Re: [GD-DEVEL] Newbie transparent gif question

On Wed, 2008-04-30 at 16:24 +0200, Pierre Joye wrote:
> Hi Roger,
> 
> On Mon, Apr 28, 2008 at 9:59 AM, Roger Oberholtzer <[email protected]> wrote:
> >
> >  I am trying to create transparent gifs via gd 2.0.32 on openSUSE Linux.
> >  Nothing fancy. I set the entire image to the transparent color, and then
> >  draw on top. I only see the color I defined, not a transparent image. My
> >  viewer does support transparent gifs. I test viewed one just to be sure
> >  (konqueror in kde 3). Transparent gifs have the transparent part shown
> >  as a checker board.
> >
> >  Code snippet:
> >
> >  gdImagePtr imBase = gdImageCreate(100,100);
> >  int grey = gdImageColorAllocate(imBase, 200, 200, 200);
> 
> By the way, with palette image, the first allocated color will be the
> background/transparent color.
> 
> >  gdImageColorTransparent(imBase, grey);
> 
> This line is not required (but does not hurt).
> 
> >  gdImageFilledRectangle(imBase,  0, 0, 100,100, grey);
> 
> That neither. The image is zeroed when you create it. Zero being the
> first color in your palette, you already have a grey filled image. But
> this color is the transparent/background color.
> 
> >  Then I draw some lines or things on top in colors other than grey. Then
> >  I save the image. But the grey is shown as, well, grey. Not
> >  transparent.
> >
> >  What obvious thing have I missed?
> 
> 
> Can you show me the full code please?

I tried allocating the color I want to be transparent first, but it had
no effect. I also tried not filling the plot with grey, but that also
had no effect. 

The code is rather large. So I have provided the effective GD part. The
a, b, c, etc. bits are where I had some location references that would
just get in the way:

	// Init a plot

	gdImagePtr imBase = gdImageCreate(470, 1000);

	gdFontPtr font = gdFontGetLarge();

	int grey   = gdImageColorAllocate(imBase, 200, 200, 200);
	int black  = gdImageColorAllocate(imBase, 0, 0, 0);
	int orange = gdImageColorAllocate(imBase, 255, 165, 0);
	int yellow = gdImageColorAllocate(imBase, 255, 255, 0);

	gdImageColorTransparent(imBase, grey);

	gdImageFilledRectangle(imBase,  0, 0, 470, 1000, grey):

	gdImageSetThickness(imBase, 1);

	// Draw some lines, rectangles, polygons or text using calls like:

	gdImageFilledRectangle(imBase, a, b, c, yellow);

	gdImageLine(imBase, a, b, c, d, black);

	gdImageString(imBase, font, a, b, (unsigned char *) bLabel, black);

	gdImageFilledPolygon(imBase, points, pinfo->number_of_points, black);

	gdImagePolygon(imBase, points, pinfo->number_of_points, red);

	// Save the plot

	FILE *out = fopen(current, "wb");
	gdImageGif(imBase, out);
	fclose(out);
	gdImageDestroy(imBase);


That is pretty much it. Nothing odd. If I remove calls to
gdImageFilledRectangle, gdImageString, gdImageFilledPolygon and
gdImagePolygon, it makes no difference.




-- 
Roger Oberholtzer

OPQ Systems / Ramböll RST

Ramböll Sverige AB
Kapellgränd 7
P.O. Box 4205
SE-102 65 Stockholm, Sweden

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