RTSP-Streamer/internal/compositor/compositor.go

// Package compositor drives a running sway session to tile mpv windows into a
// grid. The daemon does NOT launch sway; the standard kiosk pattern is for
// sway (started at boot via autologin) to exec the daemon, so SWAYSOCK and
// WAYLAND_DISPLAY are inherited. This package shells out to swaymsg, which is
// always present alongside sway and speaks the sway IPC for us.
package compositor

import (
	"context"
	"encoding/json"
	"fmt"
	"os/exec"
)

// Rect is a pixel rectangle on the output. The JSON tags match sway's
// get_tree/get_outputs "rect" objects so it can be decoded directly.
type Rect struct {
	X int `json:"x"`
	Y int `json:"y"`
	W int `json:"width"`
	H int `json:"height"`
}

// GridRects splits a WxH area into cols*rows cells in row-major order. The
// final column and row absorb any rounding remainder so there are no gaps.
func GridRects(width, height, cols, rows int) []Rect {
	rects := make([]Rect, 0, cols*rows)
	for r := 0; r < rows; r++ {
		for c := 0; c < cols; c++ {
			x := c * width / cols
			y := r * height / rows
			// Right/bottom edge computed from the next cell boundary to avoid
			// cumulative rounding gaps.
			x2 := (c + 1) * width / cols
			y2 := (r + 1) * height / rows
			if c == cols-1 {
				x2 = width
			}
			if r == rows-1 {
				y2 = height
			}
			rects = append(rects, Rect{X: x, Y: y, W: x2 - x, H: y2 - y})
		}
	}
	return rects
}

// TileRect computes the pixel rectangle for a tile spanning (colspan x rowspan)
// cells starting at (col,row) in a cols x rows base grid over a WxH output.
// Boundaries are computed from cell edges so adjacent tiles meet exactly and
// the far edges reach the full width/height with no rounding gaps.
func TileRect(width, height, cols, rows, col, row, colspan, rowspan int) Rect {
	x := col * width / cols
	y := row * height / rows
	x2 := (col + colspan) * width / cols
	y2 := (row + rowspan) * height / rows
	if col+colspan >= cols {
		x2 = width
	}
	if row+rowspan >= rows {
		y2 = height
	}
	return Rect{X: x, Y: y, W: x2 - x, H: y2 - y}
}

// Client talks to sway via swaymsg.
type Client struct {
	bin string
}

// New returns a compositor client. It verifies swaymsg is on PATH.
func New() (*Client, error) {
	bin, err := exec.LookPath("swaymsg")
	if err != nil {
		return nil, fmt.Errorf("swaymsg not found on PATH: %w", err)
	}
	return &Client{bin: bin}, nil
}

// run executes a raw sway command string.
func (c *Client) run(ctx context.Context, command string) error {
	out, err := exec.CommandContext(ctx, c.bin, command).CombinedOutput()
	if err != nil {
		return fmt.Errorf("swaymsg %q: %w: %s", command, err, out)
	}
	return nil
}

// Output describes a connected display from `swaymsg -t get_outputs`.
type Output struct {
	Name        string `json:"name"`
	Active      bool   `json:"active"`
	Focused     bool   `json:"focused"`
	CurrentMode struct {
		Width  int `json:"width"`
		Height int `json:"height"`
	} `json:"current_mode"`
	Rect Rect `json:"-"`
}

// PrimaryOutput returns the focused active output (or the first active one),
// used to auto-detect resolution when the config doesn't pin it.
func (c *Client) PrimaryOutput(ctx context.Context) (*Output, error) {
	out, err := exec.CommandContext(ctx, c.bin, "-t", "get_outputs", "-r").Output()
	if err != nil {
		return nil, fmt.Errorf("get_outputs: %w", err)
	}
	var outputs []Output
	if err := json.Unmarshal(out, &outputs); err != nil {
		return nil, err
	}
	var first *Output
	for i := range outputs {
		o := &outputs[i]
		if !o.Active {
			continue
		}
		if first == nil {
			first = o
		}
		if o.Focused {
			return o, nil
		}
	}
	if first == nil {
		return nil, fmt.Errorf("no active output found")
	}
	return first, nil
}

// treeNode is the recursive shape of `swaymsg -t get_tree`.
type treeNode struct {
	PID   int        `json:"pid"`
	Name  string     `json:"name"`
	AppID string     `json:"app_id"`
	Rect  Rect       `json:"rect"`
	Nodes []treeNode `json:"nodes"`
	Float []treeNode `json:"floating_nodes"`
}

func (n *treeNode) walk(fn func(*treeNode)) {
	fn(n)
	for i := range n.Nodes {
		n.Nodes[i].walk(fn)
	}
	for i := range n.Float {
		n.Float[i].walk(fn)
	}
}

// WindowRects returns the geometry of every mapped window keyed by owning
// pid, from a single get_tree round trip. The daemon checks all tiles against
// one snapshot instead of issuing a swaymsg per window.
func (c *Client) WindowRects(ctx context.Context) (map[int]Rect, error) {
	out, err := exec.CommandContext(ctx, c.bin, "-t", "get_tree", "-r").Output()
	if err != nil {
		return nil, fmt.Errorf("get_tree: %w", err)
	}
	var root treeNode
	if err := json.Unmarshal(out, &root); err != nil {
		return nil, err
	}
	rects := map[int]Rect{}
	root.walk(func(n *treeNode) {
		if n.PID != 0 && (n.AppID != "" || n.Name != "") {
			rects[n.PID] = n.Rect
		}
	})
	return rects, nil
}

// Place floats and positions the window owned by pid at the given rect. Using
// the pid criterion means we never depend on window titles or app-ids.
func (c *Client) Place(ctx context.Context, pid int, r Rect) error {
	cmd := fmt.Sprintf(
		"[pid=%d] floating enable, border none, move absolute position %d %d, resize set %d %d",
		pid, r.X, r.Y, r.W, r.H,
	)
	return c.run(ctx, cmd)
}

// PrepareForMPV installs global rules so every mpv window is borderless and
// floating the moment it maps, avoiding a flash of tiled/bordered video before
// Place runs. Safe to call repeatedly.
func (c *Client) PrepareForMPV(ctx context.Context) error {
	return c.run(ctx, `for_window [app_id="mpv"] floating enable, border none`)
}

// PlaceOnMap installs a for_window rule that positions any window with the
// given title at rect the moment it maps. This is what keeps a restarting
// stream from flashing at the wrong place/size: sway applies the geometry
// synchronously at map time, before the daemon's corrective loop ever sees
// the window. Re-installing a rule for the same title replaces it. The title
// is anchored (^...$) so slot-1 never matches slot-10.
func (c *Client) PlaceOnMap(ctx context.Context, title string, r Rect) error {
	cmd := fmt.Sprintf(
		`for_window [title="^%s$"] floating enable, border none, move absolute position %d %d, resize set %d %d`,
		title, r.X, r.Y, r.W, r.H,
	)
	return c.run(ctx, cmd)
}