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# Contributing to sway
Contributing just involves sending a pull request. You will probably be more
successful with your contribution if you visit the [IRC
channel](http://webchat.freenode.net/?channels=sway&uio=d4) upfront and discuss
your plans.
## Pull Requests
If you already have your own pull request habits, feel free to use them. If you
don't, however, allow me to make a suggestion: feature branches pulled from
upstream. Try this:
1. Fork sway
2. Clone your fork
3. git remote add upstream git://github.com/SirCmpwn/sway.git
You only need to do this once. You're never going to use your fork's master
branch. Instead, when you start working on a feature, do this:
1. git fetch upstream
2. git checkout -b add-so-and-so-feature upstream/master
3. work
4. git push -u origin add-so-and-so-feature
5. Make pull request from your feature branch
## Coding Style
Sway is written in C. The style guidelines is [kernel
style](https://www.kernel.org/doc/Documentation/CodingStyle), but all braces go
on the same line (*"but K&R says so!" is a silly way of justifying something*).
Some points to note:
* Do not use typedefs unless you have a good reason
* Do not use macros unless you have a *really* good reason
* Align `case` with `switch`
* Tabs, not spaces
* `char *pointer` - note position of `*`
* Use logging with reckless abandon
* Always include braces for if/for/while/etc, even for one-liners
An example of well formatted code:
```C
#include <stdio.h>
#include <stdlib.h>
#include "log.h"
#include "example.h"
struct foobar {
char *foo;
int bar;
long baz;
}; // Do not typedef without a good reason
int main(int argc, const char **argv) {
if (argc != 4) {
sway_abort("Do not run this program manually. See man 5 sway and look for output options.");
}
if (!registry->desktop_shell) {
sway_abort("swaybg requires the compositor to support the desktop-shell extension.");
}
int desired_output = atoi(argv[1]);
sway_log(L_INFO, "Using output %d of %d", desired_output, registry->outputs->length);
int i;
struct output_state *output = registry->outputs->items[desired_output];
struct window *window = window_setup(registry, 100, 100, false);
if (!window) {
sway_abort("Failed to create surfaces.");
}
window->width = output->width;
window->height = output->height;
desktop_shell_set_background(registry->desktop_shell, output->output, window->surface);
list_add(surfaces, window);
cairo_surface_t *image = cairo_image_surface_create_from_png(argv[2]);
double width = cairo_image_surface_get_width(image);
double height = cairo_image_surface_get_height(image);
const char *scaling_mode_str = argv[3];
enum scaling_mode scaling_mode;
if (strcmp(scaling_mode_str, "stretch") == 0) {
scaling_mode = SCALING_MODE_STRETCH;
} else if (strcmp(scaling_mode_str, "fill") == 0) {
scaling_mode = SCALING_MODE_FILL;
} else if (strcmp(scaling_mode_str, "fit") == 0) {
scaling_mode = SCALING_MODE_FIT;
} else if (strcmp(scaling_mode_str, "center") == 0) {
scaling_mode = SCALING_MODE_CENTER;
} else if (strcmp(scaling_mode_str, "tile") == 0) {
scaling_mode = SCALING_MODE_TILE;
} else {
sway_abort("Unsupported scaling mode: %s", scaling_mode_str);
}
for (i = 0; i < surfaces->length; ++i) {
struct window *window = surfaces->items[i];
if (window_prerender(window) && window->cairo) {
switch (scaling_mode) {
case SCALING_MODE_STRETCH:
cairo_scale(window->cairo,
(double) window->width / width,
(double) window->height / height);
cairo_set_source_surface(window->cairo, image, 0, 0);
break;
case SCALING_MODE_FILL:
{
double window_ratio = (double) window->width / window->height;
double bg_ratio = width / height;
if (window_ratio > bg_ratio) {
double scale = (double) window->width / width;
cairo_scale(window->cairo, scale, scale);
cairo_set_source_surface(window->cairo, image,
0,
(double) window->height/2 / scale - height/2);
} else {
double scale = (double) window->height / height;
cairo_scale(window->cairo, scale, scale);
cairo_set_source_surface(window->cairo, image,
(double) window->width/2 / scale - width/2,
0);
}
}
break;
case SCALING_MODE_FIT:
{
double window_ratio = (double) window->width / window->height;
double bg_ratio = width / height;
if (window_ratio > bg_ratio) {
double scale = (double) window->height / height;
cairo_scale(window->cairo, scale, scale);
cairo_set_source_surface(window->cairo, image,
(double) window->width/2 / scale - width/2,
0);
} else {
double scale = (double) window->width / width;
cairo_scale(window->cairo, scale, scale);
cairo_set_source_surface(window->cairo, image,
0,
(double) window->height/2 / scale - height/2);
}
}
break;
case SCALING_MODE_CENTER:
cairo_set_source_surface(window->cairo, image,
(double) window->width/2 - width/2,
(double) window->height/2 - height/2);
break;
case SCALING_MODE_TILE:
{
cairo_pattern_t *pattern = cairo_pattern_create_for_surface(image);
cairo_pattern_set_extend(pattern, CAIRO_EXTEND_REPEAT);
cairo_set_source(window->cairo, pattern);
}
break;
default:
sway_abort("Scaling mode '%s' not implemented yet!", scaling_mode_str);
}
cairo_paint(window->cairo);
window_render(window);
}
}
while (wl_display_dispatch(registry->display) != -1);
for (i = 0; i < surfaces->length; ++i) {
struct window *window = surfaces->items[i];
window_teardown(window);
}
list_free(surfaces);
registry_teardown(registry);
return 0;
}
```