kernel: Add FPS tracking.

1 files changed, 18 insertions, 7 deletions

diff --git a/starling/kernel.scm b/starling/kernel.scm
index 193eb7b..25e92b6 100644
--- a/starling/kernel.scm
+++ b/starling/kernel.scm
@@ -52,9 +52,11 @@
             update-hz
             window
             gl-context
+            avg-frame-time
             current-kernel
             boot-kernel
             elapsed-time
+            fps
             current-scene
             push-scene
             pop-scene
@@ -75,6 +77,7 @@
   (window #:accessor window)
   (gl-context #:accessor gl-context)
   (default-viewport #:accessor default-viewport)
+  (avg-frame-time #:accessor avg-frame-time #:init-form 0.0)
   (controllers #:accessor controllers #:init-thunk make-hash-table)
   (repl #:accessor repl)
   ;; The scene stack.
@@ -208,13 +211,18 @@
   (gpu-reap!))
 
 (define-method (render* (kernel <kernel>) alpha)
-  ;; Switch to the null viewport to ensure that
-  ;; the default viewport will be re-applied and
-  ;; clear the screen.
-  (gpu-state-set! *viewport-state* null-viewport)
-  (with-viewport (default-viewport kernel)
-    (next-method))
-  (swap-gl-window (window kernel)))
+  (let ((start-time (elapsed-time)))
+    ;; Switch to the null viewport to ensure that
+    ;; the default viewport will be re-applied and
+    ;; clear the screen.
+    (gpu-state-set! *viewport-state* null-viewport)
+    (with-viewport (default-viewport kernel)
+      (next-method))
+    (swap-gl-window (window kernel))
+    ;; Compute FPS.
+    (set! (avg-frame-time kernel)
+          (+ (* (- (elapsed-time) start-time) 0.1)
+             (* (avg-frame-time kernel) 0.9)))))
 
 (define-method (on-error (kernel <kernel>) stack key args)
   (if (developer-mode? kernel)
@@ -227,6 +235,9 @@
 (define (elapsed-time)
   (sdl-ticks))
 
+(define-method (fps kernel)
+  (/ 1000.0 (avg-frame-time kernel)))
+
 (define-method (boot-kernel (kernel <kernel>) (scene <scene>))
   (sdl-init)
   ;; This will throw an error if any audio subsystem is unavailable,