convince/CONTRIBUTING.md

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 upfront and discuss your plans.

Coding Style

Sway is written in C. The style guidelines is kernel style, 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:

#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;
}