just a bunch of cleanup to entities

src/Entity.zig

@@ -2,35 +2,77 @@ const assets = @import("assets.zig");
 const Layer = @import("Layer.zig");
 const Color = @import("Color.zig");
 const Recti = @import("geometry/Recti.zig");
+const std = @import("std");
 
 const Entity = @This();
 
+const EntityOptions = struct {
+	renders: bool = true,
+	updates: bool = true,
+	accepts_keyboard: bool = false,
+	accepts_mouse: bool = false,
+};
 
-ptr: *const anyopaque,
+ptr: *anyopaque,
+options: EntityOptions,
+destroyFn: *const fn(*const anyopaque) void,
+updateFn: *const fn(*anyopaque, f32) void,
 drawFn: *const fn(*const anyopaque) void,
 
+pub fn init(ptr: anytype, options: EntityOptions) Entity {
+	const MutablePointer = @TypeOf(ptr);
+	// @compileLog("Compiling Entity type for " ++ @typeName(MutablePointer));
 
-pub fn init(ptr: anytype) Entity {
-	const type_info = @typeInfo(@TypeOf(ptr));
+	const type_info = @typeInfo(MutablePointer);
 
+	// ensure the passed type is a mutable pointer
 	if(type_info != .Pointer) @compileError("Entity implementation must be a pointer");
+	// to a single thing
 	if(type_info.Pointer.size != .One) @compileError("Entity pointer must be a single item pointer");
+	// where that thing is a struct or opaque
+	switch (@typeInfo(type_info.Pointer.child)) {
+		.Struct => {},
+		else => @compileError("Entity pointer must point to a struct or opaque type"),
+	}
+	
+	// also take the const pointer type, as we will use both mutable an immutable pointers.
+	// some entities mutate and some do not
+	const ConstPointer = *const @typeInfo(MutablePointer).Pointer.child;
+	// @compileLog("const pointer type: " ++ @typeName(ConstPointer));
 
 	const gen = struct {
+		pub fn destroyImpl(pointer: *const anyopaque) void {
+			const self: ConstPointer = @ptrCast(@alignCast(pointer));
+			type_info.Pointer.child.destroy(self);
+		}
+		pub fn updateImpl(pointer: *anyopaque, dt: f32) void {
+			const self: MutablePointer = @ptrCast(@alignCast(pointer));
+			type_info.Pointer.child.update(self, dt);
+		}
 		pub fn drawImpl(pointer: *const anyopaque) void {
-			const self: @TypeOf(ptr) = @ptrCast(@alignCast(pointer));
+			const self: ConstPointer = @ptrCast(@alignCast(pointer));
 			type_info.Pointer.child.draw(self);
-			// @call(.{ .modifier = .always_inline }, ptr_info.Pointer.child.draw, .{ self });
-			// draw(self);
 		}
 	};
 
 	return .{
 		.ptr = ptr,
+		.options = options,
+		.destroyFn = gen.destroyImpl,
+
+		.updateFn = gen.updateImpl,
 		.drawFn = gen.drawImpl,
 	};
 }
 
+pub fn update(self: *const Entity, dt: f32) void {
+	self.updateFn(self.ptr, dt);
+}
+
 pub fn draw(self: *const Entity) void {
 	self.drawFn(self.ptr);
 }
+
+pub fn destroy(self: *const Entity) void {
+	self.destroyFn(self.ptr);
+}

src/Scene.zig

@@ -1,3 +1,5 @@
+const Scene = @This();
+
 const assets = @import("assets.zig");
 const Recti = @import("geometry/Recti.zig");
 const Layer = @import("Layer.zig");
@@ -7,13 +9,6 @@ const Terrain = @import("Terrain.zig");
 const std = @import("std");
 const ArrayList = std.ArrayList;
 
-const Scene = @This();
-// const DrawFunction = fn() void;
-// const UpdateFunction = fn(f32) void;
-
-// draw: DrawFunction,
-// update: 
-
 entities: ArrayList(Entity),
 
 pub fn new() Scene {
@@ -24,14 +19,46 @@ pub fn new() Scene {
 }
 
 pub fn destroy(self: *Scene) void {
+	for (self.entities.items) |entity| {
+		entity.destroy();
+	}
 	self.entities.deinit();
 }
 
 pub fn start(self: *Scene) !void {
-	const terrain = Terrain.new();
-	// terrain.entity();
+	const terrain = try Terrain.create();
+	try self.add(terrain);
+}
 
-	try self.entities.append(terrain.entity());
+// ---
+
+pub fn add(self: *Scene, instance_ptr: anytype) !void {
+	const instance_ptr_type = @TypeOf(instance_ptr);
+	const instance_ptr_type_info = @typeInfo(instance_ptr_type);
+
+	if (instance_ptr_type_info != .Pointer)
+		@compileError(
+			"Cannot add to scene type " ++
+			@typeName(instance_ptr_type) ++
+			"Must be a mutable pointer\n"
+		);
+	if (instance_ptr_type_info.Pointer.size != .One)
+		@compileError("Pointer size must be One");
+	if (instance_ptr_type_info.Pointer.is_const)
+		@compileError("Pointer must be mutable");
+
+	const instance_type = instance_ptr_type_info.Pointer.child;
+	
+	if (!@hasDecl(instance_type, "entity"))
+		@compileError("Pointer must be to a struct with fn entity() Entity");
+	
+	try self.entities.append(instance_ptr.entity());
+}
+
+pub fn update(self: *Scene, dt: f32) void {
+	for (self.entities.items) |entity| {
+		entity.update(dt);
+	}
 }
 
 pub fn draw(self: *Scene) void {
@@ -45,4 +72,16 @@ pub fn draw(self: *Scene) void {
 	assets.heart.draw(&Recti.from_xywh(80, 100, 32, 64), Layer.ENTITIES, Color.INDIGO);
 }
 
+// --- helpfer functions for entities themselves
 
+// an entity can choose to allocate itself however it pleases, but these
+// are good default functions that just throw things on the heap.
+pub fn allocate(instance: anytype) !*@TypeOf(instance) {
+	const ptr = try std.heap.page_allocator.create(@TypeOf(instance));
+	ptr.* = instance;
+	return ptr;
+}
+
+pub fn deallocate(instance: anytype) void {
+	std.heap.page_allocator.destroy(instance);
+}

src/Terrain.zig

@@ -5,21 +5,41 @@ const Layer = @import("Layer.zig");
 const Color = @import("Color.zig");
 const Recti = @import("geometry/Recti.zig");
 const Entity = @import("Entity.zig");
+const Scene = @import("Scene.zig");
 const std = @import("std");
 var prng = std.rand.DefaultPrng.init(0);
 
-size: u32 = 24,
-draw: u8 = 4,
+size: u16 = 24,
 
-pub fn new() Terrain {
-	return .{};
+pub fn entity(self: *Terrain) Entity {
+	return Entity.init(self, .{});
 }
 
-pub fn draw(_: *const Terrain) void {
+pub fn create() !*Terrain {
+	return try Scene.allocate(Terrain {
+		.size = 24,
+	});
+}
+
+pub fn destroy(self: *const Terrain) void {
+	Scene.deallocate(self);
+}
+
+pub fn update(self: *Terrain, _: f32) void {
+	if (prng.random().int(u8) == 34) {
+		self.size = self.size + 1;
+	}
+}
+
+pub fn draw(self: *const Terrain) void {
+	for(0..self.size) |y| {
+		for(0..self.size) |x| {
 			const idx: usize = @intFromFloat(@floor(prng.random().float(f32) * 4));
-	assets.terrain[idx].draw(&Recti.from_xywh(200, 100, 64, 64), Layer.FLOOR, Color.WHITE);
+			var grey = prng.random().float(f32);
+			grey /= 4.0;
+			grey += 3.0 / 4.0;
+			const rect = Recti.from_xywh(@intCast(100 + 16 * x), @intCast(100 + 16 * y), 16, 16);
+			assets.terrain[idx].draw(&rect, Layer.FLOOR, Color.rgba(grey, grey, grey, 1));
+		}
 	}
-
-pub fn entity(self: *const Terrain) Entity {
-	return Entity.init(self);
 }