C Imlib blend two images with alpha - c

Question

I'm trying to blend two images with alpha using Imlib library (this code is changing wallpaper).
So far I got this:
#include <stdio.h>
#include <X11/Xlib.h>
#include <Imlib2.h>
int main( int argc, char **argv )
{
Display *display;
Pixmap pixmap;
Window root;
Screen *screen;
int width,
height,
w1,
w2,
h1,
h2;
Imlib_Image img,
img2;
// loading images
img = imlib_load_image( "/usr/share/wallpapers/wallpaper1.jpg" );
img2 = imlib_load_image( "/usr/share/wallpapers/wallpaper2.jpg" );
if( !img || !img2 ) {
printf( "Unable to load image.\n" );
return 1;
}
// open display, get screen and root window
display = XOpenDisplay(NULL);
screen = DefaultScreenOfDisplay( display );
root = DefaultRootWindow( display );
width = screen->width;
height = screen->height;
// create pixmap
pixmap = XCreatePixmap( display, root, width, height, DefaultDepthOfScreen(screen) );
// #S == BLENDING 1 =========================
imlib_context_set_image( img );
w1 = imlib_image_get_width();
h1 = imlib_image_get_height();
imlib_context_set_image( img2 );
w2 = imlib_image_get_width();
h2 = imlib_image_get_height();
imlib_context_set_image( img );
imlib_blend_image_onto_image( img2, 0, 0, 0, width, height, 0, 0, width, height );
//imlib_blend_image_onto_image( img2, 0, 0, 0, w2, h2, 0, 0, w1, h1 );
// #E == BLENDING 1 =========================
// setting context
imlib_context_set_image( img );
imlib_context_set_display( display );
imlib_context_set_visual( DefaultVisualOfScreen(screen) );
imlib_context_set_colormap( DefaultColormapOfScreen(screen) );
imlib_context_set_drawable( pixmap );
// render image into pixmap
imlib_render_image_on_drawable_at_size( 0, 0, width, height );
// set pixmap as background
XSetWindowBackgroundPixmap( display, root, pixmap );
// clear window
XClearWindow( display, root );
XFlush( display );
// free...
XFreePixmap( display, pixmap );
imlib_context_set_image( img );
imlib_free_image();
imlib_context_set_image( img2 );
imlib_free_image();
// close display
XCloseDisplay( display );
return 0;
}
It's changing wallpaper, but I want to blend this two images with custom alpha, I mean, something like this: How to blend two image
So, how to set image transparency for blending operation in Imlib?
Compile with: gcc main.c -lX11 -lImlib2

Answer 1

Ok, I got it!
First I need to set alpha for image, create second imlib object and fill with rectangle in custom color with alpha. Then just copy alpha from one image to second... That's just... ehh...
imlib_context_set_image( img );
w1 = imlib_image_get_width();
h1 = imlib_image_get_height();
img3 = imlib_create_image( w1, h1 );
imlib_context_set_image( img3 );
imlib_image_set_has_alpha( 1 );
imlib_context_set_color( 0, 0, 0, 150 );
imlib_image_fill_rectangle( 0, 0, w1, h1 );
imlib_context_set_image( img );
imlib_image_set_has_alpha( 1 );
imlib_image_copy_alpha_to_image( img3, 0, 0 );
imlib_context_set_image( img2 );
imlib_context_set_operation( IMLIB_OP_COPY );
imlib_blend_image_onto_image( img, 1, 0, 0, w1, h1, 0, 0, w1, h1 );
Here img and img2 variables are pictures. It gives image blended onto image with given in imlib_context_set_color alpha.