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56b5a7eeca
One problem is, that tolua/lua does not handle plain data pointers
properly. Therefore something like
local surface = cairo_image_surface_create_for_data(
imlib_image_get_data_for_reading_only(), ..
will fail using the lua bindings. Hence this wrapper, which adds
a function which be used to draw an imlib image to a cairo surface.
This also addresses another issue, drawing images with a transparent
background (e.g. gifs or pngs) to the cairo surface properly. Apparently
the image format of imlib is incompatible to cairos which uses
pre-multiplied data. This is also explained in the cairo documentation.
A fix for this issue is to blend the image with another alpha mask to
get the correct values. The code and explanation for this was taken from
http://lists.cairographics.org/archives/cairo/2008-March/013492.html
Executive Summary: This wrapper function can load (transparent) images
(e.g. gif or png) from a file by using imlib and draw them on a cairo
surface.
80 lines
2.6 KiB
C
80 lines
2.6 KiB
C
/* -*- mode: c; c-basic-offset: 4; tab-width: 4; indent-tabs-mode: t -*-
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*
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* Conky, a system monitor, based on torsmo
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*
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* Please see COPYING for details
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*
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* Copyright (c) 2005-2012 Brenden Matthews, Philip Kovacs, et. al.
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* (see AUTHORS)
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* All rights reserved.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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#ifndef _LIBCAIRO_IMAGE_HELPER_H_
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#define _LIBCAIRO_IMAGE_HELPER_H_
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#include <cairo.h>
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#include <Imlib2.h>
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void
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cairo_draw_image(const char * file, cairo_surface_t * cs, int x, int y,
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double scale_x, double scale_y,
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double * return_scale_w, double * return_scale_h)
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{
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Imlib_Image * image = imlib_load_image(file);
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if (! image) { return; }
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imlib_context_set_image(image);
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int w = imlib_image_get_width(), h = imlib_image_get_height();
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double scaled_w = *return_scale_w = scale_x * (double)w
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, scaled_h = *return_scale_h = scale_y * (double)h;
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/* create temporary image */
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Imlib_Image premul = imlib_create_image(scaled_w, scaled_h);
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/* FIXME: add error handling */
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/* fill with opaque black */
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imlib_context_set_image(premul);
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imlib_context_set_color(0, 0, 0, 255);
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imlib_image_fill_rectangle(0, 0, scaled_w, scaled_h);
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/* blend source image on top -
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* in effect this multiplies the rgb values by alpha */
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imlib_blend_image_onto_image(image, 0, 0, 0, w, h, 0, 0, scaled_w, scaled_h);
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/* and use the alpha channel of the source image */
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imlib_image_copy_alpha_to_image(image, 0, 0);
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/* now pass the result to cairo */
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cairo_surface_t * result = cairo_image_surface_create_for_data(
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(void *) imlib_image_get_data_for_reading_only(),
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CAIRO_FORMAT_ARGB32, scaled_w, scaled_h, sizeof(DATA32) * scaled_w);
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cairo_t * cr = cairo_create(cs);
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cairo_set_source_surface(cr, result, x, y);
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cairo_paint(cr);
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imlib_context_set_image(image);
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imlib_free_image();
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imlib_context_set_image(premul);
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imlib_free_image();
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cairo_destroy(cr);
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cairo_surface_destroy(result);
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}
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#endif /* _LIBCAIRO_IMAGE_HELPER_H_ */
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