Contexte hors écran OpenGL ES2.0 pour le rendu FBO

Question

Je souhaite effectuer un rendu hors écran (dans un environnement de console sans WS) avec des FBO. Je sais qu'il est nécessaire de créer un contexte OpenGL, et au moins une fenêtre factice pour toute opération, donc je l'ai fait l'initialisation suivante:

// Step 1 - Get the default display. 
eglDisplay = eglGetDisplay((EGLNativeDisplayType)0); 

// Step 2 - Initialize EGL. 
EGLint iMajorVersion, iMinorVersion; 
if (!eglInitialize(eglDisplay, &iMajorVersion, &iMinorVersion)) 
{ 
    printf("Error: eglInitialize() failed.\n"); 
    goto cleanup; 
} 

// Step 3 - Make OpenGL ES the current API. 
eglBindAPI(EGL_OPENGL_ES_API); 
if (!TestEGLError("eglBindAPI")) 
{ 
    goto cleanup; 
} 

// 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; 
if (!eglChooseConfig(eglDisplay, pi32ConfigAttribs, &eglConfig, 1, &iConfigs) || (iConfigs != 1)) 
{ 
    printf("Error: eglChooseConfig() failed.\n"); 
    goto cleanup; 
} 

// Step 6 - Create a surface to draw to. 
EGLSurface eglSurface; 
eglSurface = eglCreateWindowSurface(eglDisplay, eglConfig, (EGLNativeWindowType)NULL, NULL); 
if (!TestEGLError("eglCreateWindowSurface")) goto cleanup; 

// Step 7 - Create a context. 
eglContext = eglCreateContext(eglDisplay, eglConfig, NULL, ai32ContextAttribs); 
if (!TestEGLError("eglCreateContext")) goto cleanup; 

// Step 8 - Bind the context to the current thread 
eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext); 
if (!TestEGLError("eglMakeCurrent")) goto cleanup; 

Ce type d'initialisation fonctionne sur le système cible, mais si je dessiner quelque chose dans le FBO, et après l'avoir lu (getReadPixels) toujours obtenir seulement une image noire. J'ai essayé le même code au-dessus de X11, où il échoue (egal) à l'appel eglCreateWindowSurface avec erreur: EGL_BAD_NATIVE_WINDOW WORKS, MAIS ça marche si je passe à cet appel un vrai gestionnaire de fenêtre natif X11window (Ce cas je peux relire le rendu valide image aussi)

S'il vous plaît me préciser sur quel type de surface dois-je utiliser pour le rendu FBO ?? ou qu'est-ce que je fais mal ??

Le reste du code de dessin: // init et start opengl es shanders Shaders_Init();

{ 
    // create a framebuffer object 
    glGenFramebuffers(1, &fboId); 
    glBindFramebuffer(GL_FRAMEBUFFER, fboId); 

    // create a texture object 
    GLuint textureId; 
    glGenTextures(1, &textureId); 
    glBindTexture(GL_TEXTURE_2D, textureId); 
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); 
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); //GL_LINEAR_MIPMAP_LINEAR 
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); 
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); 
    //glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP_HINT, GL_TRUE); // automatic mipmap 
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, renderBufferWidth, renderBufferHeight, 0, 
        GL_RGB, GL_UNSIGNED_BYTE, 0); 
    //glBindTexture(GL_TEXTURE_2D, 0); 


    // attach the texture to FBO color attachment point 
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, 
          GL_TEXTURE_2D, textureId, 0); 

    // 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"); 
    } 
} 





// Sets the clear color. 
// The colours are passed per channel (red,green,blue,alpha) as float values from 0.0 to 1.0 
glClearColor(0.6f, 0.8f, 1.0f, 1.0f); // clear blue 

// We're going to draw a triangle to the screen so create a vertex buffer object for our triangle 
{ 
    // Interleaved vertex data 
    GLfloat afVertices[] = { -0.4f,-0.4f,0.0f, // Position 
          0.4f ,-0.4f,0.0f, 
          0.0f ,0.4f ,0.0f}; 
    // Generate the vertex buffer object (VBO) 
    glGenBuffers(1, &ui32Vbo); 

    // Bind the VBO so we can fill it with data 
    glBindBuffer(GL_ARRAY_BUFFER, ui32Vbo); 

    // Set the buffer's data 
    unsigned int uiSize = 3 * (sizeof(GLfloat) * 3); // Calc afVertices size (3 vertices * stride (3 GLfloats per vertex)) 
    glBufferData(GL_ARRAY_BUFFER, uiSize, afVertices, GL_STATIC_DRAW); 
} 

// Draw a triangle 
{ 
    glClear(GL_COLOR_BUFFER_BIT); 
    if (!TestEGLError("glClear")) goto cleanup; 



    // First gets the location of that variable in the shader using its name 
    int i32Location = glGetUniformLocation(uiProgramObject, "myPMVMatrix"); 

    // Then passes the matrix to that variable 
    glUniformMatrix4fv(i32Location, 1, GL_FALSE, pfIdentity); 

    /* 
     Enable the custom vertex attribute at index VERTEX_ARRAY. 
     We previously binded that index to the variable in our shader "vec4 MyVertex;" 
    */ 
    glEnableVertexAttribArray(VERTEX_ARRAY); 

    // Sets the vertex data to this attribute index 
    glVertexAttribPointer(VERTEX_ARRAY, 3, GL_FLOAT, GL_FALSE, 0, 0); 

    /* 
     Draws a non-indexed triangle array from the pointers previously given. 
     This function allows the use of other primitive types : triangle strips, lines, ... 
     For indexed geometry, use the function glDrawElements() with an index list. 
    */ 
    glDrawArrays(GL_TRIANGLES, 0, 3); 
    if (!TestEGLError("glDrawArrays")) goto cleanup; 

     // get the image data 
     long imageSize = x * y * 3; 
     unsigned char *data = new unsigned char[imageSize]; 
     glReadPixels(0,0,x,y,GL_RGB,GL_UNSIGNED_BYTE,data); 

MERCI à l'avance !!!!! Cordialement, Geza

Answer 1

La solution est la suivante (sans gestion des erreurs):

#ifdef CONTEXT_ES20 
    EGLint ai32ContextAttribs[] = { EGL_CONTEXT_CLIENT_VERSION, 2, 
                  EGL_NONE }; 
    #endif 

// Step 1 - Get the default display. 
    eglDisplay = eglGetDisplay((EGLNativeDisplayType)0); 

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

    #ifdef CONTEXT_ES20 
// 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; 
    #else 
    EGLint pi32ConfigAttribs[3]; 
    pi32ConfigAttribs[0] = EGL_SURFACE_TYPE; 
    pi32ConfigAttribs[1] = EGL_WINDOW_BIT; 
    pi32ConfigAttribs[2] = EGL_NONE; 
    #endif 

// Step 5 - Find a config that matches all requirements. 
    int iConfigs; 
    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 = eglCreateWindowSurface(eglDisplay, eglConfig, 
             (EGLNativeWindowType)NULL, NULL); 

// Step 7 - Create a context. 
    #ifdef CONTEXT_ES20 
    eglContext = eglCreateContext(eglDisplay, eglConfig, NULL, 
                ai32ContextAttribs); 
    #else 
    eglContext = eglCreateContext(eglDisplay, eglConfig, NULL, NULL); 
    #endif 

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