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October 30, 2020 07:08
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A function for writing marked up text to a GdkPixbuf through pangocairo
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/* An example writing text to a GdkPixbuf through pangocairo. | |
Compile by: | |
gcc -o write-text-to-pixbuf `pkg-config --cflags --libs gdk-pixbuf-2.0 pangocairo` write-text-to-pixbuf.c | |
This example is released under the MIT license. | |
Copyright 2020 Dov Grobgeld <[email protected]> | |
Permission is hereby granted, free of charge, to any person obtaining a | |
copy of this software and associated documentation files (the "Software"), | |
to deal in the Software without restriction, including without limitation | |
the rights to use, copy, modify, merge, publish, distribute, sublicense, | |
and/or sell copies of the Software, and to permit persons to whom the | |
Software is furnished to do so, subject to the following conditions: | |
The above copyright notice and this permission notice shall be included in | |
all copies or substantial portions of the Software. | |
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | |
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | |
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | |
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | |
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING | |
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER | |
DEALINGS IN THE SOFTWARE. | |
*/ | |
#include <stdio.h> | |
#include <stdarg.h> | |
#include <stdlib.h> | |
#include <cairo.h> | |
#include <pango/pango.h> | |
#include <gdk-pixbuf/gdk-pixbuf.h> | |
#include <pango/pangocairo.h> | |
static void die(const char *fmt, ...) | |
{ | |
va_list ap; | |
va_start(ap,fmt); | |
vfprintf(stderr, fmt, ap); | |
exit(-1); | |
} | |
// Create a cairo context for a GdkPixbuf. | |
// | |
// Note: | |
// - The cairo context references the same underlying data. We therefore | |
// don't need to convert back from the cairo_t to the GdkPixbuf. | |
// - cairo and GdkPixbuf have swapped byte order for the R,G,B . | |
// We therefore ned to swap R and B when setting a cairo color. | |
cairo_t *pixbuf_to_cairo(GdkPixbuf *pixbuf) | |
{ | |
cairo_format_t format = (gdk_pixbuf_get_has_alpha (pixbuf)) ? CAIRO_FORMAT_ARGB32 : CAIRO_FORMAT_RGB24; | |
gint width = gdk_pixbuf_get_width (pixbuf); | |
gint height = gdk_pixbuf_get_height (pixbuf); | |
gint stride = gdk_pixbuf_get_rowstride(pixbuf); | |
cairo_surface_t *surface = cairo_image_surface_create_for_data ( | |
gdk_pixbuf_get_pixels(pixbuf), | |
format, | |
width, | |
height, | |
stride); | |
g_assert (surface != NULL); | |
cairo_status_t status = cairo_surface_write_to_png(surface,"s.png"); | |
if (status != CAIRO_STATUS_SUCCESS) | |
die("Failed writing surface %s!\n", cairo_status_to_string(status)); | |
cairo_t *cr = cairo_create (surface); | |
return cr; | |
} | |
#if 0 | |
// Convert a cairo image surface to a pixbuf. We don't need this as | |
// the cairo context references the same pixel data! | |
GdkPixbuf *cairo_to_pixbuf(cairo_t *cr) | |
{ | |
cairo_surface_t *surface = cairo_get_target(cr); | |
bool has_alpha = cairo_image_surface_get_format(surface) == CAIRO_FORMAT_ARGB32; | |
GdkPixbuf *pixbuf = | |
gdk_pixbuf_new_from_data(cairo_image_surface_get_data(surface), | |
GDK_COLORSPACE_RGB, | |
has_alpha, | |
8, // Bits per sample | |
cairo_image_surface_get_width(surface), | |
cairo_image_surface_get_height(surface), | |
cairo_image_surface_get_stride(surface), | |
NULL, | |
NULL); | |
return pixbuf; | |
} | |
#endif | |
// A function for annotating GdkPixbuf images with text through pango | |
// | |
// fontname - A fontconfig description. E.g. "Sans Bold 15" | |
// markup - pango markup | |
// alpha - Alpha transparency A number between 0 and 1 | |
// x_align, y_align - A number between 0 and 1 | |
void write_text_to_pixbuf(GdkPixbuf *pixbuf, | |
const char *fontname, | |
PangoAlignment pango_alignment, | |
const char *colorname, | |
double alpha, | |
const char *markup, | |
int x_pos, | |
int y_pos, | |
double x_align, | |
double y_align) | |
{ | |
PangoFontDescription *font_descr = pango_font_description_from_string(fontname); | |
cairo_t *cr = pixbuf_to_cairo(pixbuf); | |
PangoContext *context = pango_cairo_create_context(cr); | |
PangoLayout *pango_layout = pango_layout_new(context); | |
pango_layout_set_font_description(pango_layout, font_descr); | |
PangoRectangle logical_rect; | |
pango_layout_set_markup(pango_layout, markup, -1); | |
pango_layout_set_alignment (pango_layout, pango_alignment); | |
pango_layout_get_extents(pango_layout, | |
NULL, | |
&logical_rect); | |
cairo_move_to(cr, | |
x_pos - logical_rect.width * x_align/PANGO_SCALE, | |
y_pos - logical_rect.height * y_align/PANGO_SCALE); | |
// Lookup the color by pango | |
PangoColor color = {0,0,0}; // black by default | |
if (!pango_color_parse(&color, | |
colorname)) | |
{ | |
fprintf(stderr, "Failed parsing color: %s!", colorname); | |
// TBD - add exception handling | |
} | |
// Swap blue and red because of differences between GdkPixbuf and | |
// cairo | |
cairo_set_source_rgba(cr, | |
color.blue/0xffff, | |
color.green/0xffff, | |
color.red/0xffff, | |
alpha); | |
pango_cairo_show_layout(cr, pango_layout); | |
cairo_surface_destroy(cairo_get_target(cr)); | |
cairo_destroy(cr); | |
g_object_unref(pango_layout); | |
g_object_unref(context); | |
} | |
int main(int argc, char **argv) | |
{ | |
int argp = 1; | |
GdkPixbuf *pixbuf = NULL; | |
const char *output_filename = "out.png"; | |
if (argp >= argc) | |
die("Need name of image!\n"); | |
const char* filename = argv[argp++]; | |
pixbuf = gdk_pixbuf_new_from_file(filename,NULL); | |
g_assert(pixbuf!=NULL); | |
write_text_to_pixbuf(pixbuf, | |
"Serif Bold 72", | |
PANGO_ALIGN_CENTER, | |
"white", | |
0.8, // alpha | |
"Jackie\nis a\ncat", | |
gdk_pixbuf_get_width(pixbuf)/2, | |
20, | |
0.5, // x_align | |
0 // y_align | |
); | |
gdk_pixbuf_save(pixbuf, | |
output_filename, | |
"png", | |
NULL, | |
NULL); | |
g_object_unref(pixbuf); | |
exit(0); | |
return(0); | |
} |
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