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clinux-device-driverframebufferandroid-ndk-r7bpp

How to programmatically determine bpp and pixel color format of android screen?

I am trying to stream compressed raw framebuffer data to my Client application on the PC, from my Server service on Android. On the PC I want to display this raw data as streamed video in my Client's view, giving real-time view of the Android device's screen. I know how to get the resolution of the screen, but not the Bits-Per-Pixel(BPP) nor the Pixel's Color Format of the raw data programmatically at Android(Server) side. Please help.

All I could find over the Internet is native code. But I really wish to maintain the application as Java defined as possible.

From FBIOGET_VSCREENINFO over ioctl get BPP(bits-per-pixel) as follows

int main () {
    int fbfd;
    struct fb_var_screeninfo variable_info;

    fbfd=open("/dev/fb0", O_RDWR);
    //in real life, check every ioctl if it returns -1

    ioctl (fbfd, FBIOGET_VSCREENINFO, &variable_info);

    //This is the required BPP value
    switch(variable_info.bits_per_pixel) {
        case 16: //pixel format is RGB_565
            break;
        case 24: //pixel format is RGB_888
            break;
        case 32: //pixel format is RGBX_8888
            break;
    }
}
Solution

  • Finally figured out how to determine

    • BPP(bits-per-pixel) of the frame
    • Actual RGB byte orientation in the Pixel

    • Size of the framebuffer & individual frames

      int main() {
    //Structs defined in "linux/fb.h"
    struct fb_var_screeninfo vscreeninfo;
    struct fb_fix_screeninfo fscreeninfo;

    //Open the framebuffer
    fbfd=open("/dev/graphics/fb0",O_RDONLY);
    if(fbfd==-1) {
        __android_log_print(ANDROID_LOG_ERROR,ERR,
                "Could not open framebuffer fbfd=%d errno=%d",fbfd,errno);
        return errno;
    }

    //Fetch variable screen info
    ioct=ioctl(fbfd,FBIOGET_VSCREENINFO,&vscreeninfo);
    if(ioct==-1) {
        __android_log_print(ANDROID_LOG_ERROR,ERR,
                "VSCREEN-IOCTL failed ioct=%d errno=%d",ioct,errno);
        return errno;
    }

    //Fetch fixed screen info
    ioct=ioctl(fbfd,FBIOGET_FSCREENINFO,&fscreeninfo);
    if(ioct==-1) {
        __android_log_print(ANDROID_LOG_ERROR,ERR,
                "FSCREEN-IOCTL failed ioct=%d errno=%d",ioct,errno);
        return errno;
    }

    close(ioct);

    /**********************************VSCREEN DATA************************************/
    printf("\nVscreen Info:-\n");
    printf(" Xres   = %4ld | Yres   = %4ld\n",vscreeninfo.xres,vscreeninfo.yres);
    printf(" BPP    = %4ld | Height = %4ld | Width = %4ld\n",vscreeninfo.bits_per_pixel,
                                                             vscreeninfo.height,
                                                             vscreeninfo.width);
    printf(" Xres_V = %4ld | Yres_V = %4ld\n",vscreeninfo.height,vscreeninfo.width);
    printf(" Pixel format : RGBX_%ld%ld%ld%ld\n",vscreeninfo.red.length,
                                                 vscreeninfo.green.length,
                                                 vscreeninfo.blue.length,
                                                 vscreeninfo.transp.length);
    printf(" Begin of bitfields(Byte ordering):-\n");     //In my case :
    printf("  Red    : %ld\n",vscreeninfo.red.offset);    //Red    : 16
    printf("  Blue   : %ld\n",vscreeninfo.blue.offset);   //Blue   : 0
    printf("  Green  : %ld\n",vscreeninfo.green.offset);  //Green  : 8
    printf("  Transp : %ld\n",vscreeninfo.transp.offset); //Transp : 24
              //Hence orientation is : BGRT => (BGR4)RGB32 packed format
    /********************************~VSCREEN DATA************************************/

    /*********************************FSCREEN DATA************************************/
    printf("\nFscreen Info:-\n");
    printf(" Device ID : %s\n",fscreeninfo.id);
    printf(" Start of FB physical address : %ld\n",fscreeninfo.smem_start);
    printf(" Length of FB : %ld\n",fscreeninfo.smem_len); //Size of framebuffer in bytes
    printf(" Length of Line : %ld\n",fscreeninfo.line_length);
    printf(" Start of MMIO physical address : %ld\n",fscreeninfo.mmio_start);
    printf(" Length of MMIO : %ld\n",fscreeninfo.mmio_len);
    /********************************~FSCREEN DATA************************************/

    close(fbfd);
    return 0;
}

    References :-