Updating framepacing example, removing post-tick lifecycle function after adding fixed-tick

Author: Interrupt

src/examples/framepacing.zig

@@ -21,6 +21,8 @@ const state = struct {
     var start_x: f32 = 120.0;
     var x_pos: f32 = 120.0;
     var x_pos_delta: f32 = 120.0;
+    var x_pos_fixed: f32 = 120.0;
+    var speed: f32 = 300.0;
 };
 
 // This example shows the simple debug drawing functions.
@@ -37,6 +39,7 @@ pub fn registerModule() !void {
         .name = "frame_pacing_test",
         .init_fn = on_init,
         .tick_fn = on_tick,
+        .fixed_tick_fn = on_fixed_tick,
         .draw_fn = on_draw,
         .cleanup_fn = on_cleanup,
     };
@@ -60,8 +63,8 @@ fn on_init() void {
 }
 
 fn on_tick(delta: f32) void {
-    state.x_pos += (1.0 / 60.0) * 300.0;
-    state.x_pos_delta += delta * 300.0;
+    state.x_pos += (1.0 / 60.0) * state.speed;
+    state.x_pos_delta += delta * state.speed;
 
     if(state.x_pos > 600.0)
         state.x_pos = 0.0;
@@ -73,10 +76,28 @@ fn on_tick(delta: f32) void {
         std.os.exit(0);
 }
 
+fn on_fixed_tick(fixed_delta: f32) void {
+    state.x_pos_fixed += fixed_delta * state.speed;
+
+    if(state.x_pos_fixed > 600.0)
+        state.x_pos_fixed = 0.0;
+}
+
 fn on_draw() void {
     // Draw our debug cat image, but use the color override to tint it!
-    graphics.drawDebugRectangle(texture, state.start_x + state.x_pos, 120.0, 100.0, 100.0, colors.white);
-    graphics.drawDebugRectangle(texture, state.start_x + state.x_pos_delta, 260.0, 100.0, 100.0, colors.white);
+    var y_pos: f32 = 100.0;
+    const y_spacing: f32 = 120.0;
+
+    graphics.drawDebugText(10, y_pos - 30, "raw tick:");
+    graphics.drawDebugRectangle(texture, state.start_x + state.x_pos, y_pos, 100.0, 100.0, colors.white);
+    y_pos += y_spacing;
+
+    graphics.drawDebugText(10, y_pos - 90, "delta tick:");
+    graphics.drawDebugRectangle(texture, state.start_x + state.x_pos_delta, y_pos, 100.0, 100.0, colors.white);
+    y_pos += y_spacing;
+
+    graphics.drawDebugText(10, y_pos - 150, "fixed tick:");
+    graphics.drawDebugRectangle(texture, state.start_x + state.x_pos_fixed, y_pos, 100.0, 100.0, colors.white);
 }
 
 fn on_cleanup() void {

src/framework/modules.zig

@@ -14,7 +14,7 @@ pub const Module = struct {
     start_fn: ?*const fn () void = null,
     stop_fn: ?*const fn () void = null,
     tick_fn: ?*const fn (f32) void = null,
-    post_tick_fn: ?*const fn () void = null,
+    fixed_tick_fn: ?*const fn (f32) void = null,
     pre_draw_fn: ?*const fn () void = null,
     draw_fn: ?*const fn () void = null,
     post_draw_fn: ?*const fn () void = null,
@@ -72,10 +72,14 @@ pub fn tickModules(delta_time: f32) void {
         if (module.value_ptr.tick_fn != null)
             module.value_ptr.tick_fn.?(delta_time);
     }
-    it = modules.iterator();
+}
+
+/// Calls the fixed tick and function of all modules
+pub fn fixedTickModules(fixed_delta_time: f32) void {
+    var it = modules.iterator();
     while (it.next()) |module| {
-        if (module.value_ptr.post_tick_fn != null)
-            module.value_ptr.post_tick_fn.?();
+        if (module.value_ptr.fixed_tick_fn != null)
+            module.value_ptr.fixed_tick_fn.?(fixed_delta_time);
     }
 }
 

src/framework/platform/app.zig

@@ -22,9 +22,9 @@ const state = struct {
     var target_fps: ?u64 = null;
     var target_fps_ns: u64 = undefined;
 
-    // Fixed timestamp length, if set
-    var fixed_timestep_delta_ns: ?u64 = null;
-    var fixed_timestep_delta_f: f32 = 0.0;
+    // Fixed timestep length - defaults to 40 per second
+    var fixed_timestep_delta_ns: ?u64 = @intFromFloat((1.0 / 40.0) * NS_PER_SECOND_F);
+    var fixed_timestep_delta_f: f32 = 1.0 / 40.0;
 
     // game loop timers
     var game_loop_timer: time.Timer = undefined;
@@ -139,14 +139,13 @@ fn on_frame() void {
         // keep ticking until we catch up to the actual time
         while (state.time_accumulator_ns >= fixed_delta_ns) {
             // fixed timestamp, tick at our constant rate
-            modules.tickModules(state.fixed_timestep_delta_f);
+            modules.fixedTickModules(state.fixed_timestep_delta_f);
             state.time_accumulator_ns -= fixed_delta_ns;
         }
-    } else {
-        // tick as fast as possible!
-        modules.tickModules(state.delta_time);
     }
 
+    modules.tickModules(state.delta_time);
+
     // tell modules we are getting ready to draw!
     modules.preDrawModules();
 

src/framework/platform/input.zig

@@ -165,7 +165,6 @@ const state = struct {
 pub fn registerModule() !void {
     const inputSubsystem = modules.Module{
         .name = "subsystem.input",
-        .post_tick_fn = on_post_tick,
         .post_draw_fn = on_post_draw,
     };
 
@@ -184,7 +183,7 @@ pub fn deinit() void {
 }
 
 /// App lifecycle event that happens after ticking
-fn on_post_tick() void {
+fn on_post_draw() void {
     // reset the 'just pressed' states
     for (0..state.keyboard_just_pressed.len) |i| {
         state.keyboard_just_pressed[i] = false;
@@ -200,9 +199,7 @@ fn on_post_tick() void {
     // reset the mouse delta state.
     state.mouse_dx = 0;
     state.mouse_dy = 0;
-}
 
-fn on_post_draw() void {
     // reset the mouse delta state.
     state.mouse_frame_dx = 0;
     state.mouse_frame_dy = 0;