added an example for using SDL directly

examples/sdl/sdl.go

@@ -0,0 +1,117 @@
+package main
+
+import (
+	"log"
+	"runtime"
+	"time"
+
+	"github.com/go-gl/gl/v3.2-core/gl"
+	"github.com/tfriedel6/canvas"
+	"github.com/tfriedel6/canvas/goglimpl"
+	"github.com/veandco/go-sdl2/sdl"
+)
+
+func main() {
+	runtime.LockOSThread()
+
+	// init SDL
+	err := sdl.Init(sdl.INIT_VIDEO)
+	if err != nil {
+		log.Fatalf("Error initializing SDL: %v", err)
+	}
+	defer sdl.Quit()
+
+	// the stencil size setting is required for the canvas to work
+	sdl.GL_SetAttribute(sdl.GL_RED_SIZE, 8)
+	sdl.GL_SetAttribute(sdl.GL_GREEN_SIZE, 8)
+	sdl.GL_SetAttribute(sdl.GL_BLUE_SIZE, 8)
+	sdl.GL_SetAttribute(sdl.GL_ALPHA_SIZE, 8)
+	sdl.GL_SetAttribute(sdl.GL_DEPTH_SIZE, 0)
+	sdl.GL_SetAttribute(sdl.GL_STENCIL_SIZE, 8)
+	sdl.GL_SetAttribute(sdl.GL_DOUBLEBUFFER, 1)
+	sdl.GL_SetAttribute(sdl.GL_MULTISAMPLEBUFFERS, 1)
+	sdl.GL_SetAttribute(sdl.GL_MULTISAMPLESAMPLES, 4)
+
+	// create window
+	const title = "SDL Test"
+	window, err := sdl.CreateWindow(title, sdl.WINDOWPOS_CENTERED, sdl.WINDOWPOS_CENTERED, 1280, 720, sdl.WINDOW_RESIZABLE|sdl.WINDOW_OPENGL)
+	if err != nil {
+		// fallback in case multisample is not available
+		sdl.GL_SetAttribute(sdl.GL_MULTISAMPLEBUFFERS, 0)
+		sdl.GL_SetAttribute(sdl.GL_MULTISAMPLESAMPLES, 0)
+		window, err = sdl.CreateWindow(title, sdl.WINDOWPOS_CENTERED, sdl.WINDOWPOS_CENTERED, 1280, 720, sdl.WINDOW_RESIZABLE|sdl.WINDOW_OPENGL)
+		if err != nil {
+			log.Fatalf("Error creating window: %v", err)
+		}
+	}
+	defer window.Destroy()
+
+	// create GL context
+	glContext, err := sdl.GL_CreateContext(window)
+	if err != nil {
+		log.Fatalf("Error creating GL context: %v", err)
+	}
+
+	// init GL
+	err = gl.Init()
+	if err != nil {
+		log.Fatalf("Error initializing GL: %v", err)
+	}
+
+	// enable vsync and multisample (if available)
+	sdl.GL_SetSwapInterval(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 running := true; running; {
+		err := sdl.GL_MakeCurrent(window, glContext)
+		if err != nil {
+			time.Sleep(10 * time.Millisecond)
+			continue
+		}
+
+		// handle events
+		for {
+			event := sdl.PollEvent()
+			if event == nil {
+				break
+			}
+
+			switch e := event.(type) {
+			case *sdl.KeyDownEvent:
+				if e.Keysym.Scancode == sdl.SCANCODE_ESCAPE {
+					running = false
+				}
+			case *sdl.WindowEvent:
+				if e.Type == sdl.WINDOWEVENT_CLOSE {
+					running = false
+				}
+			}
+		}
+
+		// 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
+		sdl.GL_SwapWindow(window)
+	}
+}
+
+func run(cv *canvas.Canvas, w, h float64) {
+	cv.SetFillStyle("#000")
+	cv.FillRect(0, 0, w, h)
+	cv.SetFillStyle("#0F0")
+	cv.FillRect(w*0.25, h*0.25, w*0.5, h*0.5)
+}