Show FPS when the F key is pressed.

1 files changed, 25 insertions, 1 deletions

diff --git a/pongo.go b/pongo.go
index 984bf58..122044d 100644
--- a/pongo.go
+++ b/pongo.go
@@ -196,6 +196,11 @@ func pong() error {
 	paddle1 := paddle{pos: screenHeight / 2, side: left}
 	paddle2 := paddle{pos: screenHeight / 2, side: right}
 
+	fpsTime := time.Duration(0)
+	frames := 0
+	fps := 0
+	showFPS := false
+
 	lastFrameTime := time.Now()
 	accumulator := time.Duration(0)
 
@@ -207,15 +212,21 @@ func pong() error {
 			case *sdl.QuitEvent:
 				return nil
 			case *sdl.KeyboardEvent:
+				if t.Type != sdl.KEYDOWN {
+					continue
+				}
 				switch t.Keysym.Sym {
 				case sdl.K_q, sdl.K_c, sdl.K_ESCAPE:
 					return nil
+				case sdl.K_f:
+					showFPS = !showFPS
 				}
 			}
 		}
 
-		accumulator += frameStart.Sub(lastFrameTime)
+		frameTime := frameStart.Sub(lastFrameTime)
 		lastFrameTime = frameStart
+		accumulator += frameTime
 
 		const simulationSpeed = time.Second / 120
 		for ; accumulator >= simulationSpeed; accumulator -= simulationSpeed {
@@ -313,6 +324,19 @@ func pong() error {
 			fmt.Fprintln(os.Stderr, err)
 		}
 
+		fpsTime += frameTime
+		frames++
+		if fpsTime >= 5*time.Second {
+			fps = (frames*int(time.Second) + int(fpsTime)/2) / int(fpsTime)
+			fpsTime = 0
+			frames = 0
+		}
+		if showFPS {
+			if err := drawNumber(renderer, fps, 0, 0); err != nil {
+				fmt.Fprintln(os.Stderr, err)
+			}
+		}
+
 		renderer.Present()
 	}
 	panic("unreachable")