added a package to create a simple window with a canvas using SDL

sdlcanvas/sdlcanvas.go

@@ -0,0 +1,114 @@
+package sdlcanvas
+
+import (
+	"fmt"
+	_ "image/gif"
+	_ "image/jpeg"
+	_ "image/png"
+	"log"
+	"runtime"
+	"time"
+
+	"github.com/go-gl/gl/v3.2-core/gl"
+	"github.com/veandco/go-sdl2/sdl"
+
+	"tests/canvas"
+	"tests/canvas/goglimpl"
+)
+
+type Window struct {
+	Window    *sdl.Window
+	GLContext sdl.GLContext
+}
+
+func CreateCanvasWindow(w, h int, title string) (*Window, *canvas.Canvas, error) {
+	runtime.LockOSThread()
+
+	// init SDL
+	err := sdl.Init(sdl.INIT_VIDEO)
+	if err != nil {
+		return nil, nil, fmt.Errorf("Error initializing SDL: %v", err)
+	}
+
+	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, 1)
+	sdl.GL_SetAttribute(sdl.GL_DOUBLEBUFFER, 1)
+	sdl.GL_SetAttribute(sdl.GL_MULTISAMPLEBUFFERS, 1)
+	sdl.GL_SetAttribute(sdl.GL_MULTISAMPLESAMPLES, 4)
+
+	// create window
+	window, err := sdl.CreateWindow(title, sdl.WINDOWPOS_CENTERED, sdl.WINDOWPOS_CENTERED, w, h, sdl.WINDOW_RESIZABLE|sdl.WINDOW_OPENGL)
+	if err != nil {
+		return nil, nil, fmt.Errorf("Error creating window: %v", err)
+	}
+
+	// create GL context
+	glContext, err := sdl.GL_CreateContext(window)
+	if err != nil {
+		return nil, nil, fmt.Errorf("Error creating GL context: %v", err)
+	}
+
+	// init GL
+	err = gl.Init()
+	if err != nil {
+		return nil, nil, fmt.Errorf("Error initializing GL: %v", err)
+	}
+
+	sdl.GL_SetSwapInterval(0)
+	gl.Enable(gl.MULTISAMPLE)
+
+	err = canvas.LoadGL(goglimpl.GLImpl{})
+	if err != nil {
+		return nil, nil, fmt.Errorf("Error loading canvas GL assets: %v", err)
+	}
+
+	cv := canvas.New(0, 0, w, h)
+	wnd := &Window{
+		Window:    window,
+		GLContext: glContext,
+	}
+
+	return wnd, cv, nil
+}
+
+func (wnd *Window) Destroy() {
+	sdl.GL_DeleteContext(wnd.GLContext)
+	wnd.Window.Destroy()
+}
+
+func (wnd *Window) MainLoop(drawFunc func()) {
+	// main loop
+	for running := true; running; {
+		for {
+			ei := sdl.PollEvent()
+			if ei == nil {
+				break
+			}
+			switch e := ei.(type) {
+			case *sdl.WindowEvent:
+				if e.Event == sdl.WINDOWEVENT_CLOSE {
+					running = false
+				}
+			case *sdl.KeyDownEvent:
+				if e.Keysym.Scancode == sdl.SCANCODE_ESCAPE {
+					running = false
+				}
+			}
+		}
+
+		err := sdl.GL_MakeCurrent(wnd.Window, wnd.GLContext)
+		if err != nil {
+			log.Println(err)
+			time.Sleep(10 * time.Millisecond)
+			continue
+		}
+
+		drawFunc()
+
+		sdl.GL_SwapWindow(wnd.Window)
+	}
+}