pbuffer vs fbo in egl-offscreen-rendering

Ich bin sehr verwirrt, egl pbuffer Oberfläche. Meiner Meinung nach, ein pbuffer Oberfläche ist eine Plattform-unabhängige Oberfläche, so wie die windows-Oberfläche oder mit der pixmap-Oberfläche. Dinge gezeichnet, die Oberfläche, obwohl nicht sichtbar, sollte in der Lage sein, wieder zu Lesen.

die Antwort auf diese Frage scheint zu bestätigen, dass mein Verständnis:

Unterschied von eglCreatePbufferSurface und eglCreatePixmapSurface mit OpenGL ES(EGL)

aber mein experiment zeigt, dass brauche ich zum erstellen eines fbo buffer zusätzlich zu pbuffer Oberfläche.

dieser code scheint zu funktionieren für mich, es schafft einen pbuffer Oberfläche und dann ein fbo.

#include <GLES2/gl2.h>
#include <EGL/egl.h>

int main(int argc, char *argv[])
{
    EGLint ai32ContextAttribs[] = { EGL_CONTEXT_CLIENT_VERSION, 2,
                                                     EGL_NONE };
    //Step 1 - Get the default display.
    EGLDisplay eglDisplay = eglGetDisplay((EGLNativeDisplayType)0);
    //Step 2 - Initialize EGL.
    eglInitialize(eglDisplay, 0, 0);
    //Step 3 - Make OpenGL ES the current API.
    eglBindAPI(EGL_OPENGL_ES_API);
    //Step 4 - Specify the required configuration attributes.
    EGLint pi32ConfigAttribs[5];
    pi32ConfigAttribs[0] = EGL_SURFACE_TYPE;
    pi32ConfigAttribs[1] = EGL_WINDOW_BIT;
    pi32ConfigAttribs[2] = EGL_RENDERABLE_TYPE;
    pi32ConfigAttribs[3] = EGL_OPENGL_ES2_BIT;
    pi32ConfigAttribs[4] = EGL_NONE;
    //Step 5 - Find a config that matches all requirements.
    int iConfigs;
    EGLConfig eglConfig;
    eglChooseConfig(eglDisplay, pi32ConfigAttribs, &eglConfig, 1, &iConfigs);

    if (iConfigs != 1) 
    {
        printf("Error: eglChooseConfig(): config not found.\n");
        exit(-1);
    }

    //Step 6 - Create a surface to draw to.
    EGLSurface eglSurface;
    eglSurface = eglCreatePbufferSurface(eglDisplay, eglConfig, NULL);

    //Step 7 - Create a context.
    EGLContext eglContext;
    eglContext = eglCreateContext(eglDisplay, eglConfig, NULL, ai32ContextAttribs);

    //Step 8 - Bind the context to the current thread
    eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext);

    GLuint fboId = 0;
    GLuint renderBufferWidth = 1920;
    GLuint renderBufferHeight = 1080;

    //Step 9 - create a framebuffer object
    glGenFramebuffers(1, &fboId);
    glBindFramebuffer(GL_FRAMEBUFFER, fboId);

    GLuint renderBuffer;
    glGenRenderbuffers(1, &renderBuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, renderBuffer);

    glRenderbufferStorage(GL_RENDERBUFFER, GL_RGB565, renderBufferWidth, renderBufferHeight);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, renderBuffer);

    GLuint depthRenderbuffer;
    glGenRenderbuffers(1, &depthRenderbuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, renderBufferWidth, renderBufferHeight);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);

    //Step 10 - check FBO status
    GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if(status != GL_FRAMEBUFFER_COMPLETE) 
    {
        printf("Problem with OpenGL framebuffer after specifying color render buffer: \n%x\n", status);
    } 
    else 
    {
        printf("FBO creation succedded\n");
    }

    int size = 4 * renderBufferHeight * renderBufferWidth;
    unsigned char *data2 = new unsigned char[size];
    //Step 11 - clear the screen in Red and read it back
    glClearColor(1.0,0.0,0.0,1.0);
    glClear(GL_COLOR_BUFFER_BIT);
    eglSwapBuffers( eglDisplay, eglSurface);
    glReadPixels(0,0,renderBufferWidth,renderBufferHeight,GL_RGBA, GL_UNSIGNED_BYTE, data2);

   ... save data2 to image ...
}

Allerdings, wenn ich entfernen Sie die fbo, und versuchen zu zeichnen, um den pbuffer direkt, sehe ich ein "segmentation fault" sofort nach dem Aufruf von glClear () - Funktion:

#include <GLES2/gl2.h>
#include <EGL/egl.h>

int main(int argc, char *argv[])
{
    EGLint ai32ContextAttribs[] = { EGL_CONTEXT_CLIENT_VERSION, 2,
                                                     EGL_NONE };
    //Step 1 - Get the default display.
    EGLDisplay eglDisplay = eglGetDisplay((EGLNativeDisplayType)0);
    //Step 2 - Initialize EGL.
    eglInitialize(eglDisplay, 0, 0);
    //Step 3 - Make OpenGL ES the current API.
    eglBindAPI(EGL_OPENGL_ES_API);
    //Step 4 - Specify the required configuration attributes.
    EGLint pi32ConfigAttribs[5];
    pi32ConfigAttribs[0] = EGL_SURFACE_TYPE;
    pi32ConfigAttribs[1] = EGL_WINDOW_BIT;
    pi32ConfigAttribs[2] = EGL_RENDERABLE_TYPE;
    pi32ConfigAttribs[3] = EGL_OPENGL_ES2_BIT;
    pi32ConfigAttribs[4] = EGL_NONE;
    //Step 5 - Find a config that matches all requirements.
    int iConfigs;
    EGLConfig eglConfig;
    eglChooseConfig(eglDisplay, pi32ConfigAttribs, &eglConfig, 1, &iConfigs);

    if (iConfigs != 1) 
    {
        printf("Error: eglChooseConfig(): config not found.\n");
        exit(-1);
    }

     //Step 6 - Create a surface to draw to.
     EGLSurface eglSurface;
     eglSurface = eglCreatePbufferSurface(eglDisplay, eglConfig, NULL);

     //Step 7 - Create a context.
     EGLContext eglContext;
     eglContext = eglCreateContext(eglDisplay, eglConfig, NULL, ai32ContextAttribs);

     //Step 8 - Bind the context to the current thread
     eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext);

     int size = 4 * renderBufferHeight * renderBufferWidth;
     unsigned char *data2 = new unsigned char[size];
     //Step 11 - clear the screen in Red and read it back
     glClearColor(1.0,0.0,0.0,1.0);
     glClear(GL_COLOR_BUFFER_BIT);
     eglSwapBuffers(    eglDisplay, eglSurface);
     glReadPixels(0,0,renderBufferWidth,renderBufferHeight,GL_RGBA, GL_UNSIGNED_BYTE, data2);

     ... save data2 to image ...
}

Meine Umgebung ist ubuntu 14 mit intel graphics/mesa.

Wissen Sie, warum ich sah die "segmentation fault"? (Ich habe in der eglcontext, das scheint zu sein, erfolgreich erstellt.) Können Sie bestätigen, dass die fbo ist gebraucht mit pbuffer Oberfläche?

EDIT: wie bereits von Reto, mein problem ist, weil der fehlende Attribute.

nach Einstellung werden diese Attribute, ich war in der Lage, Dinge zu machen die Arbeit mit opengl es 2 Kontext. Aber ich habe noch Probleme mit dem desktop opengl-Kontext.

Lesen, anstatt wieder ein rotes Bild, mit dem desktop opengl-Kontext, könnte ich nur ein transparentes Bild. hier ist meine aktuelle code:

#include <QCoreApplication>
#include <QDebug>
#include <QImage>
#include <GL/gl.h>
#include <EGL/egl.h>
#include <QElapsedTimer>

int main(int argc, char *argv[])
{
    //Step 1 - Get the default display.
    EGLDisplay eglDisplay = eglGetDisplay((EGLNativeDisplayType)0);

    //Step 2 - Initialize EGL.
    eglInitialize(eglDisplay, 0, 0);

    //Step 3 - Make OpenGL ES the current API.
    eglBindAPI(EGL_OPENGL_API);

    //Step 4 - Specify the required configuration attributes.
    EGLint pi32ConfigAttribs[5];
    pi32ConfigAttribs[0] = EGL_SURFACE_TYPE;
    pi32ConfigAttribs[1] = EGL_PBUFFER_BIT;
    pi32ConfigAttribs[2] = EGL_RENDERABLE_TYPE;
    pi32ConfigAttribs[3] = EGL_OPENGL_BIT;
    pi32ConfigAttribs[4] = EGL_CONFORMANT;
    pi32ConfigAttribs[5] = EGL_OPENGL_BIT;
    pi32ConfigAttribs[6] = EGL_COLOR_BUFFER_TYPE;
    pi32ConfigAttribs[7] = EGL_RGB_BUFFER;
    pi32ConfigAttribs[8] = EGL_LUMINANCE_SIZE;
    pi32ConfigAttribs[9] = 0;
    pi32ConfigAttribs[10] = EGL_RED_SIZE;
    pi32ConfigAttribs[11] = 8;
    pi32ConfigAttribs[12] = EGL_GREEN_SIZE;
    pi32ConfigAttribs[13] = 8;
    pi32ConfigAttribs[14] = EGL_BLUE_SIZE;
    pi32ConfigAttribs[15] = 8;
    pi32ConfigAttribs[16] = EGL_ALPHA_SIZE;
    pi32ConfigAttribs[17] = 8;
    pi32ConfigAttribs[18] = EGL_DEPTH_SIZE;
    pi32ConfigAttribs[19] = 8;
    pi32ConfigAttribs[20] = EGL_LEVEL;
    pi32ConfigAttribs[21] = 0;
    pi32ConfigAttribs[22] = EGL_BUFFER_SIZE;
    pi32ConfigAttribs[23] = 24;
    pi32ConfigAttribs[24] = EGL_NONE;
    //Step 5 - Find a config that matches all requirements.
    int iConfigs;
    EGLConfig eglConfig;
    eglChooseConfig(eglDisplay, pi32ConfigAttribs, &eglConfig, 1, &iConfigs);
    qDebug() << "egl error" << eglGetError();

    if (iConfigs != 1)
    {
        printf("Error: eglChooseConfig(): config not found.\n");
        exit(-1);
    }

    EGLint pbufferAttribs[5];
    pbufferAttribs[0] = EGL_WIDTH;
    pbufferAttribs[1] = 1920;
    pbufferAttribs[2] = EGL_HEIGHT;
    pbufferAttribs[3] = 1080;
    pbufferAttribs[4] = EGL_NONE;

    //Step 6 - Create a surface to draw to.
    EGLSurface eglSurface;
    eglSurface = eglCreatePbufferSurface(eglDisplay, eglConfig, pbufferAttribs);
    qDebug() << "egl error" << eglGetError();

    if (eglSurface == EGL_NO_SURFACE)
    {
        qDebug() << "surface issue";
    }

    //Step 7 - Create a context.
    EGLContext eglContext;
    eglContext = eglCreateContext(eglDisplay, eglConfig, NULL, NULL);
    qDebug() << "egl error" << eglGetError();

    if (eglContext == EGL_NO_CONTEXT)
    {
         qDebug() << "context issue";
    }

    //Step 8 - Bind the context to the current thread
    bool result = eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext);

    if (!result)
    {
        qDebug() << "make current error" << eglGetError();
    }
    qDebug() << "egl error" << eglGetError();

    GLuint renderBufferWidth = 1920;
    GLuint renderBufferHeight = 1080;

    QElapsedTimer benchmarkTimer;
    int size = 4 * renderBufferHeight * renderBufferWidth;
    unsigned char *data2 = new unsigned char[size];
    int i = 0;
    benchmarkTimer.start();
    while(i<1000)
    {
        glClearColor(1.0,0.0,0.0,1.0);
        glClear(GL_COLOR_BUFFER_BIT);
        eglSwapBuffers( eglDisplay, eglSurface);
        glReadPixels(0,0,renderBufferWidth,renderBufferHeight,GL_RGBA, GL_UNSIGNED_BYTE, data2);
        ++i;
    }
    qDebug() << "fps" << 1000.0*1000.0/benchmarkTimer.elapsed();

    QImage saveImage(data2, renderBufferWidth, renderBufferHeight, QImage::Format_RGBA8888_Premultiplied);
    saveImage.save("haha.png");
    QCoreApplication a(argc, argv);
    qDebug() << "done";
    return a.exec();
}