using glTexSubImage2D in opengl es 1.1

I am sending an opengl 3D scene across an IP link to my iPhone app built using SDK 4.1. I render the 3D scene first using FBO, read it with glReadPixels and send it to the iphone app. If I convert the pixel data received by the app to UIImage, I see it is displayed correctly. But when I use the same data in glTexSubImage2D using opengl es 1.1 (on iPhone 3G), I don't see anything. Any ideas what could be going wrong? I am using gl开发者_StackOverflow社区TexSubImage2D since glDrawPixels is not supported. Any examples/tutorials to solve this problem? Appreciate any help.

Thanks in advance.

Code -

    - (id) initWithFrame: (CGRect) frame
    {
    .....
    api = kEAGLRenderingAPIOpenGLES1;
    m_context = [[EAGLContext alloc] initWithAPI:api];

    glGenFramebuffersOES(1, &m_frameBuffer);
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, m_frameBuffer);
    glGenRenderbuffersOES(1, &m_colorRenderbuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, m_colorRenderbuffer);

    glGenTextures(1, &m_tex);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_BGRA, width, height, 0, GL_BGRA, GL_UNSIGNED_BYTE, NULL);
    ....
    }

    - (void) drawView: (CADisplayLink*) displayLink
    {
    glBindTexture(GL_TEXTURE_2D, m_tex);
    glTexSubImage2D(GL_TEXTURE_2D, 0,0,0, 
            WIDTH, HEIGHT, 
            GL_BGRA, 
            //GL_RGBA,
            GL_UNSIGNED_BYTE, 
            m_pixelData); 

const GLfloat quadVertices[] = {
    -1.0f, -1.0f, 0.0f,
    -1.0f, 1.0f, 0.0f,
    1.0f, 1.0f, 0.0f,
    1.0f, -1.0f, 0.0f,
    -1.0f, -1.0f, 0.0f
};

// Sets up an array of values for the texture coordinates.
const GLfloat quadTexcoords[] = {
    0.0f, 0.0f,
    0.0f, 1.0f,
    1.0f, 1.0f,
    1.0f, 0.0f,
    0.0f, 0.0f
};
glVertexPointer(3, GL_FLOAT, 0, quadVertices);
glEnableClientState(GL_VERTEX_ARRAY);
glTexCoordPointer(2, GL_FLOAT, 0, quadTexcoords);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, m_frameBuffer);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 5);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, m_colorRenderbuffer);

    [m_context presentRenderbuffer:GL_RENDERBUFFER_OES];
    }

Why are you using 5 vertices to make up a triangle strip? I guess what you wanted is a square made of 2 triangles, thus your strip needs only 4 vertices.

Also, in your case it would be easier just to initialize a square texture and render it like this (without using vertices):

/* do the glGenTextures() / glTexImage() / glBindTexture() dance here */
int box[] = { nXOffset, nYOffset, nWidth, nHeight };  /* define the part of the texture you're going to render */
glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_CROP_RECT_OES, box);
glDrawTexfOES(0.0f, 0.0f, 0.0f, nWidth, nHeight); /* rectangle in the screen coordinates, where to render the previously defined part of the texture */

If you're using GL_*_MIPMAP_* for GL_TEXTURE_[MIN|MAG]_FILTER (watch out for defaults!) make sure you actually provide image data for all mipmap levels.

Keep in mind that textures width and height needs to be a power of 2 on iphone/ipad platform. if it isn't you get a blank screen.