nanogui: Thread: PNG and transparency

Hello,

I try to draw transparency PNG images in my nano-X application but all
the time the transparency's part of it is displayed in black..
I tried to display it on an window created by
GrNewWindow(GR_ROOT_WINDOW_ID, 0, 0, 480, 640, 0, WHITE, BLACK);

I tried with GrLoadImageFromFile plus GrDrawImageToFit and with
GrDrawImageFromFile too, and same result.
When I convert this image in .xpm and use the same code (just changing
th extension of the file to load) everything gonna be ok.

Can anybody help me please ?

Regards,

Vincent BRACH

Hello Steven, and thanks for your message,


> I have also experienced this issue.  I was able to work around it by editing the PNG file.
> 
> If you open your PNG file in an editor (I used The GIMP) and click on the area that is supposed to be transparent with the color-picker tool, you'll probably see that the RGB color values are:
> 
> R: 0
> G: 0
> B: 0
> Alpha: 0
> 
> In order for regions to appear transparent in nano-X you need to change the RGB values for the transparent area to:
> 
> R: 255
> G: 255
> B: 255
> Alpha: 0

I done some tests and I noticed some funny results : First time I used
the 0.91 :
With the "0.91" version I noticed that PNG image with RGB=0,0,0 and
Alpha=0 for transparent color was display in black (not transparent) but
PNG image with RGB=255,255,255 and Alpha=0 (or no alpha) for transparent
color was diplay with ritght transparent at this part.
After I download nano-X sources from the CVS repository Version "pre
0.92" and I noticed that there's a different comportment :
An image PNG with RGB=0,0,0 (or RGB=255,255,255) and Alpha=0 for
transparent color was right display, but normaly an image with
RGB=255,255,255 and no Alpha was display in white for parts (and not
with transparent colors). Maybe there's several difference between the
0.91 and the "pre 0.92"...
Anyway I work now with the last CVS version (pre 0.92), but this
difference is strange. Maybe a fixed bug ?

Any colors informations was took with gimp·


> (In fact, I think any region in a PNG that has a RGB value of (255,255,255) will appear transparent, even if the alpha value isn't 0.)

Right ! It's that what I noticed for the 0.91 version (but not with pre
0.92). With this last version alpha seems to be set.

> I am not experienced with photo editors, and I had to try several of them before I found one where I could figure out how to modify the RGB values of the transparent region.  Without going step-by-step, I was able to do this in The GIMP by selecting the transparent region by color, replacing its color with pure white (255,255,255), and then making the region clear again.
> 
> I'm not super experienced with nano-X so maybe someone else out there has a simpler way to fix this problem. But I hope this is helpful anyway.

Thanks again,


> Steven Vahl

Regards,

Vincent BRACH

: I try to draw transparency PNG images in my nano-X application but all
: the time the transparency's part of it is displayed in black..

Make sure you're using the CVS code, as there were earlier bugs
in transparency. v0.90 is definitely buggy.


: I tried to display it on an window created by
: GrNewWindow(GR_ROOT_WINDOW_ID, 0, 0, 480, 640, 0, WHITE, BLACK);

Using BLACK here is a bad idea, as you can't tell whether the
transparency is being drawn BLACK, or whether BLACK is
showing through.

I don't have the source code handy, but each image decoder
handles transparency differently.  I know we support GIF transparency,
I'm not sure whether PNG was added.  And below you're
saying the .xpm works.  You can check the source
looking for ".transcolor" or "->transcolor" being set
to something other than NOCOLOR.  The decoders then
don't draw a pixel when the image color matches transcolor.


: 
: I tried with GrLoadImageFromFile plus GrDrawImageToFit and with
: GrDrawImageFromFile too, and same result.

Yes, each of these use the same decoder, depending on image type.

Regards,

Greg





: When I convert this image in .xpm and use the same code (just changing
: th extension of the file to load) everything gonna be ok.
: 
: Can anybody help me please ?
: 
: Regards,
: 
: Vincent BRACH
: 
: 
: 
: 
: 
: 
:

alpha = (cr >>24 );
            //printf("%s:In Function %s Alpha=%d
\n",__FILE__,__func__,alpha);
                       if (alpha != 0) { /* skip if pixel is fully
transparent*/
                               if (clip == CLIP_VISIBLE || GdClipPoint(psd,
x, y)) {
                                       switch (psd->pixtype) {
                                       case MWPF_PALETTE:
                                       default:
                                               pixel = GdFindColor(psd, cr);
                                               break;
                                       case MWPF_TRUECOLOR8888:
                                               pixel = COLOR2PIXEL8888(cr);
                                               break;
                                       case MWPF_TRUECOLOR0888:
                                       case MWPF_TRUECOLOR888:
                           //    printf("MWPF_TRUECOLOR888\n\n");
                                               pixel = COLOR2PIXEL888(cr);
                                               break;
                                       case MWPF_TRUECOLOR565:
                       //        printf("\nMWPF_TRUECOLOR565:\n\n");
                                               pixel = COLOR2PIXEL565(cr);
                                               break;
                                       case MWPF_TRUECOLOR555:
                                               pixel = COLOR2PIXEL555(cr);
                                               break;
                                       case MWPF_TRUECOLOR332:
                                               pixel = COLOR2PIXEL332(cr);
                                               break;
                                       /*case MWPF_TRUECOLOR233:
                                               pixel = COLOR2PIXEL233(cr);
                                               break;*/
                                       }
                       //alpha=0xFF;
                    gr_background = psd->ReadPixel(psd, x, y);
        if(psd->pixtype==MWPF_TRUECOLOR8888 ||
psd->pixtype==MWPF_TRUECOLOR0888 ||psd->pixtype==MWPF_TRUECOLOR888){
                                    rb = (((pixel& 0x00ff00ff) * (alpha))
+((gr_background & 0x00ff00ff) * (0xff-alpha))) & 0xff00ff00;
                    g = (((pixel& 0x0000ff00) * (alpha)) +((gr_background &
0x0000ff00) * (0xff-alpha))) & 0x00ff0000;
                    pixel=(pixel& 0xff000000) | ((rb | g) >> 8);
                }
        else if(psd->pixtype==MWPF_TRUECOLOR565
||psd->pixtype==MWPF_TRUECOLOR555)
                {
                          bs=pixel &0x1f;
                      bb=gr_background & 0x1f;
                      gs=(pixel>>5) & 0x3f;
                      gb=(gr_background>>5)&0x3f;
                      rs=(pixel>>11)&0x1f;
                      rb=(gr_background>>11)&0x1f;
                       blue=(alpha * (bs-bb) >> 8) + bb;
                      red=(alpha * (rs-rb) >> 8) + rb;
                      green=(alpha * (gs-gb) >> 8) + gb;
                      pixel= blue | (green << 5)|(red << 11);
                }
                    psd->DrawPixel(psd, x, y,pixel);


this alpa blending concept working fine with png images.
it showing all transparency.

this changes in engine/devdraw.c file in GdDrawImage function.

regards,
Mohan.

On Thu, Jul 23, 2009 at 8:25 PM, BRACH Vincent ####@####.#### wrote:

> Hello,
>
> I try to draw transparency PNG images in my nano-X application but all
> the time the transparency's part of it is displayed in black..
> I tried to display it on an window created by
> GrNewWindow(GR_ROOT_WINDOW_ID, 0, 0, 480, 640, 0, WHITE, BLACK);
>
> I tried with GrLoadImageFromFile plus GrDrawImageToFit and with
> GrDrawImageFromFile too, and same result.
> When I convert this image in .xpm and use the same code (just changing
> th extension of the file to load) everything gonna be ok.
>
> Can anybody help me please ?
>
> Regards,
>
> Vincent BRACH
>
>
>
>
>
>
>