added a simple event handling example

examples/events/events.go

@@ -0,0 +1,77 @@
+package main
+
+import (
+	"log"
+	"math"
+	"time"
+
+	"github.com/tfriedel6/canvas/sdlcanvas"
+)
+
+type circle struct {
+	x, y  float64
+	color string
+}
+
+func main() {
+	wnd, cv, err := sdlcanvas.CreateWindow(1280, 720, "Canvas Example")
+	if err != nil {
+		log.Println(err)
+		return
+	}
+	defer wnd.Destroy()
+
+	var mx, my, action float64
+	circles := make([]circle, 0, 100)
+
+	wnd.MouseMove = func(x, y int) {
+		mx, my = float64(x), float64(y)
+	}
+	wnd.MouseDown = func(button, x, y int) {
+		action = 1
+		circles = append(circles, circle{x: mx, y: my, color: "#F00"})
+	}
+	wnd.KeyDown = func(scancode int, rn rune, name string) {
+		switch name {
+		case "Escape":
+			wnd.Close()
+		case "Space":
+			action = 1
+			circles = append(circles, circle{x: mx, y: my, color: "#0F0"})
+		case "Enter":
+			action = 1
+			circles = append(circles, circle{x: mx, y: my, color: "#00F"})
+		}
+	}
+
+	lastTime := time.Now()
+
+	wnd.MainLoop(func() {
+		now := time.Now()
+		diff := now.Sub(lastTime)
+		lastTime = now
+		action -= diff.Seconds() * 3
+		action = math.Max(0, action)
+
+		w, h := float64(cv.Width()), float64(cv.Height())
+
+		// Clear the screen
+		cv.SetFillStyle("#000")
+		cv.FillRect(0, 0, w, h)
+
+		// Draw a circle around the cursor
+		cv.SetStrokeStyle("#F00")
+		cv.SetLineWidth(6)
+		cv.BeginPath()
+		cv.Arc(mx, my, 24+action*24, 0, math.Pi*2, false)
+		cv.Stroke()
+
+		// Draw circles where the user has clicked
+		for _, circle := range circles {
+			cv.SetFillStyle(circle.color)
+			cv.BeginPath()
+			cv.Arc(circle.x, circle.y, 24, 0, math.Pi*2, false)
+			cv.Fill()
+		}
+	})
+}