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Allow transparency in GIF images

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Thanks to preperation work done by Harald
This commit is contained in:
Robin Stuart 2020-08-03 17:13:25 +01:00
parent 13f4a3547d
commit fa0c89a43a
2 changed files with 29 additions and 11 deletions
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33
backend/gif.c
View file

@ -43,11 +43,6 @@
#define SSET "0123456789ABCDEF"
/* Index of transparent color, -1 for no transparent color
* This might be set into a variable if transparency is activated as an option
*/
#define TRANSPARENT_INDEX (-1)
typedef struct s_statestruct {
unsigned char * pOut;
unsigned char *pIn;
@ -290,6 +285,8 @@ INTERNAL int gif_pixel_plot(struct zint_symbol *symbol, char *pixelbuf) {
int paletteBitSize;
int paletteSize;
statestruct State;
int transparent_index;
int bgindex, fgindex;
unsigned char backgroundColourIndex;
unsigned char RGBCur[3];
@ -439,6 +436,9 @@ INTERNAL int gif_pixel_plot(struct zint_symbol *symbol, char *pixelbuf) {
paletteRGB[paletteIndex][2] = RGBCur[2];
paletteCount++;
if (pixelColour == '0') bgindex = paletteIndex;
if (pixelColour == '1') fgindex = paletteIndex;
}
/* Add palette index to current colour code */
(State.colourCode)[colourCount] = pixelColour;
@ -447,6 +447,23 @@ INTERNAL int gif_pixel_plot(struct zint_symbol *symbol, char *pixelbuf) {
}
State.colourCount = colourCount;
/* Set transparency */
/* Note: does not allow both transparent foreground and background -
* background takes prioroty */
transparent_index = -1;
if (strlen(symbol->fgcolour) > 6) {
if ((symbol->fgcolour[6] == '0') && (symbol->fgcolour[7] == '0')) {
// Transparent foreground
transparent_index = fgindex;
}
}
if (strlen(symbol->bgcolour) > 6) {
if ((symbol->bgcolour[6] == '0') && (symbol->bgcolour[7] == '0')) {
// Transparent background
transparent_index = bgindex;
}
}
/* find palette bit size from palette size*/
/* 1,2 -> 1, 3,4 ->2, 5,6,7,8->3 */
@ -465,7 +482,7 @@ INTERNAL int gif_pixel_plot(struct zint_symbol *symbol, char *pixelbuf) {
/* GIF signature (6) */
memcpy(outbuf, "GIF87a", 6);
if (TRANSPARENT_INDEX != -1)
if (transparent_index != -1)
outbuf[4] = '9';
fwrite(outbuf, 6, 1, gif_file);
@ -516,7 +533,7 @@ INTERNAL int gif_pixel_plot(struct zint_symbol *symbol, char *pixelbuf) {
/* A graphic control extension block is used for overlay gifs.
* This is necessary to define a transparent color.
*/
if (TRANSPARENT_INDEX != -1) {
if (transparent_index != -1) {
/* Extension Introducer = '!' */
outbuf[0] = '\x21';
/* Graphic Control Label */
@ -534,7 +551,7 @@ INTERNAL int gif_pixel_plot(struct zint_symbol *symbol, char *pixelbuf) {
outbuf[4] = 0;
outbuf[5] = 0;
/* Transparent Color Index */
outbuf[6] = (unsigned char) TRANSPARENT_INDEX;
outbuf[6] = (unsigned char) transparent_index;
/* Block Terminator */
outbuf[7] = 0;
fwrite(outbuf, 8, 1, gif_file);

7
docs/manual.txt
View file

@ -420,7 +420,7 @@ will give different results for PNG and SVG. Experimentation is advised!
Also note that these options don't work properly with Maxicode yet.
In addition the --nobackground option will simply remove the background from
PNG, SVG, EMF and EPS files.
PNG, GIF, SVG, EMF and EPS files.
4.8 Rotating the Symbol
-----------------------
@ -931,8 +931,9 @@ int main(int argc, char **argv)
return 0;
}
Background removal for PNG, SVG, EMF and EPS files can be achieved by setting
the background alpha to "00" where the values for R, G and B will be ignored:
Background removal for PNG, GIF, SVG, EMF and EPS files can be achieved by
setting the background alpha to "00" where the values for R, G and B will be
ignored:
strcpy(my_symbol->bgcolour, "55555500");