);
//  glPixelStorei(GL_PACK_ALIGNMENT, 1);
//      glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST );
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST  );

//       glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, mEngine.mTexture.nTextureWidth, mEngine.mTexture.nTextureHeight, 0,GL_RGBA, GL_UNSIGNED_BYTE, NULL);

//  glFinish();
    _glEGLImageTargetTexture2DOES(GL_TEXTURE_2D,mEngine.mTexture.pEGLImage);

     float w = float (emu_width)  / float (mEngine.mTexture.nTextureWidth);
     float h = float (emu_height) / float (mEngine.mTexture.nTextureHeight);

         g_pos=initFloatBuffer(vertices,12);
        g_texvbo=initFloatBuffer(texCoords,8);

        glViewport(0, 0,  mEngine.nScreen_Width, mEngine.nScreen_Height);
        return 1;

}

void Graphics::renderFrame() {

//  texture=(unsigned char*)ture;
    glClearColor(0.5f, 0.5f, 0.5f, 1);
    glClear( GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);

     glUniform1i(s_tex0, 0);
     glBindBuffer(GL_ARRAY_BUFFER, g_pos);
     glVertexAttribPointer(vPosition, 3, GL_FLOAT, GL_FALSE, 0, 0);
     glBindBuffer(GL_ARRAY_BUFFER, g_texvbo);
     glVertexAttribPointer(a_texCoord0, 2, GL_FLOAT, GL_FALSE, 0, 0);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

  eglSwapBuffers(mEngine.nDisplay, mEngine.nSurface);
  ｝

void * Graphics::begin(){
    GGLSurface t;
     graphicBuffer->lock(&t,GRALLOC_USAGE_SW_WRITE_OFTEN);
    return t.data;
}
void Graphics::end(){
     graphicBuffer->unlock();
     renderFrame();
}


使用时如下：
Graphics  render;


void *buffer=render.begin();
把数据填充到buffer里
render.end();

编译时包含头文件
LOCAL_C_INCLUDES +=
    $(ANDROID_SRC_HOME)/frameworks/base/core/jni/android/graphics
    $(ANDROID_SRC_HOME)/frameworks/base/include/
    $(ANDROID_SRC_HOME)/hardware/libhardware/include
    $(ANDROID_SRC_HOME)/ system /core/include
    $(ANDROID_SRC_HOME)/frameworks/base/native/include/
    $(ANDROID_SRC_HOME)/frameworks/base/opengl/include/

链接选项：
LOCAL_LDLIBS    := -llog -lGLESv2 -lEGL -landroid  -lui -landroid_runtime  -ljnigraphics

android  Opengles 里虽然没有PBO, 但是用Direct Texture能实现类似的功能。

direct textures 的使用介绍
http: //snorp.net/2011/12/16/android-direct-texture.html

eglCreateImageKHR扩展的介绍
http: //www.khronos.org/registry/egl/extensions/KHR/EGL_KHR_image_base.txt 描述：在opengles 编程时如果用glTexImage2D /glTexSubImage2D API的话，当渲染的图片很大时，速度会变得很慢的，因为运行时会发生数据拷贝的过程，而使用opengles 的扩展glEGLImageTargetTexture2DOES可以解决这个问题，用这个扩展要用到另一个扩展 eglCreateImageKHR 。