text: #define _POSIX_C_SOURCE 200112L
  #include <drm_fourcc.h>
  #include <limits.h>
  #include <math.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <strings.h>
  #include <time.h>
  #include <unistd.h>
  #include <wayland-server-core.h>
  #include <wlr/backend.h>
  #include <wlr/backend/session.h>
  #include <wlr/render/wlr_renderer.h>
  #include <wlr/types/wlr_keyboard.h>
  #include <wlr/types/wlr_matrix.h>
  #include <wlr/types/wlr_input_device.h>
  #include <wlr/types/wlr_output_layout.h>
  #include <wlr/types/wlr_output.h>
  #include <wlr/util/box.h>
  #include <wlr/util/log.h>
  #include <xkbcommon/xkbcommon.h>
  #include "cat.h"
  
  struct sample_state {
  	struct wl_display *display;
  	struct wl_listener new_output;
  	struct wl_listener new_input;
  	struct wlr_renderer *renderer;
  	struct wlr_texture *cat_texture;
  	struct wlr_output_layout *layout;
  	float x_offs, y_offs;
  	float x_vel, y_vel;
  	struct timespec ts_last;
  };
  
  struct sample_output {
  	struct sample_state *sample;
  	struct wlr_output *output;
  	struct wl_listener frame;
  	struct wl_listener destroy;
  };
  
  struct sample_keyboard {
  	struct sample_state *sample;
  	struct wlr_input_device *device;
  	struct wl_listener key;
  	struct wl_listener destroy;
  };
  
  static void animate_cat(struct sample_state *sample,
  		struct wlr_output *output) {
  	struct timespec ts;
  	clock_gettime(CLOCK_MONOTONIC, &ts);
  	long ms = (ts.tv_sec - sample->ts_last.tv_sec) * 1000 +
  		(ts.tv_nsec - sample->ts_last.tv_nsec) / 1000000;
  	// how many seconds have passed since the last time we animated
  	float seconds = ms / 1000.0f;
  
  	if (seconds > 0.1f) {
  		// XXX when we switch vt, the rendering loop stops so try to detect
  		// that and pause when it happens.
  		seconds = 0.0f;
  	}
  
  	// check for collisions and bounce
  	bool ur_collision = !wlr_output_layout_output_at(sample->layout,
  			sample->x_offs + 128, sample->y_offs);
  	bool ul_collision = !wlr_output_layout_output_at(sample->layout,
  			sample->x_offs, sample->y_offs);
  	bool ll_collision = !wlr_output_layout_output_at(sample->layout,
  			sample->x_offs, sample->y_offs + 128);
  	bool lr_collision = !wlr_output_layout_output_at(sample->layout,
  			sample->x_offs + 128, sample->y_offs + 128);
  
  	if (ur_collision && ul_collision && ll_collision && lr_collision) {
  		// oops we went off the screen somehow
  		struct wlr_output_layout_output *l_output =
  			wlr_output_layout_get(sample->layout, output);
  		sample->x_offs = l_output->x + 20;
  		sample->y_offs = l_output->y + 20;
  	} else if (ur_collision && ul_collision) {
  		sample->y_vel = fabs(sample->y_vel);
  	} else if (lr_collision && ll_collision) {
  		sample->y_vel = -fabs(sample->y_vel);
  	} else if (ll_collision && ul_collision) {
  		sample->x_vel = fabs(sample->x_vel);
  	} else if (ur_collision && lr_collision) {
  		sample->x_vel = -fabs(sample->x_vel);
  	} else {
  		if (ur_collision || lr_collision) {
  			sample->x_vel = -fabs(sample->x_vel);
  		}
  		if (ul_collision || ll_collision) {
  			sample->x_vel = fabs(sample->x_vel);
  		}
  		if (ul_collision || ur_collision) {
  			sample->y_vel = fabs(sample->y_vel);
  		}
  		if (ll_collision || lr_collision) {
  			sample->y_vel = -fabs(sample->y_vel);
  		}
  	}
  
  	sample->x_offs += sample->x_vel * seconds;
  	sample->y_offs += sample->y_vel * seconds;
  	sample->ts_last = ts;
  }
  
  static void output_frame_notify(struct wl_listener *listener, void *data) {
  	struct sample_output *output = wl_container_of(listener, output, frame);
  	struct sample_state *sample = output->sample;
  	struct timespec ts;
  	clock_gettime(CLOCK_MONOTONIC, &ts);
  
  	struct wlr_output *wlr_output = output->output;
  
  	wlr_output_attach_render(wlr_output, NULL);
  	wlr_renderer_begin(sample->renderer, wlr_output->width, wlr_output->height);
  	wlr_renderer_clear(sample->renderer, (float[]){0.25f, 0.25f, 0.25f, 1});
  
  	animate_cat(sample, output->output);
  
  	struct wlr_box box = {
  		.x = sample->x_offs, .y = sample->y_offs,
  		.width = 128, .height = 128,
  	};
  	if (wlr_output_layout_intersects(sample->layout, output->output, &box)) {
  		// transform global coordinates to local coordinates
  		double local_x = sample->x_offs;
  		double local_y = sample->y_offs;
  		wlr_output_layout_output_coords(sample->layout, output->output,
  			&local_x, &local_y);
  
  		wlr_render_texture(sample->renderer, sample->cat_texture,
  			wlr_output->transform_matrix, local_x, local_y, 1.0f);
  	}
  
  	wlr_renderer_end(sample->renderer);
  	wlr_output_commit(wlr_output);
  }
  
  static void update_velocities(struct sample_state *sample,
  		float x_diff, float y_diff) {
  	sample->x_vel += x_diff;
  	sample->y_vel += y_diff;
  }
  
  static void output_remove_notify(struct wl_listener *listener, void *data) {
  	struct sample_output *sample_output = wl_container_of(listener, sample_output, destroy);
  	struct sample_state *sample = sample_output->sample;
  	wlr_output_layout_remove(sample->layout, sample_output->output);
  	wl_list_remove(&sample_output->frame.link);
  	wl_list_remove(&sample_output->destroy.link);
  	free(sample_output);
  }
  
  static void new_output_notify(struct wl_listener *listener, void *data) {
  	struct wlr_output *output = data;
  	struct sample_state *sample = wl_container_of(listener, sample, new_output);
  	struct sample_output *sample_output = calloc(1, sizeof(struct sample_output));
  	wlr_output_layout_add_auto(sample->layout, output);
  	sample_output->output = output;
  	sample_output->sample = sample;
  	wl_signal_add(&output->events.frame, &sample_output->frame);
  	sample_output->frame.notify = output_frame_notify;
  	wl_signal_add(&output->events.destroy, &sample_output->destroy);
  	sample_output->destroy.notify = output_remove_notify;
  
  	struct wlr_output_mode *mode = wlr_output_preferred_mode(output);
  	if (mode != NULL) {
  		wlr_output_set_mode(output, mode);
  	}
  
  	wlr_output_commit(output);
  }
  
  static void keyboard_key_notify(struct wl_listener *listener, void *data) {
  	struct sample_keyboard *keyboard = wl_container_of(listener, keyboard, key);
  	struct sample_state *sample = keyboard->sample;
  	struct wlr_event_keyboard_key *event = data;
  	uint32_t keycode = event->keycode + 8;
  	const xkb_keysym_t *syms;
  	int nsyms = xkb_state_key_get_syms(keyboard->device->keyboard->xkb_state,
  			keycode, &syms);
  	for (int i = 0; i < nsyms; i++) {
  		xkb_keysym_t sym = syms[i];
  		if (sym == XKB_KEY_Escape) {
  			wl_display_terminate(sample->display);
  		}
  		// NOTE: It may be better to simply refer to our key state during each frame
  		// and make this change in pixels/sec^2
  		// Also, key repeat
  		int delta = 75;
  		if (event->state == WL_KEYBOARD_KEY_STATE_PRESSED) {
  			switch (sym) {
  			case XKB_KEY_Left:
  				update_velocities(sample, -delta, 0);
  				break;
  			case XKB_KEY_Right:
  				update_velocities(sample, delta, 0);
  				break;
  			case XKB_KEY_Up:
  				update_velocities(sample, 0, -delta);
  				break;
  			case XKB_KEY_Down:
  				update_velocities(sample, 0, delta);
  				break;
  			}
  		}
  	}
  }
  
  static void keyboard_destroy_notify(struct wl_listener *listener, void *data) {
  	struct sample_keyboard *keyboard = wl_container_of(listener, keyboard, destroy);
  	wl_list_remove(&keyboard->destroy.link);
  	wl_list_remove(&keyboard->key.link);
  	free(keyboard);
  }
  
  static void new_input_notify(struct wl_listener *listener, void *data) {
  	struct wlr_input_device *device = data;
  	struct sample_state *sample = wl_container_of(listener, sample, new_input);
  	switch (device->type) {
  	case WLR_INPUT_DEVICE_KEYBOARD:;
  		struct sample_keyboard *keyboard = calloc(1, sizeof(struct sample_keyboard));
  		keyboard->device = device;
  		keyboard->sample = sample;
  		wl_signal_add(&device->events.destroy, &keyboard->destroy);
  		keyboard->destroy.notify = keyboard_destroy_notify;
  		wl_signal_add(&device->keyboard->events.key, &keyboard->key);
  		keyboard->key.notify = keyboard_key_notify;
  		struct xkb_context *context = xkb_context_new(XKB_CONTEXT_NO_FLAGS);
  		if (!context) {
  			wlr_log(WLR_ERROR, "Failed to create XKB context");
  			exit(1);
  		}
  		struct xkb_keymap *keymap = xkb_keymap_new_from_names(context, NULL,
  			XKB_KEYMAP_COMPILE_NO_FLAGS);
  		if (!keymap) {
  			wlr_log(WLR_ERROR, "Failed to create XKB keymap");
  			exit(1);
  		}
  		wlr_keyboard_set_keymap(device->keyboard, keymap);
  		xkb_keymap_unref(keymap);
  		xkb_context_unref(context);
  		break;
  	default:
  		break;
  	}
  }
  
  
  int main(int argc, char *argv[]) {
  	wlr_log_init(WLR_DEBUG, NULL);
  	struct wl_display *display = wl_display_create();
  	struct sample_state state = {
  		.x_vel = 500,
  		.y_vel = 500,
  		.display = display,
  	};
  
  	state.layout = wlr_output_layout_create();
  	clock_gettime(CLOCK_MONOTONIC, &state.ts_last);
  
  	struct wlr_backend *wlr = wlr_backend_autocreate(display);
  	if (!wlr) {
  		exit(1);
  	}
  
  	wl_signal_add(&wlr->events.new_output, &state.new_output);
  	state.new_output.notify = new_output_notify;
  	wl_signal_add(&wlr->events.new_input, &state.new_input);
  	state.new_input.notify = new_input_notify;
  
  	state.renderer = wlr_backend_get_renderer(wlr);
  	state.cat_texture = wlr_texture_from_pixels(state.renderer,
  		DRM_FORMAT_ABGR8888, cat_tex.width * 4, cat_tex.width, cat_tex.height,
  		cat_tex.pixel_data);
  
  	if (!wlr_backend_start(wlr)) {
  		wlr_log(WLR_ERROR, "Failed to start backend");
  		wlr_backend_destroy(wlr);
  		exit(1);
  	}
  	wl_display_run(display);
  
  	wlr_texture_destroy(state.cat_texture);
  
  	wl_display_destroy(state.display);
  	wlr_output_layout_destroy(state.layout);
  }
  