gistfile1.m

// Storing RGBA binary buffer on disk:
            unsigned char *dest = (unsigned char*) malloc(width * height * 4 * sizeof(unsigned char));
            short *subscript = (short*) imgData;
            for (size_t i = 0; i < width * height; ++i) {
                unsigned short x = subscript[i] + 1000;
                dest[i*4] = x >> 8;
                dest[i*4+1] = x;
                dest[i*4+2] = 255;
                dest[i*4+3] = 255;
            }
            
            FILE *fp = fopen("/Users/dennda/Desktop/binary.buf", "wb");
            size_t count;
           
            if(fp == NULL) {
                printf("failed to open sample.txt\n");
                assert(0);
            }
            count = fwrite((const unsigned char*) dest, sizeof(unsigned char), width*height*4, fp);
            printf("Wrote %zu char. fclose(fp) %s.\n", width*height*4, fclose(fp) == 0 ? "succeeded" : "failed");


// Reading RGBA binary buffer & creating OGL texture:
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    FILE *fp = fopen([[[NSBundle mainBundle] pathForResource:@"binary"
                                                      ofType:@"buf"]
                                cStringUsingEncoding:NSUTF8StringEncoding],
                     "rb");
    
    size_t count = 512*512*4;
    unsigned char *buffer = malloc(count * sizeof(unsigned char));
    bzero(buffer, count);

    if (fp == NULL) {
        perror("Failed to open file \"myfile\"");
    }

    fread(buffer, sizeof(unsigned char), 512*512*4, fp);

    fclose(fp);

    glGenTextures(1, &_name);
    GetError();
    glBindTexture(GL_TEXTURE_2D, _tf_texname);
    GetError();
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);   
    GetError();
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 512, 512, 0, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
    GetError();

// Fragment shader:
    gl_FragColor = (sample.r * 256. + sample.g) / 3000.;