From 18005ffa35de4be29b0b99bdbd237cea82e56acf Mon Sep 17 00:00:00 2001
From: "Jeffrey C. Ollie" <jeff@ocjtech.us>
Date: Sun, 4 Feb 2024 22:50:07 -0600
Subject: [PATCH] Fix shader time uniforms (#1462)

* fix shader time uniforms

* renderer/metal: one typo

---------

Co-authored-by: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
---
 src/renderer/Metal.zig         | 14 +++++++++++---
 src/renderer/opengl/custom.zig | 11 +++++++++--
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/src/renderer/Metal.zig b/src/renderer/Metal.zig
index 2f938dad8..0866e9a50 100644
--- a/src/renderer/Metal.zig
+++ b/src/renderer/Metal.zig
@@ -137,6 +137,11 @@ pub const CustomShaderState = struct {
     screen_texture: objc.Object, // MTLTexture
     sampler: mtl_sampler.Sampler,
     uniforms: mtl_shaders.PostUniforms,
+    /// The first time a frame was drawn. This is used to update the time
+    /// uniform.
+    first_frame_time: std.time.Instant,
+    /// The last time a frame was drawn. This is used to update the time
+    /// uniform.
     last_frame_time: std.time.Instant,
 
     pub fn deinit(self: *CustomShaderState) void {
@@ -412,6 +417,7 @@ pub fn init(alloc: Allocator, options: renderer.Options) !Metal {
                 .sample_rate = 1,
             },
 
+            .first_frame_time = try std.time.Instant.now(),
             .last_frame_time = try std.time.Instant.now(),
         };
     };
@@ -757,10 +763,12 @@ pub fn drawFrame(self: *Metal, surface: *apprt.Surface) !void {
 
     // If we have custom shaders, update the animation time.
     if (self.custom_shader_state) |*state| {
-        const now = std.time.Instant.now() catch state.last_frame_time;
-        const since_ns: f32 = @floatFromInt(now.since(state.last_frame_time));
+        const now = std.time.Instant.now() catch state.first_frame_time;
+        const since_ns: f32 = @floatFromInt(now.since(state.first_frame_time));
+        const delta_ns: f32 = @floatFromInt(now.since(state.last_frame_time));
         state.uniforms.time = since_ns / std.time.ns_per_s;
-        state.uniforms.time_delta = since_ns / std.time.ns_per_s;
+        state.uniforms.time_delta = delta_ns / std.time.ns_per_s;
+        state.last_frame_time = now;
     }
 
     // @autoreleasepool {}
diff --git a/src/renderer/opengl/custom.zig b/src/renderer/opengl/custom.zig
index c14ba3c5c..c988b62d0 100644
--- a/src/renderer/opengl/custom.zig
+++ b/src/renderer/opengl/custom.zig
@@ -45,10 +45,14 @@ pub const State = struct {
     /// The set of programs for the custom shaders.
     programs: []const Program,
 
-    /// The last time the frame was drawn. This is used to update
+    /// The first time a frame was drawn. This is used to update
     /// the time uniform.
     first_frame_time: std.time.Instant,
 
+    /// The last time a frame was drawn. This is used to update
+    /// the time uniform.
+    last_frame_time: std.time.Instant,
+
     pub fn init(
         alloc: Allocator,
         srcs: []const [:0]const u8,
@@ -136,6 +140,7 @@ pub const State = struct {
             .ebo = ebo,
             .fb_texture = fb_tex,
             .first_frame_time = try std.time.Instant.now(),
+            .last_frame_time = try std.time.Instant.now(),
         };
     }
 
@@ -180,8 +185,10 @@ pub const State = struct {
         // Update our frame time
         const now = std.time.Instant.now() catch self.first_frame_time;
         const since_ns: f32 = @floatFromInt(now.since(self.first_frame_time));
+        const delta_ns: f32 = @floatFromInt(now.since(self.last_frame_time));
         self.uniforms.time = since_ns / std.time.ns_per_s;
-        self.uniforms.time_delta = since_ns / std.time.ns_per_s;
+        self.uniforms.time_delta = delta_ns / std.time.ns_per_s;
+        self.last_frame_time = now;
 
         // Sync our uniform changes
         try self.syncUniforms();