feat: activating and undoing actions

Added `tile_offset` and `tile_stride` to render exactly the card without
the blank space surrounding it on the tile.

src/assets.zig

@@ -0,0 +1,301 @@
+pub const Suit = enum(u2) {
+    clubs = 0b00,
+    spades = 0b01,
+    hearts = 0b10,
+    diamonds = 0b11,
+
+    pub fn color(this: @This()) u1 {
+        return (@intFromEnum(this) & 0b10) >> 1;
+    }
+};
+
+pub const Card = packed struct(u6) {
+    suit: Suit,
+    rank: u4,
+};
+
+/// A texture with a regular grid of sprites
+pub const TileSheet = struct {
+    texture: seizer.Texture,
+    tile_offset: [2]u32,
+    tile_size: [2]u32,
+    tile_stride: [2]u32,
+
+    pub const InitOptions = struct {
+        allocator: std.mem.Allocator,
+        image_file_contents: []const u8,
+        tile_offset: [2]u32,
+        tile_size: [2]u32,
+        tile_stride: [2]u32,
+        texture_options: seizer.Texture.InitFromFileOptions = .{},
+    };
+
+    pub fn init(options: InitOptions) !@This() {
+        const texture = try seizer.Texture.initFromFileContents(
+            options.allocator,
+            options.image_file_contents,
+            options.texture_options,
+        );
+        return @This(){
+            .texture = texture,
+            .tile_offset = options.tile_offset,
+            .tile_size = options.tile_size,
+            .tile_stride = options.tile_stride,
+        };
+    }
+
+    pub fn deinit(this: *@This()) void {
+        this.texture.deinit();
+    }
+
+    pub fn renderTile(this: @This(), canvas: *seizer.Canvas, tile_id: u32, pos: [2]f32, options: struct {
+        size: ?[2]f32 = null,
+    }) void {
+        const texture_sizef = [2]f32{
+            @floatFromInt(this.texture.size[0]),
+            @floatFromInt(this.texture.size[1]),
+        };
+        const tile_offsetf = [2]f32{
+            @floatFromInt(this.tile_offset[0]),
+            @floatFromInt(this.tile_offset[1]),
+        };
+        const tile_stridef = [2]f32{
+            @floatFromInt(this.tile_stride[0]),
+            @floatFromInt(this.tile_stride[1]),
+        };
+        const tile_sizef = [2]f32{
+            @floatFromInt(this.tile_size[0]),
+            @floatFromInt(this.tile_size[1]),
+        };
+        // add a half to round up
+        const size_in_tiles = [2]u32{
+            (@as(u32, @intCast(this.texture.size[0])) + (this.tile_stride[0] / 2)) / this.tile_stride[0],
+            (@as(u32, @intCast(this.texture.size[1])) + (this.tile_stride[1] / 2)) / this.tile_stride[1],
+        };
+        const pos_in_tiles = [2]u32{
+            tile_id % size_in_tiles[0],
+            tile_id / size_in_tiles[0],
+        };
+        const pos_in_tilesf = [2]f32{
+            @floatFromInt(pos_in_tiles[0]),
+            @floatFromInt(pos_in_tiles[1]),
+        };
+
+        const pixel_pos = [2]f32{
+            pos_in_tilesf[0] * tile_stridef[0] + tile_offsetf[0],
+            pos_in_tilesf[1] * tile_stridef[1] + tile_offsetf[1],
+        };
+        const uv = seizer.geometry.AABB(f32){
+            .min = .{
+                pixel_pos[0] / texture_sizef[0],
+                pixel_pos[1] / texture_sizef[1],
+            },
+            .max = .{
+                (pixel_pos[0] + tile_sizef[0]) / texture_sizef[0],
+                (pixel_pos[1] + tile_sizef[1]) / texture_sizef[1],
+            },
+        };
+
+        canvas.rect(pos, options.size orelse tile_sizef, .{
+            .texture = this.texture.glTexture,
+            .uv = uv,
+        });
+    }
+};
+
+/// A texture with a regular grid of sprites
+pub const DeckSprites = struct {
+    tilesheet: TileSheet,
+    /// Return the tile index for a given card,
+    mapping: std.AutoHashMapUnmanaged(Card, u32),
+    blank: u32,
+    back: u32,
+
+    pub fn deinit(this: *@This(), gpa: std.mem.Allocator) void {
+        this.tilesheet.deinit();
+        this.mapping.deinit(gpa);
+    }
+
+    pub fn getTileForCard(this: @This(), card: Card) u32 {
+        return this.mapping.get(card) orelse 0;
+    }
+};
+
+pub fn loadSmallCards(gpa: std.mem.Allocator) !DeckSprites {
+    var tilesheet = try TileSheet.init(.{
+        .allocator = gpa,
+        .image_file_contents = @embedFile("./cardsSmall_tilemap.png"),
+        .tile_offset = .{ 0, 0 },
+        .tile_size = .{ 16, 16 },
+        .tile_stride = .{ 17, 17 },
+        .texture_options = .{
+            .min_filter = .nearest,
+            .mag_filter = .nearest,
+        },
+    });
+    errdefer tilesheet.deinit();
+
+    var mapping = std.AutoHashMap(Card, u32).init(gpa);
+    errdefer mapping.deinit();
+    try mapping.ensureTotalCapacity(52);
+
+    const hearts_start_index: u32 = 0;
+    for (0..13) |rank| {
+        mapping.putAssumeCapacityNoClobber(
+            Card{ .suit = .hearts, .rank = @intCast(rank + 1) },
+            hearts_start_index + @as(u32, @intCast(rank)),
+        );
+    }
+
+    const diamonds_start_index: u32 = 14;
+    for (0..13) |rank| {
+        mapping.putAssumeCapacityNoClobber(
+            Card{ .suit = .diamonds, .rank = @intCast(rank + 1) },
+            diamonds_start_index + @as(u32, @intCast(rank)),
+        );
+    }
+
+    const clubs_start_index: u32 = 28;
+    for (0..13) |rank| {
+        mapping.putAssumeCapacityNoClobber(
+            Card{ .suit = .clubs, .rank = @intCast(rank + 1) },
+            clubs_start_index + @as(u32, @intCast(rank)),
+        );
+    }
+
+    const spades_start_index: u32 = 42;
+    for (0..13) |rank| {
+        mapping.putAssumeCapacityNoClobber(
+            Card{ .suit = .spades, .rank = @intCast(rank + 1) },
+            spades_start_index + @as(u32, @intCast(rank)),
+        );
+    }
+
+    return DeckSprites{
+        .tilesheet = tilesheet,
+        .mapping = mapping.unmanaged,
+        // TODO: add better graphic for blank card
+        .blank = 59,
+        .back = 59,
+    };
+}
+
+pub fn loadMediumCards(gpa: std.mem.Allocator) !DeckSprites {
+    var tilesheet = try TileSheet.init(.{
+        .allocator = gpa,
+        .image_file_contents = @embedFile("./cardsMedium_tilemap.png"),
+        .tile_offset = .{ 6, 2 },
+        .tile_size = .{ 20, 29 },
+        .tile_stride = .{ 33, 33 },
+        .texture_options = .{
+            .min_filter = .nearest,
+            .mag_filter = .nearest,
+        },
+    });
+    errdefer tilesheet.deinit();
+
+    var mapping = std.AutoHashMap(Card, u32).init(gpa);
+    errdefer mapping.deinit();
+    try mapping.ensureTotalCapacity(52);
+
+    const hearts_start_index: u32 = 0;
+    for (0..13) |rank| {
+        mapping.putAssumeCapacityNoClobber(
+            Card{ .suit = .hearts, .rank = @intCast(rank + 1) },
+            hearts_start_index + @as(u32, @intCast(rank)),
+        );
+    }
+
+    const diamonds_start_index: u32 = 15;
+    for (0..13) |rank| {
+        mapping.putAssumeCapacityNoClobber(
+            Card{ .suit = .diamonds, .rank = @intCast(rank + 1) },
+            diamonds_start_index + @as(u32, @intCast(rank)),
+        );
+    }
+
+    const clubs_start_index: u32 = 30;
+    for (0..13) |rank| {
+        mapping.putAssumeCapacityNoClobber(
+            Card{ .suit = .clubs, .rank = @intCast(rank + 1) },
+            clubs_start_index + @as(u32, @intCast(rank)),
+        );
+    }
+
+    const spades_start_index: u32 = 45;
+    for (0..13) |rank| {
+        mapping.putAssumeCapacityNoClobber(
+            Card{ .suit = .spades, .rank = @intCast(rank + 1) },
+            spades_start_index + @as(u32, @intCast(rank)),
+        );
+    }
+
+    return DeckSprites{
+        .tilesheet = tilesheet,
+        .mapping = mapping.unmanaged,
+        .blank = 14,
+        .back = 29,
+    };
+}
+
+pub fn loadLargeCards(gpa: std.mem.Allocator) !DeckSprites {
+    var tilesheet = try TileSheet.init(.{
+        .allocator = gpa,
+        .image_file_contents = @embedFile("./cardsLarge_tilemap.png"),
+        .tile_offset = .{ 11, 2 },
+        .tile_size = .{ 41, 60 },
+        .tile_stride = .{ 65, 65 },
+        .texture_options = .{
+            .min_filter = .nearest,
+            .mag_filter = .nearest,
+        },
+    });
+    errdefer tilesheet.deinit();
+
+    var mapping = std.AutoHashMap(Card, u32).init(gpa);
+    errdefer mapping.deinit();
+    try mapping.ensureTotalCapacity(52);
+
+    const hearts_start_index: u32 = 0;
+    for (0..13) |rank| {
+        mapping.putAssumeCapacityNoClobber(
+            Card{ .suit = .hearts, .rank = @intCast(rank + 1) },
+            hearts_start_index + @as(u32, @intCast(rank)),
+        );
+    }
+
+    const diamonds_start_index: u32 = 14;
+    for (0..13) |rank| {
+        mapping.putAssumeCapacityNoClobber(
+            Card{ .suit = .diamonds, .rank = @intCast(rank + 1) },
+            diamonds_start_index + @as(u32, @intCast(rank)),
+        );
+    }
+
+    const clubs_start_index: u32 = 28;
+    for (0..13) |rank| {
+        mapping.putAssumeCapacityNoClobber(
+            Card{ .suit = .clubs, .rank = @intCast(rank + 1) },
+            clubs_start_index + @as(u32, @intCast(rank)),
+        );
+    }
+
+    const spades_start_index: u32 = 42;
+    for (0..13) |rank| {
+        mapping.putAssumeCapacityNoClobber(
+            Card{ .suit = .spades, .rank = @intCast(rank + 1) },
+            spades_start_index + @as(u32, @intCast(rank)),
+        );
+    }
+
+    return DeckSprites{
+        .tilesheet = tilesheet,
+        .mapping = mapping.unmanaged,
+        .blank = 13,
+        .back = 27,
+    };
+}
+
+const seizer = @import("seizer");
+const gl = seizer.gl;
+const std = @import("std");

src/main.zig

@@ -1,89 +1,110 @@
 var gl_binding: gl.Binding = undefined;
 
-const Suit = enum(u2) {
-    clubs = 0b00,
-    spades = 0b01,
-    hearts = 0b10,
-    diamonds = 0b11,
+const HandlerError = error{OutOfMemory};
+const Handler = *const fn (std.mem.Allocator, Request) HandlerError!Response;
 
-    pub fn color(this: @This()) u1 {
-        return (@intFromEnum(this) & 0b10) >> 1;
-    }
+const Request = struct {
+    game_state: GameState,
+    command: ?[]const u8,
 };
-const Card = packed struct(u6) {
-    suit: Suit,
-    rank: u4,
+const Response = union(enum) {
+    page: Element,
+    transition: struct {
+        game_state: GameState,
+        can_undo: bool,
+    },
 };
 
-/// A texture with a regular grid of sprites
-const TileSheet = struct {
-    texture: seizer.Texture,
-    tile_size: [2]u32,
+const GameState = struct {
+    allocator: std.mem.Allocator,
+    prng: std.rand.DefaultPrng,
+    handler: Handler,
+    draw_pile: std.ArrayListUnmanaged(Card),
+    discard_pile: std.ArrayListUnmanaged(Card),
+    hands: []std.ArrayListUnmanaged(Card),
 
-    pub const InitOptions = struct {
-        allocator: std.mem.Allocator,
-        image_file_contents: []const u8,
-        tile_size: [2]u32,
-        texture_options: seizer.Texture.InitFromFileOptions = .{},
-    };
+    pub fn init(allocator: std.mem.Allocator, seed: u64, num_players: usize) !@This() {
+        var draw_pile = std.ArrayListUnmanaged(Card).fromOwnedSlice(try makeStandardDeck(allocator));
+        errdefer draw_pile.deinit(allocator);
+
+        var prng = std.rand.DefaultPrng.init(seed);
+
+        prng.random().shuffle(Card, draw_pile.items);
+
+        const cards_per_player: usize = switch (num_players) {
+            1, 2 => 7,
+            3, 4 => 6,
+            else => unreachable,
+        };
+
+        const hands = try allocator.alloc(std.ArrayListUnmanaged(Card), num_players);
+        errdefer allocator.free(hands);
+        for (hands) |*hand| {
+            hand.* = try std.ArrayListUnmanaged(Card).initCapacity(allocator, cards_per_player);
+            for (0..cards_per_player) |_| {
+                hand.appendAssumeCapacity(draw_pile.pop());
+            }
+        }
+
+        var discard_pile = try std.ArrayListUnmanaged(Card).initCapacity(allocator, 52);
+        errdefer discard_pile.deinit(allocator);
+
+        // start game with one card in the discard pile
+        discard_pile.appendAssumeCapacity(draw_pile.pop());
 
-    pub fn init(options: InitOptions) !@This() {
-        const texture = try seizer.Texture.initFromFileContents(
-            options.allocator,
-            options.image_file_contents,
-            options.texture_options,
-        );
         return @This(){
-            .texture = texture,
-            .tile_size = options.tile_size,
+            .allocator = allocator,
+            .prng = prng,
+            .handler = &drawCardHandler,
+            .draw_pile = draw_pile,
+            .discard_pile = discard_pile,
+            .hands = hands,
         };
     }
 
     pub fn deinit(this: *@This()) void {
-        this.texture.deinit();
+        this.draw_pile.deinit(this.allocator);
+        this.discard_pile.deinit(this.allocator);
+        for (this.hands) |*hand| {
+            hand.deinit(this.allocator);
+        }
+        this.allocator.free(this.hands);
     }
 
-    pub fn renderTile(this: @This(), canvas: *seizer.Canvas, tile_id: u32, pos: [2]f32, options: struct {
-        size: ?[2]f32 = null,
-    }) void {
-        const texture_sizef = [2]f32{
-            @floatFromInt(this.texture.size[0]),
-            @floatFromInt(this.texture.size[1]),
+    pub fn clone(this: @This(), allocator: std.mem.Allocator) !@This() {
+        const hands = try allocator.alloc(std.ArrayListUnmanaged(Card), this.hands.len);
+        for (hands, this.hands) |*hand_clone, hand| {
+            hand_clone.* = try hand.clone(allocator);
+        }
+
+        return @This(){
+            .allocator = allocator,
+            .prng = this.prng,
+            .handler = this.handler,
+            .draw_pile = try this.draw_pile.clone(allocator),
+            .discard_pile = try this.discard_pile.clone(allocator),
+            .hands = hands,
         };
-        const tile_sizef = [2]f32{
-            @floatFromInt(this.tile_size[0]),
-            @floatFromInt(this.tile_size[1]),
-        };
-        const size_in_tiles = [2]u32{
-            @as(u32, @intCast(this.texture.size[0])) / this.tile_size[0],
-            @as(u32, @intCast(this.texture.size[1])) / this.tile_size[1],
-        };
-        const pos_in_tiles = [2]u32{
-            tile_id % size_in_tiles[0],
-            tile_id / size_in_tiles[0],
-        };
-        const pos_in_tilesf = [2]f32{
-            @floatFromInt(pos_in_tiles[0]),
-            @floatFromInt(pos_in_tiles[1]),
-        };
-        const uv = seizer.geometry.AABB(f32){
-            .min = .{
-                (pos_in_tilesf[0] * tile_sizef[0]) / texture_sizef[0],
-                (pos_in_tilesf[1] * tile_sizef[1]) / texture_sizef[1],
-            },
-            .max = .{
-                ((pos_in_tilesf[0] + 1) * tile_sizef[0]) / texture_sizef[0],
-                ((pos_in_tilesf[1] + 1) * tile_sizef[1]) / texture_sizef[1],
-            },
-        };
-        _ = canvas.printText(.{ 0, 0 }, "uv = {}", .{uv}, .{});
-        canvas.rect(pos, options.size orelse tile_sizef, .{
-            .texture = this.texture.glTexture,
-            .uv = uv,
-        });
     }
 };
-// const cards_medium_spritesheet =
+
+pub fn makeStandardDeck(allocator: std.mem.Allocator) ![]Card {
+    var deck = try allocator.alloc(Card, 52);
+    errdefer allocator.free(deck);
+
+    var next_index: usize = 0;
+    for (0..4) |suit| {
+        for (1..14) |rank| {
+            deck[next_index] = Card{
+                .suit = @enumFromInt(suit),
+                .rank = @intCast(rank),
+            };
+            next_index += 1;
+        }
+    }
+
+    return deck;
+}
 
 pub fn main() !void {
     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
@@ -116,25 +137,135 @@ pub fn main() !void {
     gl.makeBindingCurrent(&gl_binding);
 
     // Set up input callbacks
+    var input_state: InputState = undefined;
+    _ = seizer.backend.glfw.c.glfwSetWindowUserPointer(window, &input_state);
+
+    _ = seizer.backend.glfw.c.glfwSetKeyCallback(window, &glfw_key_callback);
     _ = seizer.backend.glfw.c.glfwSetFramebufferSizeCallback(window, &glfw_framebuffer_size_callback);
 
-    var card_tilemap = try TileSheet.init(.{
-        .allocator = gpa.allocator(),
-        .image_file_contents = @embedFile("./cardsMedium_tilemap.png"),
-        .tile_size = .{ 32, 32 },
-        .texture_options = .{
-            .min_filter = .nearest,
-            .mag_filter = .nearest,
-        },
-    });
-    defer card_tilemap.deinit();
+    var card_tilemap_small: ?DeckSprites = null;
+    defer if (card_tilemap_small) |*tilemap| tilemap.deinit(gpa.allocator());
+
+    var card_tilemap_medium: ?DeckSprites = null;
+    defer if (card_tilemap_medium) |*tilemap| tilemap.deinit(gpa.allocator());
+
+    var card_tilemap_large: ?DeckSprites = null;
+    defer if (card_tilemap_large) |*tilemap| tilemap.deinit(gpa.allocator());
 
     var canvas = try seizer.Canvas.init(gpa.allocator(), .{});
     defer canvas.deinit(gpa.allocator());
 
+    // game state
+    var history = std.ArrayList(GameState).init(gpa.allocator());
+    defer {
+        for (history.items) |*state| {
+            state.deinit();
+        }
+        history.deinit();
+    }
+    try history.append(try GameState.init(gpa.allocator(), std.crypto.random.int(u64), 1));
+
+    var root_element: ?Element = null;
+    var response_arena = std.heap.ArenaAllocator.init(gpa.allocator());
+    defer response_arena.deinit();
+
+    var actions = std.ArrayList(Action).init(gpa.allocator());
+    defer actions.deinit();
+
+    // TODO: Restore hovered_action when undoing
+    var hovered_action: ?Action = null;
+
     while (seizer.backend.glfw.c.glfwWindowShouldClose(window) != seizer.backend.glfw.c.GLFW_TRUE) {
+        input_state = .{
+            .left = false,
+            .right = false,
+            .up = false,
+            .down = false,
+            .action = false,
+            .undo = false,
+        };
         seizer.backend.glfw.c.glfwPollEvents();
 
+        var request_command: ?[]const u8 = null;
+        defer if (request_command) |command| gpa.allocator().free(command);
+
+        if (hovered_action) |hovered| {
+            if (input_state.action) {
+                request_command = try gpa.allocator().dupe(u8, hovered.command);
+                root_element = null;
+                hovered_action = null;
+            }
+        } else if (actions.items.len > 0) {
+            hovered_action = actions.items[0];
+        }
+
+        if (input_state.undo and history.items.len > 1) {
+            var discarded_state = history.pop();
+            discarded_state.deinit();
+            root_element = null;
+            hovered_action = null;
+        }
+
+        if (hovered_action) |hovered| {
+            var direction = [2]f32{ 0, 0 };
+            if (input_state.left) {
+                direction[0] -= 1;
+            }
+            if (input_state.right) {
+                direction[0] += 1;
+            }
+            if (input_state.up) {
+                direction[1] -= 1;
+            }
+            if (input_state.down) {
+                direction[1] += 1;
+            }
+
+            var new_distance: ?f32 = null;
+            var new_action = hovered;
+            for (actions.items) |action| {
+                if (std.mem.eql(u8, action.command, hovered.command)) {
+                    continue;
+                }
+                if (distanceToAction(hovered.center, direction, action.center)) |distance| {
+                    if (new_distance == null or (new_distance != null and distance < new_distance.?)) {
+                        new_action = Action{
+                            .center = .{
+                                if (input_state.left or input_state.right) action.center[0] else hovered.center[0],
+                                if (input_state.up or input_state.down) action.center[1] else hovered.center[1],
+                            },
+                            .command = action.command,
+                        };
+                        new_distance = distance;
+                    }
+                }
+            }
+
+            hovered_action = new_action;
+        }
+
+        while (root_element == null) {
+            _ = response_arena.reset(.retain_capacity);
+            const current_state = history.items[history.items.len - 1];
+            const response = try current_state.handler(response_arena.allocator(), Request{
+                .game_state = current_state,
+                .command = request_command,
+            });
+
+            switch (response) {
+                .page => |page_root_element| root_element = page_root_element,
+                .transition => |transition| {
+                    if (!transition.can_undo) {
+                        for (history.items) |*state| {
+                            state.deinit();
+                        }
+                        history.clearRetainingCapacity();
+                    }
+                    try history.append(try transition.game_state.clone(gpa.allocator()));
+                },
+            }
+        }
+
         gl.clearColor(0.7, 0.5, 0.5, 1.0);
         gl.clear(gl.COLOR_BUFFER_BIT);
 
@@ -154,19 +285,613 @@ pub fn main() !void {
                 @floatFromInt(framebuffer_size[1]),
             },
         });
-        card_tilemap.renderTile(&canvas, 1, .{ 10, 10 }, .{});
-        // canvas.rect(.{ 10, 10 }, .{ @as(f32, @floatFromInt(card_tilemap.size[0])) / 15.0, @as(f32, @floatFromInt(card_tilemap.size[1])) / 10.0 }, .{
-        //     .texture = card_tilemap.glTexture,
-        //     .uv = .{ .min = .{ 0, 0 }, .max = .{ 1.0 / 15.0, 1.0 / 10.0 } },
-        // });
-        _ = canvas.writeText(.{ 50, 50 }, "Hello, world!", .{});
-        _ = canvas.printText(.{ 50, 100 }, "window_size = {}, {}\nframebuffer_size = {}, {}", .{ window_size[0], window_size[1], framebuffer_size[0], framebuffer_size[1] }, .{});
+
+        _ = canvas.printText(.{ 0, 0 }, "History len: {}", .{history.items.len}, .{});
+
+        switch (framebuffer_size[1]) {
+            0...300 => if (card_tilemap_small == null) {
+                card_tilemap_small = try assets.loadSmallCards(gpa.allocator());
+            },
+            301...1000 => if (card_tilemap_medium == null) {
+                card_tilemap_medium = try assets.loadMediumCards(gpa.allocator());
+            },
+            1001...std.math.maxInt(c_int) => if (card_tilemap_large == null) {
+                card_tilemap_large = try assets.loadLargeCards(gpa.allocator());
+            },
+            else => unreachable,
+        }
+
+        const deck_sprites = switch (framebuffer_size[1]) {
+            0...300 => card_tilemap_small.?,
+            301...1000 => card_tilemap_medium.?,
+            1001...std.math.maxInt(c_int) => card_tilemap_large.?,
+            else => unreachable,
+        };
+
+        if (root_element) |root| {
+            root.interface.render(
+                root.pointer,
+                &canvas,
+                .{
+                    .hovered = if (hovered_action) |ha| ha.command else null,
+                    .deck = deck_sprites,
+                },
+                .{ 0, 0 },
+                .{
+                    @floatFromInt(window_size[0]),
+                    @floatFromInt(window_size[1]),
+                },
+            );
+        }
+
         canvas.end();
 
         seizer.backend.glfw.c.glfwSwapBuffers(window);
+
+        if (root_element) |root| {
+            actions.clearRetainingCapacity();
+            try root.interface.get_actions(
+                root.pointer,
+                &actions,
+                .{
+                    .hovered = if (hovered_action) |ha| ha.command else null,
+                    .deck = deck_sprites,
+                },
+                .{ 0, 0 },
+                .{
+                    @floatFromInt(window_size[0]),
+                    @floatFromInt(window_size[1]),
+                },
+            );
+        }
     }
 }
 
+fn distanceToAction(origin: [2]f32, direction: [2]f32, other_pos: [2]f32) ?f32 {
+    const off_axis_dir = [2]f32{ direction[1], -direction[0] };
+    const offset = [2]f32{
+        other_pos[0] - origin[0],
+        other_pos[1] - origin[1],
+    };
+
+    // use dot product to check how in line with each direction the point of interest is
+    const in_axis_distance = offset[0] * direction[0] + offset[1] * direction[1];
+    const off_axis_distance = offset[0] * off_axis_dir[0] + offset[1] * off_axis_dir[1];
+
+    if (in_axis_distance > 0) {
+        return in_axis_distance + off_axis_distance * off_axis_distance;
+    } else {
+        return null;
+    }
+}
+
+const Action = struct {
+    center: [2]f32,
+    /// A string representing what should occur if this action is taken
+    command: []const u8,
+};
+
+const RenderResources = struct {
+    hovered: ?[]const u8,
+    deck: DeckSprites,
+};
+
+pub const Element = struct {
+    pointer: ?*anyopaque,
+    interface: *const Interface,
+
+    pub const Error = error{
+        OutOfMemory,
+    };
+
+    pub const Interface = struct {
+        minimum_size: *const fn (?*anyopaque, RenderResources) [2]f32,
+        render: *const fn (?*anyopaque, *seizer.Canvas, RenderResources, [2]f32, [2]f32) void,
+        get_actions: *const fn (?*anyopaque, *std.ArrayList(Action), RenderResources, [2]f32, [2]f32) Error!void,
+    };
+};
+
+pub const Page = struct {
+    allocator: std.mem.Allocator,
+    children: std.ArrayListUnmanaged(Child),
+
+    pub const Child = struct {
+        /// Where is the child attached on the parent? Imagine it as a pin going through
+        /// both the parent and child element. This defines where on the parent that pin
+        /// passes through.
+        ///
+        /// In a virtual coordinate where <0,0> = top-left, <1,1> = bottom-right, unless
+        /// the numbers are negative.
+        anchor_in_parent: [2]f32,
+        /// Where is the child attached on the parent? Imagine it as a pin going through
+        /// both the parent and child element. This defines where on the child that pin
+        /// passes through.
+        ///
+        /// In a virtual coordinate where <0,0> = top-left, <1,1> = bottom-right, unless
+        /// the numbers are negative.
+        anchor_in_child: [2]f32,
+        element: Element,
+    };
+
+    pub fn create(allocator: std.mem.Allocator) !*@This() {
+        const this = try allocator.create(@This());
+        errdefer allocator.destroy(this);
+        this.* = .{
+            .allocator = allocator,
+            .children = .{},
+        };
+        return this;
+    }
+
+    pub fn addElement(this: *@This(), anchor_in_parent: [2]f32, anchor_in_child: [2]f32, child_element: Element) !void {
+        try this.children.append(this.allocator, Child{
+            .anchor_in_parent = anchor_in_parent,
+            .anchor_in_child = anchor_in_child,
+            .element = child_element,
+        });
+    }
+
+    pub fn element(this: *@This()) Element {
+        return Element{
+            .pointer = this,
+            .interface = &Element.Interface{
+                .minimum_size = &element_minimum_size,
+                .render = &element_render,
+                .get_actions = &element_get_actions,
+            },
+        };
+    }
+
+    pub fn element_minimum_size(pointer: ?*anyopaque, render_resources: RenderResources) [2]f32 {
+        const this: *@This() = @ptrCast(@alignCast(pointer));
+
+        var minimum_size = [2]f32{ 0, 0 };
+        for (this.children.items) |child| {
+            const child_size = child.element.interface.minimum_size(child.element.pointer, render_resources);
+
+            minimum_size = .{
+                @max(minimum_size[0], child_size[0]),
+                @max(minimum_size[1], child_size[1]),
+            };
+        }
+
+        return minimum_size;
+    }
+
+    pub fn element_render(pointer: ?*anyopaque, canvas: *seizer.Canvas, render_resources: RenderResources, min: [2]f32, max: [2]f32) void {
+        const this: *@This() = @ptrCast(@alignCast(pointer));
+
+        const parent_size = [2]f32{
+            max[0] - min[0],
+            max[1] - min[1],
+        };
+
+        for (this.children.items) |child| {
+            const pos_in_parent = [2]f32{
+                child.anchor_in_parent[0] * parent_size[0],
+                child.anchor_in_parent[1] * parent_size[1],
+            };
+
+            const child_size = child.element.interface.minimum_size(child.element.pointer, render_resources);
+
+            const pos_in_child = [2]f32{
+                child.anchor_in_child[0] * child_size[0],
+                child.anchor_in_child[1] * child_size[1],
+            };
+
+            const child_min = [2]f32{
+                @max(min[0], pos_in_parent[0] - pos_in_child[0]),
+                @max(min[1], pos_in_parent[1] - pos_in_child[1]),
+            };
+            const child_max = [2]f32{
+                @min(max[0], pos_in_parent[0] + (child_size[0] - pos_in_child[0])),
+                @min(max[1], pos_in_parent[1] + (child_size[1] - pos_in_child[1])),
+            };
+
+            child.element.interface.render(child.element.pointer, canvas, render_resources, child_min, child_max);
+        }
+    }
+
+    pub fn element_get_actions(pointer: ?*anyopaque, actions: *std.ArrayList(Action), render_resources: RenderResources, min: [2]f32, max: [2]f32) Element.Error!void {
+        const this: *@This() = @ptrCast(@alignCast(pointer));
+
+        const parent_size = [2]f32{
+            max[0] - min[0],
+            max[1] - min[1],
+        };
+
+        for (this.children.items) |child| {
+            const pos_in_parent = [2]f32{
+                child.anchor_in_parent[0] * parent_size[0],
+                child.anchor_in_parent[1] * parent_size[1],
+            };
+
+            const child_size = child.element.interface.minimum_size(child.element.pointer, render_resources);
+
+            const pos_in_child = [2]f32{
+                child.anchor_in_child[0] * child_size[0],
+                child.anchor_in_child[1] * child_size[1],
+            };
+
+            const child_min = [2]f32{
+                pos_in_parent[0] - pos_in_child[0],
+                pos_in_parent[1] - pos_in_child[1],
+            };
+            const child_max = [2]f32{
+                pos_in_parent[0] + (child_size[0] - pos_in_child[0]),
+                pos_in_parent[1] + (child_size[1] - pos_in_child[1]),
+            };
+
+            try child.element.interface.get_actions(child.element.pointer, actions, render_resources, child_min, child_max);
+        }
+    }
+};
+
+pub const HBox = struct {
+    allocator: std.mem.Allocator,
+    children: std.ArrayListUnmanaged(Element),
+
+    pub fn create(allocator: std.mem.Allocator) !*@This() {
+        const this = try allocator.create(@This());
+        errdefer allocator.destroy(this);
+        this.* = .{
+            .allocator = allocator,
+            .children = .{},
+        };
+        return this;
+    }
+
+    pub fn addElement(this: *@This(), child_element: Element) !void {
+        try this.children.append(this.allocator, child_element);
+    }
+
+    pub fn element(this: *@This()) Element {
+        return Element{
+            .pointer = this,
+            .interface = &Element.Interface{
+                .minimum_size = &element_minimum_size,
+                .render = &element_render,
+                .get_actions = &element_get_actions,
+            },
+        };
+    }
+
+    pub fn element_minimum_size(pointer: ?*anyopaque, render_resources: RenderResources) [2]f32 {
+        const this: *@This() = @ptrCast(@alignCast(pointer));
+
+        var minimum_size = [2]f32{ 0, 0 };
+        for (this.children.items) |child| {
+            const child_size = child.interface.minimum_size(child.pointer, render_resources);
+
+            minimum_size = .{
+                minimum_size[0] + child_size[0],
+                @max(minimum_size[1], child_size[1]),
+            };
+        }
+
+        return minimum_size;
+    }
+
+    pub fn element_render(pointer: ?*anyopaque, canvas: *seizer.Canvas, render_resources: RenderResources, min: [2]f32, max: [2]f32) void {
+        const this: *@This() = @ptrCast(@alignCast(pointer));
+
+        if (this.children.items.len == 0) return;
+
+        const parent_size = [2]f32{
+            max[0] - min[0],
+            max[1] - min[1],
+        };
+
+        var filled_space: f32 = 0;
+        for (this.children.items) |child| {
+            const child_size = child.interface.minimum_size(child.pointer, render_resources);
+
+            filled_space += child_size[0];
+        }
+
+        const empty_space = parent_size[0] - filled_space;
+
+        const num_spaces = if (empty_space > 0) this.children.items.len + 1 else this.children.items.len - 1;
+
+        const space_around = empty_space / @as(f32, @floatFromInt(num_spaces));
+
+        var x: f32 = min[0] + @max(space_around, 0);
+        for (this.children.items) |child| {
+            const child_size = child.interface.minimum_size(child.pointer, render_resources);
+
+            const child_min = [2]f32{ x, min[1] };
+            const child_max = [2]f32{ x + child_size[0], max[1] };
+
+            child.interface.render(child.pointer, canvas, render_resources, child_min, child_max);
+
+            x += child_size[0] + space_around;
+        }
+    }
+
+    pub fn element_get_actions(pointer: ?*anyopaque, actions: *std.ArrayList(Action), render_resources: RenderResources, min: [2]f32, max: [2]f32) Element.Error!void {
+        const this: *@This() = @ptrCast(@alignCast(pointer));
+
+        if (this.children.items.len == 0) return;
+
+        const parent_size = [2]f32{
+            max[0] - min[0],
+            max[1] - min[1],
+        };
+
+        var filled_space: f32 = 0;
+        for (this.children.items) |child| {
+            const child_size = child.interface.minimum_size(child.pointer, render_resources);
+
+            filled_space += child_size[0];
+        }
+
+        const empty_space = parent_size[0] - filled_space;
+
+        const space_around = empty_space / @as(f32, @floatFromInt((this.children.items.len + 1)));
+
+        var x: f32 = min[0] + space_around;
+        for (this.children.items) |child| {
+            const child_size = child.interface.minimum_size(child.pointer, render_resources);
+
+            const child_min = [2]f32{ x, min[1] };
+            const child_max = [2]f32{ x + child_size[0], max[1] };
+
+            try child.interface.get_actions(child.pointer, actions, render_resources, child_min, child_max);
+
+            x += child_size[0] + space_around;
+        }
+    }
+};
+
+pub const Pile = struct {
+    allocator: std.mem.Allocator,
+    cards: []Card,
+    hidden: bool = false,
+    command: ?[]const u8 = null,
+
+    pub fn create(allocator: std.mem.Allocator, cards: []const Card) !*@This() {
+        const this = try allocator.create(@This());
+        errdefer allocator.destroy(this);
+
+        const cards_owned = try allocator.dupe(Card, cards);
+        errdefer allocator.free(cards_owned);
+
+        this.* = .{
+            .allocator = allocator,
+            .cards = cards_owned,
+        };
+        return this;
+    }
+
+    pub fn element(this: *@This()) Element {
+        return Element{
+            .pointer = this,
+            .interface = &Element.Interface{
+                .minimum_size = &element_minimum_size,
+                .render = &element_render,
+                .get_actions = &element_get_actions,
+            },
+        };
+    }
+
+    pub fn element_minimum_size(pointer: ?*anyopaque, render_resources: RenderResources) [2]f32 {
+        const this: *@This() = @ptrCast(@alignCast(pointer));
+
+        return .{
+            @floatFromInt(render_resources.deck.tilesheet.tile_size[0]),
+            @as(f32, (@floatFromInt(render_resources.deck.tilesheet.tile_size[1]))) + @as(f32, (@floatFromInt(render_resources.deck.tilesheet.tile_size[1]))) * @as(f32, @floatFromInt(this.cards.len)) / 52.0 * 0.25,
+        };
+    }
+
+    pub fn element_render(pointer: ?*anyopaque, canvas: *seizer.Canvas, render_resources: RenderResources, min: [2]f32, max: [2]f32) void {
+        const this: *@This() = @ptrCast(@alignCast(pointer));
+
+        const start_y: f32 = max[1] - @as(f32, @floatFromInt(render_resources.deck.tilesheet.tile_size[1]));
+
+        for (this.cards, 0..) |card, i| {
+            const oy = -@as(f32, @floatFromInt(i)) * (@as(f32, @floatFromInt(render_resources.deck.tilesheet.tile_size[1])) / (52.0 * 4));
+            if (this.hidden) {
+                render_resources.deck.tilesheet.renderTile(canvas, render_resources.deck.back, .{
+                    min[0],
+                    start_y + oy,
+                }, .{});
+            } else {
+                render_resources.deck.tilesheet.renderTile(canvas, render_resources.deck.getTileForCard(card), .{
+                    min[0],
+                    start_y + oy,
+                }, .{});
+            }
+        }
+
+        if (render_resources.hovered != null and this.command != null and std.mem.eql(u8, render_resources.hovered.?, this.command.?)) {
+            const oy = -@as(f32, @floatFromInt(this.cards.len)) * (@as(f32, @floatFromInt(render_resources.deck.tilesheet.tile_size[1])) / (52.0 * 4));
+            canvas.rect(
+                .{ min[0], start_y + oy },
+                .{ @floatFromInt(render_resources.deck.tilesheet.tile_size[0]), @floatFromInt(render_resources.deck.tilesheet.tile_size[1]) },
+                .{ .color = .{ 0xAA, 0xFF, 0xAA, 0x60 } },
+            );
+        }
+    }
+
+    pub fn element_get_actions(pointer: ?*anyopaque, actions: *std.ArrayList(Action), render_resources: RenderResources, min: [2]f32, max: [2]f32) Element.Error!void {
+        const this: *@This() = @ptrCast(@alignCast(pointer));
+
+        if (this.command) |command| {
+            const center = [2]f32{
+                min[0] + @as(f32, @floatFromInt(render_resources.deck.tilesheet.tile_size[0])) / 2,
+                max[1] - @as(f32, @floatFromInt(render_resources.deck.tilesheet.tile_size[1])) * (2.0 - @as(f32, @floatFromInt(this.cards.len)) / (52.0 * 4)),
+            };
+
+            try actions.append(.{
+                .center = center,
+                .command = command,
+            });
+        }
+    }
+};
+
+pub const CardElement = struct {
+    allocator: std.mem.Allocator,
+    visual: Visual,
+    command: ?[]const u8,
+
+    const Visual = union(enum) {
+        back,
+        card: Card,
+    };
+
+    pub fn create(allocator: std.mem.Allocator, options: struct { visual: Visual, command: ?[]const u8 }) !*@This() {
+        const this = try allocator.create(@This());
+        errdefer allocator.destroy(this);
+
+        this.* = .{
+            .allocator = allocator,
+            .visual = options.visual,
+            .command = options.command,
+        };
+        return this;
+    }
+
+    pub fn element(this: *@This()) Element {
+        return Element{
+            .pointer = this,
+            .interface = &Element.Interface{
+                .minimum_size = &element_minimum_size,
+                .render = &element_render,
+                .get_actions = &element_get_actions,
+            },
+        };
+    }
+
+    pub fn element_minimum_size(pointer: ?*anyopaque, render_resources: RenderResources) [2]f32 {
+        const this: *@This() = @ptrCast(@alignCast(pointer));
+        _ = this;
+
+        return .{
+            @as(f32, @floatFromInt(render_resources.deck.tilesheet.tile_size[0])),
+            @as(f32, @floatFromInt(render_resources.deck.tilesheet.tile_size[1])),
+        };
+    }
+
+    pub fn element_render(pointer: ?*anyopaque, canvas: *seizer.Canvas, render_resources: RenderResources, min: [2]f32, max: [2]f32) void {
+        const this: *@This() = @ptrCast(@alignCast(pointer));
+
+        switch (this.visual) {
+            .back => render_resources.deck.tilesheet.renderTile(
+                canvas,
+                render_resources.deck.back,
+                .{ min[0], min[1] },
+                .{},
+            ),
+            .card => |card| render_resources.deck.tilesheet.renderTile(
+                canvas,
+                render_resources.deck.getTileForCard(card),
+                .{ min[0], min[1] },
+                .{},
+            ),
+        }
+
+        if (render_resources.hovered != null and this.command != null and std.mem.eql(u8, render_resources.hovered.?, this.command.?)) {
+            canvas.rect(
+                min,
+                .{ max[0] - min[0], max[1] - min[1] },
+                .{ .color = .{ 0xAA, 0xFF, 0xAA, 0x60 } },
+            );
+        }
+    }
+
+    pub fn element_get_actions(pointer: ?*anyopaque, actions: *std.ArrayList(Action), render_resources: RenderResources, min: [2]f32, max: [2]f32) Element.Error!void {
+        const this: *@This() = @ptrCast(@alignCast(pointer));
+
+        _ = render_resources;
+
+        if (this.command) |command| {
+            try actions.append(.{
+                .center = [2]f32{
+                    (min[0] + max[0]) / 2,
+                    (min[1] + max[1]) / 2,
+                },
+                .command = command,
+            });
+        }
+    }
+};
+
+/// Handler at the start of a turn, while the player is drawing a card.
+fn drawCardHandler(arena: std.mem.Allocator, request: Request) HandlerError!Response {
+    if (request.command) |command| {
+        if (std.mem.eql(u8, command, "draw draw_pile")) {
+            var new_game_state = try request.game_state.clone(arena);
+            try new_game_state.hands[0].append(arena, new_game_state.draw_pile.pop());
+            new_game_state.handler = &playerTurnHandler;
+            return Response{ .transition = .{
+                .game_state = new_game_state,
+                .can_undo = false,
+            } };
+        } else if (std.mem.eql(u8, command, "draw discard_pile")) {
+            var new_game_state = try request.game_state.clone(arena);
+            try new_game_state.hands[0].append(arena, new_game_state.discard_pile.pop());
+            new_game_state.handler = &playerTurnHandler;
+            return Response{ .transition = .{
+                .game_state = new_game_state,
+                .can_undo = true,
+            } };
+        }
+    }
+
+    var draw_pile = try Pile.create(arena, request.game_state.draw_pile.items);
+    draw_pile.hidden = true;
+    draw_pile.command = "draw draw_pile";
+
+    var discard_pile = try Pile.create(arena, request.game_state.discard_pile.items);
+    discard_pile.command = "draw discard_pile";
+
+    var hand = try HBox.create(arena);
+    for (request.game_state.hands[0].items) |card| {
+        var card_element = try CardElement.create(arena, .{
+            .visual = .{ .card = card },
+            .command = null,
+        });
+        try hand.addElement(card_element.element());
+    }
+
+    var draw_discard_hbox = try HBox.create(arena);
+    try draw_discard_hbox.addElement(draw_pile.element());
+    try draw_discard_hbox.addElement(discard_pile.element());
+
+    var page = try Page.create(arena);
+    try page.addElement(.{ 0.5, 0.5 }, .{ 0.5, 0.5 }, draw_discard_hbox.element());
+    try page.addElement(.{ 0.5, 1 }, .{ 0.5, 1 }, hand.element());
+
+    return Response{ .page = page.element() };
+}
+
+fn playerTurnHandler(arena: std.mem.Allocator, request: Request) HandlerError!Response {
+    var draw_pile = try Pile.create(arena, request.game_state.draw_pile.items);
+    draw_pile.hidden = true;
+
+    var discard_pile = try Pile.create(arena, request.game_state.discard_pile.items);
+
+    var hand = try HBox.create(arena);
+    for (request.game_state.hands[0].items) |card| {
+        var card_element = try CardElement.create(arena, .{
+            .visual = .{ .card = card },
+            .command = "mark",
+        });
+        try hand.addElement(card_element.element());
+    }
+
+    var draw_discard_hbox = try HBox.create(arena);
+    try draw_discard_hbox.addElement(draw_pile.element());
+    try draw_discard_hbox.addElement(discard_pile.element());
+
+    var page = try Page.create(arena);
+    try page.addElement(.{ 0.5, 0.5 }, .{ 0.5, 0.5 }, draw_discard_hbox.element());
+    try page.addElement(.{ 0.5, 1 }, .{ 0.5, 1 }, hand.element());
+
+    return Response{ .page = page.element() };
+}
+
 fn glfw_framebuffer_size_callback(window: ?*seizer.backend.glfw.c.GLFWwindow, width: c_int, height: c_int) callconv(.C) void {
     _ = window;
     gl.viewport(
@@ -177,6 +902,37 @@ fn glfw_framebuffer_size_callback(window: ?*seizer.backend.glfw.c.GLFWwindow, wi
     );
 }
 
+const InputState = struct {
+    left: bool,
+    right: bool,
+    up: bool,
+    down: bool,
+    action: bool,
+    undo: bool,
+};
+
+fn glfw_key_callback(window: ?*seizer.backend.glfw.c.GLFWwindow, key: c_int, scancode: c_int, action: c_int, mods: c_int) callconv(.C) void {
+    const input_state = @as(*InputState, @alignCast(@ptrCast(seizer.backend.glfw.c.glfwGetWindowUserPointer(window))));
+
+    _ = scancode;
+    _ = mods;
+    if (action == seizer.backend.glfw.c.GLFW_PRESS) {
+        switch (key) {
+            seizer.backend.glfw.c.GLFW_KEY_LEFT => input_state.left = true,
+            seizer.backend.glfw.c.GLFW_KEY_RIGHT => input_state.right = true,
+            seizer.backend.glfw.c.GLFW_KEY_UP => input_state.up = true,
+            seizer.backend.glfw.c.GLFW_KEY_DOWN => input_state.down = true,
+            seizer.backend.glfw.c.GLFW_KEY_Z => input_state.action = true,
+            seizer.backend.glfw.c.GLFW_KEY_BACKSPACE => input_state.undo = true,
+            else => {},
+        }
+    }
+}
+
+const DeckSprites = assets.DeckSprites;
+const Card = assets.Card;
+
+const assets = @import("./assets.zig");
 const seizer = @import("seizer");
 const gl = seizer.gl;
 const std = @import("std");