Start using ECS by creating a camera entity

libs/flecs-zig-ble

@@ -0,0 +1 @@
+Subproject commit f48a6884caf656b49f416abdd3ce078fc93b1504

src/main.zig

@@ -4,10 +4,14 @@ const GeneralPurposeAllocator = std.heap.GeneralPurposeAllocator(.{});
 const core = @import("mach").core;
 const Renderer = @import("./renderer.zig");
 
+const flecszigble = @import("flecs-zig-ble");
+const World = flecszigble.World(void);
+
 pub const App = @This();
 
 gpa: GeneralPurposeAllocator,
 allocator: std.mem.Allocator,
+world: *World,
 random: std.rand.Random,
 
 renderer: *Renderer,
@@ -31,6 +35,18 @@ pub fn init(app: *App) !void {
     app.gpa = GeneralPurposeAllocator{};
     app.allocator = app.gpa.allocator();
 
+    // Initialize flecs-zig-ble and create a new Flecs world.
+    //
+    // Flecs is a library for using Entity Component System (ECS) design
+    // intuitively and efficiently. Entities can be created and have various
+    // components – and relationships to other entities – added to them.
+    //
+    // This data is stored in an in-memory database, which can be queried
+    // and modified. For example by using systems, you are able to get
+    // entities that match a set of components, and modify their values.
+    flecszigble.init(app.allocator);
+    app.world = try World.init();
+
     // Create a pseudo-random number generator, but initialize it with
     // a constant seed so we always get the same result when launching.
     var prng = std.rand.DefaultPrng.init(0);
@@ -47,6 +63,7 @@ pub fn deinit(app: *App) void {
     // in the order they were created in `init`.
     defer core.deinit();
     defer _ = app.gpa.deinit(); // TODO: Check for memory leaks?
+    defer app.world.deinit();
     defer app.renderer.deinit();
 }
 

src/renderer.zig

@@ -17,6 +17,23 @@ const primitives = @import("./primitives.zig");
 const VertexData = primitives.VertexData;
 const PrimitiveData = primitives.PrimitiveData;
 
+const flecszigble = @import("flecs-zig-ble");
+const Entity = flecszigble.Entity(void);
+
+const Transform = struct { value: Mat };
+const CameraPerspective = struct {
+    /// Vertical field of view (in degrees).
+    field_of_view: f32,
+    /// The near clip plane distance. Objects closer than this value are
+    /// "cut off". Should be set to a positive value close to zero, depending
+    /// on how close rendered objects typically get to the camera.
+    near_plane: f32,
+    /// The far clip place distance. Objects further than this value are
+    /// "cut off" and therefore won't be visible. Should be set to a larger
+    /// positive value, depending on how far objects can get from the camera.
+    far_plane: f32,
+};
+
 /// Holds data needed to render an object in a rendering pass.
 const ObjectData = struct {
     /// Bind group which associates model-related buffers with parameters
@@ -39,6 +56,7 @@ depth_texture_view: ?*gpu.TextureView = null,
 
 primitive_data: []PrimitiveData,
 object_data: []ObjectData,
+camera_entity: Entity,
 
 pub fn init(app: *App) !*Renderer {
     // A string buffer used to format objects' labels.
@@ -207,6 +225,12 @@ pub fn init(app: *App) !*Renderer {
         };
     }
 
+    _ = try app.world.component(Transform);
+    _ = try app.world.component(CameraPerspective);
+
+    const camera_entity = try app.world.entity(.{ .name = "Camera" }, .{ Transform, CameraPerspective });
+    camera_entity.set(CameraPerspective, .{ .field_of_view = 45.0, .near_plane = 0.05, .far_plane = 80.0 });
+
     const result = try app.allocator.create(Renderer);
     result.* = .{
         .app = app,
@@ -215,6 +239,7 @@ pub fn init(app: *App) !*Renderer {
         .camera_bind_group = camera_bind_group,
         .primitive_data = primitive_data,
         .object_data = object_data,
+        .camera_entity = camera_entity,
     };
 
     // Initialize the depth texture.
@@ -265,12 +290,23 @@ pub fn update(self: *Renderer) void {
     const camera_pos = vec(x, 2.0, z, 1.0);
     const view_matrix = zm.lookAtLh(camera_pos, vec(0, 0, 0, 1), vec(0, 1, 0, 1));
 
+    // Setting the transform here doesn't do anything because it's not used
+    // anywhere. In the future we would want to set the camera transform
+    // outside of the rendering step, and then get and use it here, instead.
+    self.camera_entity.set(Transform, .{ .value = view_matrix });
+    // TODO: Not sure if this is the proper transform, or actually inverted.
+
     // Set up a projection matrix using the size of the window.
     // The perspective projection will make things further away appear smaller.
     const width: f32 = @floatFromInt(core.descriptor.width);
     const height: f32 = @floatFromInt(core.descriptor.height);
-    const field_of_view = std.math.degreesToRadians(f32, 45.0);
-    const proj_matrix = zm.perspectiveFovLh(field_of_view, width / height, 0.05, 80.0);
+    const perspective = self.camera_entity.get(CameraPerspective).?;
+    const proj_matrix = zm.perspectiveFovLh(
+        std.math.degreesToRadians(f32, perspective.field_of_view),
+        width / height,
+        perspective.near_plane,
+        perspective.far_plane,
+    );
 
     const view_proj_matrix = zm.mul(view_matrix, proj_matrix);