added an example for using GLFW

examples/glfw/glfw.go

@@ -0,0 +1,74 @@
+package main
+
+import (
+	"log"
+	"runtime"
+
+	"github.com/go-gl/gl/v3.2-core/gl"
+	"github.com/go-gl/glfw/v3.2/glfw"
+	"github.com/tfriedel6/canvas"
+	"github.com/tfriedel6/canvas/goglimpl"
+)
+
+func main() {
+	runtime.LockOSThread()
+
+	// init SDL
+	err := glfw.Init()
+	if err != nil {
+		log.Fatalf("Error initializing GLFW: %v", err)
+	}
+	defer glfw.Terminate()
+
+	// the stencil size setting is required for the canvas to work
+	glfw.WindowHint(glfw.StencilBits, 8)
+	glfw.WindowHint(glfw.DepthBits, 0)
+
+	// create window
+	window, err := glfw.CreateWindow(1280, 720, "GLFW Test", nil, nil)
+	if err != nil {
+		log.Fatalf("Error creating window: %v", err)
+	}
+	window.MakeContextCurrent()
+
+	// init GL
+	err = gl.Init()
+	if err != nil {
+		log.Fatalf("Error initializing GL: %v", err)
+	}
+
+	// set vsync on, enable multisample (if available)
+	glfw.SwapInterval(1)
+	gl.Enable(gl.MULTISAMPLE)
+
+	// load canvas GL assets
+	err = canvas.LoadGL(goglimpl.GLImpl{})
+	if err != nil {
+		log.Fatalf("Error loading canvas GL assets: %v", err)
+	}
+
+	// initialize canvas with zero size, since size is set in main loop
+	cv := canvas.New(0, 0, 0, 0)
+
+	for !window.ShouldClose() {
+		window.MakeContextCurrent()
+		glfw.PollEvents()
+
+		// set canvas size
+		ww, wh := window.GetSize()
+		cv.SetSize(ww, wh)
+
+		// call the run function to do all the drawing
+		run(cv, float64(ww), float64(wh))
+
+		// swap back and front buffer
+		window.SwapBuffers()
+	}
+}
+
+func run(cv *canvas.Canvas, w, h float64) {
+	cv.SetFillStyle("#000")
+	cv.FillRect(0, 0, w, h)
+	cv.SetFillStyle("#00F")
+	cv.FillRect(w*0.25, h*0.25, w*0.5, h*0.5)
+}