//! The display wire protocol — what a client says to the display service over its
//! well-known `.display` endpoint. extern-struct messages with an `Operation` tag, the
//! same shape as block/vfs/input protocols. The compositor owns the framebuffer and an
//! ordered stack of **layers**; a client creates layers, draws into them with these
//! operations, marks damage, and asks for a `present`. v1 surfaces are server-owned (a
//! client draws by command); shared-memory surfaces are a later milestone (docs/display.md).

pub const Operation = enum(u32) {
    /// info() -> { width, height, pitch, format }: the display's current mode.
    info = 0,
    /// create_layer(x, y, width, height, z) -> { layer }: a new server-owned surface.
    create_layer = 1,
    /// configure_layer(layer, x, y, z, visible): move, restack, show, or hide a layer.
    configure_layer = 2,
    /// destroy_layer(layer): release a layer.
    destroy_layer = 3,
    /// fill_rect(layer, x, y, width, height, colour): fill a rectangle of a layer.
    fill_rect = 4,
    /// blit_tile(layer, x, y, width, height, <inline pixels>): copy a small pixel tile in.
    blit_tile = 5,
    /// damage(layer, x, y, width, height): mark a region dirty for the next present.
    damage = 6,
    /// present(): composite the dirty layers and flush to the screen.
    present = 7,
};

/// The fixed request header. A `blit_tile`'s pixel payload (width*height 32-bit pixels)
/// follows this header inline in the same message, up to `maximum_payload`.
pub const Request = extern struct {
    operation: u32,
    layer: u32 = 0, // create/configure/destroy/fill/blit/damage: the target layer
    x: u32 = 0,
    y: u32 = 0,
    width: u32 = 0,
    height: u32 = 0,
    z: u32 = 0, // create_layer / configure_layer: stacking order (higher = in front)
    colour: u32 = 0, // fill_rect: the fill colour (native pixel value)
    visible: u32 = 1, // configure_layer: 0 hides the layer
    reserved: u32 = 0,
};

pub const Reply = extern struct {
    status: i32, // 0 on success, negative on failure
    reserved: u32 = 0,
    // info():
    width: u32 = 0,
    height: u32 = 0,
    pitch: u32 = 0,
    format: u32 = 0, // a device-abi DisplayFormat value (0 = rgbx, 1 = bgrx)
    // create_layer():
    layer: u32 = 0,
    reserved2: u32 = 0,
};

/// Sized to hold a modest `blit_tile` payload (a cursor / glyph-cell tile) inline on top
/// of the header, not just the fixed messages — the compositor's receive/reply buffers
/// (`runtime.service.run`) are this big.
pub const message_maximum: usize = 4096;
pub const request_size: usize = @sizeOf(Request);
pub const reply_size: usize = @sizeOf(Reply);
pub const maximum_payload: usize = message_maximum - request_size;