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Thread: [EGL RAGE] can only read back background from pbuffer surface

  1. #1
    Junior Member
    Join Date
    Nov 2009
    Posts
    10

    Angry [EGL RAGE] can only read back background from pbuffer surface

    I'm trying to achieve egl offscreen rendering with pbuffer surface.

    but I found out that on the read-back image, I can only see the background.

    things I draw is not visible at all. I don't know what I did wrong, I have run out of ideas.


    the documentation is so bad on EGL. no good tutorial, no anything.

    error reporting of EGL is also very very bad, creating a pbuffer surface with EGL_WINDOW_BIT as an attribute won't trigger any error, it simply doesn't work.

    I'm so mad....


    #include <QCoreApplication>
    #include <QDebug>
    #include <QImage>
    #include <GLES2/gl2.h>
    #include <EGL/egl.h>
    #include <QElapsedTimer>

    GLuint LoadShader(const char *shaderSrc, GLenum type)
    {
    GLuint shader;
    GLint compiled;

    // Create the shader object
    shader = glCreateShader(type);
    if(shader == 0)
    return 0;
    // Load the shader source
    glShaderSource(shader, 1, &shaderSrc, NULL);

    // Compile the shader
    glCompileShader(shader);
    // Check the compile status
    glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);

    if(!compiled)
    {
    GLint infoLen = 0;
    glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &infoLen);

    if(infoLen > 1)
    {
    char* infoLog = (char*)malloc(sizeof(char) * infoLen);
    glGetShaderInfoLog(shader, infoLen, NULL, infoLog);
    qDebug() << "Error compiling shader:" << infoLog;
    free(infoLog);
    }
    glDeleteShader(shader);
    return 0;
    }
    return shader;
    }

    int main(int argc, char *argv[])
    {
    GLuint renderBufferWidth = 1920;
    GLuint renderBufferHeight = 1080;
    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[23];
    pi32ConfigAttribs[0] = EGL_SURFACE_TYPE;
    pi32ConfigAttribs[1] = EGL_PBUFFER_BIT;
    pi32ConfigAttribs[2] = EGL_RENDERABLE_TYPE;
    pi32ConfigAttribs[3] = EGL_OPENGL_ES2_BIT;
    pi32ConfigAttribs[4] = EGL_CONFORMANT;
    pi32ConfigAttribs[5] = EGL_OPENGL_ES2_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] = 5;
    pi32ConfigAttribs[12] = EGL_GREEN_SIZE;
    pi32ConfigAttribs[13] = 6;
    pi32ConfigAttribs[14] = EGL_BLUE_SIZE;
    pi32ConfigAttribs[15] = 5;
    pi32ConfigAttribs[16] = EGL_ALPHA_SIZE;
    pi32ConfigAttribs[17] = 0;
    pi32ConfigAttribs[18] = EGL_DEPTH_SIZE;
    pi32ConfigAttribs[19] = 16;
    pi32ConfigAttribs[20] = EGL_LEVEL;
    pi32ConfigAttribs[21] = 0;
    pi32ConfigAttribs[22] = 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);
    }

    EGLint pbufferAttribs[5];
    pbufferAttribs[0] = EGL_WIDTH;
    pbufferAttribs[1] = renderBufferWidth;
    pbufferAttribs[2] = EGL_HEIGHT;
    pbufferAttribs[3] = renderBufferHeight;
    pbufferAttribs[4] = EGL_NONE;


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

    if (eglSurface == EGL_NO_SURFACE)
    {
    qDebug() << "surface error";
    exit(1);
    }

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

    if (eglContext == EGL_NO_CONTEXT)
    {
    qDebug() << "context error";
    exit(1);
    }

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

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

    { //init
    char* vShaderStr =
    "attribute vec4 vPosition; \n"
    "void main() \n"
    "{ \n"
    " gl_Position = vPosition; \n"
    "} \n";

    char* fShaderStr =
    "precision mediump float; \n"
    "void main() \n"
    "{ \n"
    " gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); \n"
    "} \n";
    GLuint vertexShader;
    GLuint fragmentShader;
    GLint linked;

    // Load the vertex/fragment shaders
    vertexShader = LoadShader(vShaderStr, GL_VERTEX_SHADER);
    fragmentShader = LoadShader(fShaderStr, GL_FRAGMENT_SHADER);
    // Create the program object
    programObject = glCreateProgram();
    if(programObject == 0)
    return 0;
    glAttachShader(programObject, vertexShader);
    glAttachShader(programObject, fragmentShader);
    // Bind vPosition to attribute 0
    glBindAttribLocation(programObject, 0, "vPosition");
    // Link the program
    glLinkProgram(programObject);
    // Check the link status
    glGetProgramiv(programObject, GL_LINK_STATUS, &linked);
    if(!linked)
    {
    GLint infoLen = 0;
    glGetProgramiv(programObject, GL_INFO_LOG_LENGTH, &infoLen);

    if(infoLen > 1)
    {
    char* infoLog = (char*)malloc(sizeof(char) * infoLen);
    glGetProgramInfoLog(programObject, infoLen, NULL, infoLog);
    qDebug() <<"Error linking program:" << infoLog;

    free(infoLog);
    }
    glDeleteProgram(programObject);
    }
    glClearColor(0.0f, 0.0f, 1.0f, 1.0f);
    }

    {//draw

    GLfloat vVertices[] = {0.0f, 1.5f, 0.0f,
    -0.5f, -0.5f, 0.0f,
    0.5f, -0.5f, 0.0f};

    // Set the viewport
    glViewport(0, 0, 1920, 1080);

    // Clear the color buffer
    glClear(GL_COLOR_BUFFER_BIT);
    // Use the program object
    glUseProgram(programObject);
    // Load the vertex data
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, vVertices);
    glEnableVertexAttribArray(0);
    glDrawArrays(GL_TRIANGLES, 0, 3);

    }

    int size = 4 * renderBufferHeight * renderBufferWidth;
    unsigned char *data2 = new unsigned char[size];

    eglSwapBuffers( eglDisplay, eglSurface);
    glReadPixels(0,0,renderBufferWidth,renderBufferHei ght,GL_RGBA, GL_UNSIGNED_BYTE, data2);

    qDebug() << glGetError() << eglGetError();

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

  2. #2
    Junior Member
    Join Date
    Nov 2009
    Posts
    10
    today, I ran the same program on ubuntu 14 with nvidia card and driver installed.

    and the program simply worked!

    shame on you intel!!!

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