//! system/services/display-demo — a hardware-free client of the display service, the
//! `input-source` analog for the compositor. It creates a wallpaper and a rectangle it
//! slides each frame, then drives the compositor in a present loop — proof that a
//! *separate process* can compose a moving scene through the display service over IPC,
//! exercising the layer client API and damage-driven present end to end
//! (docs/display.md). It logs `display-demo: ok` once it has driven a run of frames.
//!
//! It draws no cursor and reads no input: the on-screen cursor is the display service's
//! own, tracked by the service's mouse-listener thread (docs/display.md). The demo's job
//! is only to prove client-driven animation, so its loop runs on its own frame timer and
//! is deliberately independent of the mouse.

const runtime = @import("runtime");
const display = runtime.display;
const system = runtime.system;
const time = runtime.time;

pub fn main() void {
    const mode = display.info() orelse {
        _ = system.write("display-demo: no display service\n");
        return;
    };

    // A full-screen wallpaper under everything.
    const wallpaper = display.createLayer(0, 0, mode.width, mode.height, 0) orelse return createFailed();
    _ = wallpaper.fill(0, 0, mode.width, mode.height, display.color(0x10, 0x18, 0x28));

    // A rectangle that slides back and forth.
    const box_w: u32 = 140;
    const box_h: u32 = 100;
    const box_y: i32 = 200;
    const box = display.createLayer(0, box_y, box_w, box_h, 1) orelse return createFailed();
    _ = box.fill(0, 0, box_w, box_h, display.color(0xE0, 0x60, 0x40));

    _ = display.present();
    _ = system.write("display-demo: scene up; animating\n");

    const span: i32 = @as(i32, @intCast(mode.width)) - @as(i32, @intCast(box_w));
    var x: i32 = 0;
    var dx: i32 = 8;
    var frame: u32 = 0;

    while (true) : (frame += 1) {
        x += dx;
        if (x <= 0) {
            x = 0;
            dx = -dx;
        } else if (x >= span) {
            x = span;
            dx = -dx;
        }
        _ = box.configure(x, box_y, 1, true); // move it; the compositor repaints old + new
        _ = display.present();
        // A run of frames drawn through the compositor is the automated proof (the visible
        // motion is a screenshot away via `zig build run-x86-64`).
        if (frame == 20) _ = system.write("display-demo: ok\n");
        time.sleep(time.Duration.fromMillis(30));
    }
}

fn createFailed() void {
    _ = system.write("display-demo: create failed\n");
}