VampireSurvivors/src/system/frame.zig

const std = @import("std");
const sdl = @import("sdl");
const App = @import("app");

const component = @import("../component/root.zig");
const resource = @import("../resource/root.zig");

/// ----------------------------------------------------
/// ----------------------------------------------------
pub fn beginFrame(ctx: App.scheduler.Context) !void {
    const res = try ctx.app.resources.getMany(struct {
        window: *resource.Window,
        frame: *resource.Frame,
        time: *resource.Time,
    });

    //
    // TIME
    //

    res.time.last = res.time.now;
    res.time.now = sdl.SDL_GetPerformanceCounter();

    res.time.dt =
        @as(f32, @floatFromInt(res.time.now - res.time.last)) /
        @as(f32, @floatFromInt(res.time.frequency));

    //
    // CAMERA
    //

    var target_transform: ?*const component.Transform = null;

    { // GATHER CAMERAS TARGET
        var query = ctx.app.world.query(struct {
            transform: *component.Transform,
            camera_target: ?*component.CameraTarget,
        }, .{});
        while (query.next()) |e| {
            if (e.camera_target) |_| {
                target_transform = e.transform;
            }
        }
    }

    { // GATHER CAMERAS
        var query = ctx.app.world.query(struct {
            camera: *component.Camera,
            transform: *component.Transform,
        }, .{});
        while (query.next()) |e| {
            const window_width: f32 = @floatFromInt(res.window.width);
            const window_height: f32 = @floatFromInt(res.window.height);
            const target = if (target_transform) |v| v else continue;

            e.transform.pos[0] += ((window_width / 2.0) - (target.pos[0] + target.size[0] / 2.0) - e.transform.pos[0]) / 20.0;
            e.transform.pos[1] += ((window_height / 2.0) - (target.pos[1] + target.size[1] / 2.0) - e.transform.pos[1]) / 20.0;

            // --- SET CURRENT FRAME CAMERA ---
            res.frame.camera = .{
                .value = e.camera,
                .transform = e.transform,
            };
        }
    }
}

/// ----------------------------------------------------
/// ----------------------------------------------------
pub fn endFrame(ctx: App.scheduler.Context) !void {
    const res = try ctx.app.resources.getMany(struct {
        frame: *resource.Frame,
        time: *resource.Time,
    });

    res.frame.camera = null;

    const frame_time =
        @as(f32, @floatFromInt(sdl.SDL_GetPerformanceCounter() - res.time.now)) /
        @as(f32, @floatFromInt(res.time.frequency));

    if (frame_time < res.time.target_dt) {
        const delay_ms = (res.time.target_dt - frame_time) * 1000.0;
        sdl.SDL_Delay(@intFromFloat(delay_ms));
    }
}

/// ----------------------------------------------------
/// ----------------------------------------------------
pub fn updateTransforms(ctx: App.scheduler.Context) !void {
    const res = try ctx.app.resources.getMany(struct {
        time: *resource.Time,
    });

    // --- QUERY ---
    var query = ctx.app.world.query(struct {
        transform: *component.Transform,
        velocity: *component.Velocity,
        friction: ?*component.Friction,
    }, .{});
    while (query.next()) |e| {
        // --- APPLY VELOCITY ---
        e.transform.pos[0] += e.velocity.value[0] * res.time.dt;
        e.transform.pos[1] += e.velocity.value[1] * res.time.dt;

        // --- APPLY FRICTION ---
        if (e.friction) |friction| {
            const damping = std.math.exp(-friction.value * res.time.dt);
            e.velocity.value[0] *= damping;
            e.velocity.value[1] *= damping;
        }
    }
}

/// ----------------------------------------------------
/// ----------------------------------------------------
pub fn updateTimers(ctx: App.scheduler.Context) !void {
    const res = try ctx.app.resources.getMany(struct {
        time: *resource.Time,
    });

    var query = ctx.app.world.query(struct {
        timer: *component.Timer,
    }, .{});
    while (query.next()) |e| {
        // --- # ---
        if (e.timer.finished and !e.timer.repeat)
            continue;

        // --- PROGRESS ---
        e.timer.remaining -=
            res.time.dt;

        if (e.timer.remaining <= 0.0) {
            e.timer.finished = true;

            if (e.timer.repeat) {
                e.timer.remaining = e.timer.duration;
                e.timer.finished = false;
            }
        }
    }
}

/// ----------------------------------------------------
/// ----------------------------------------------------
pub fn cast(ctx: App.scheduler.Context) !void {
    const res = try ctx.app.resources.getMany(struct {
        time: *resource.Time,
    });

    // --- QUERY ---
    var query = ctx.app.world.query(struct {
        caster: *component.Caster,
        transform: *component.Transform,
    }, .{});
    while (query.next()) |e| {
        // --- SUBTRACT COOLDOWN ---
        e.caster.current_cooldown -=
            @max(0, res.time.dt);

        // --- SKIP IF ON COOLDOWN ---
        if (e.caster.current_cooldown >= 0)
            continue;

        // --- SPAWN PROJECTILE ---
        try ctx.app.world.spawn(.{
            component.Transform{
                .pos = e.transform.pos,
            },
            component.Velocity{
                .value = .{ 400, 0 },
            },
            component.Material{
                .style = .{ .solid = .{ 200, 20, 20, 255 } },
            },
            component.Projectile{},
        });

        // --- SET COOLDOWN ---
        e.caster.current_cooldown =
            e.caster.cooldown;
    }
}