Help about SDL abnormal color display in VNC viewer.

[James Weatherall]

Dongxiao,

I'm afraid that the VNC List strips attachments, so I don't know what the
colour problem you're seeing is, but one common bug in X rendering code is
to assume that if the display is depth 24 that pixels are in RGB format.
Current Xvnc releases use BGR by default, which leads to red & blue being
swapped if applications mistakenly assume RGB.

Cheers,

--
Wez @ RealVNC Ltd
 

> -----Original Message-----
> From: vnc-list-admin "at" realvnc.com 
> [mailto:vnc-list-admin "at" realvnc.com] On Behalf Of ???
> Sent: 03 April 2008 09:45
> To: vnc-list "at" realvnc.com
> Subject: Help about SDL abnormal color display in VNC viewer.
> 
> Hi, all,
>     I wrote a very simple SDL drawing program under linux 
> (the code is in the first attachment), it just shows a color 
> (R=63, G=127, B=191) in a 320x240 panel. If I run the program 
> in X window, the color displays correct. But if I use VNC 
> viewer to connect the host and then run the program, the 
> color is abnormal, (see the second attached file, the left 
> part is the wrong displayed color, and the right part is the 
> correct color of R=63, G=127, B=191). Can someone help me 
> about this or is it a bug of VNC viewer?
> Thanks very much!
> 
> BTW: I am using VNC viewer free edition 4.1.1. Also I have 
> tried the latest version of VNC, this issue still exists.
> 
> Best regards,
> Xu Dongxiao
> #include <stdio.h>
> #include <stdlib.h>
> #include <SDL.h>
> 
> int main()
> {
>     uint8_t *bufp;
>     int i;
>     SDL_Surface *shared;
> 
>     if ( SDL_Init(SDL_INIT_AUDIO|SDL_INIT_VIDEO) < 0 ) {
>         fprintf(stderr, ".....SDL: %s\n", SDL_GetError());
>         exit(1);
>     }
>     atexit(SDL_Quit);
>     shared = SDL_SetVideoMode(320, 240, 24, SDL_SWSURFACE);
>     if ( shared == NULL ) {
>         fprintf(stderr, "Error to set video mode: %s\n", 
> SDL_GetError());
>         exit(1);
>     }
>     if ( SDL_MUSTLOCK(shared) ) {
>         if ( SDL_LockSurface(shared) < 0 ) {
>             return;
>         }
>     }
> 
>     bufp = (Uint8 *)shared->pixels;
>     for (i=0; i<320*240; i++) {
>         *(bufp+shared->format->Rshift/8+3*i) = 63;
>         *(bufp+shared->format->Gshift/8+3*i) = 127;
>         *(bufp+shared->format->Bshift/8+3*i) = 191;
>     }
>     if ( SDL_MUSTLOCK(shared) ) {
>         SDL_UnlockSurface(shared);
>     }
>     SDL_UpdateRect(shared, 0, 0, 320, 240);
>     while(1);
> }
> 
> [demime 1.01d removed an attachment of type image/jpeg which 
> had a name of color.jpg] 
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