Adding support for manipulating cursors (#114)

Adding support for manipulating cursors

backends/opengl/cursor.go

@@ -0,0 +1,49 @@
+package opengl
+
+import (
+	"image"
+	"runtime"
+
+	"github.com/go-gl/glfw/v3.3/glfw"
+	"github.com/gopxl/mainthread/v2"
+	"github.com/gopxl/pixel/v2"
+)
+
+type StandardCursor int
+
+const (
+	ArrowCursor     = StandardCursor(glfw.ArrowCursor)
+	IBeamCursor     = StandardCursor(glfw.IBeamCursor)
+	CrosshairCursor = StandardCursor(glfw.CrosshairCursor)
+	HandCursor      = StandardCursor(glfw.HandCursor)
+	HResizeCursor   = StandardCursor(glfw.HResizeCursor)
+	VResizeCursor   = StandardCursor(glfw.VResizeCursor)
+)
+
+type Cursor = glfw.Cursor
+
+// CreateStandardCursor creates a new standard cursor.
+func CreateStandardCursor(cursorId StandardCursor) *Cursor {
+	c := mainthread.CallVal(func() *Cursor {
+		return glfw.CreateStandardCursor(glfw.StandardCursor(cursorId))
+	})
+	runtime.SetFinalizer(c, (*Cursor).Destroy)
+	return c
+}
+
+// CreateCursorImage creates a new cursor from an image with the specified hotspot (where the click is registered).
+func CreateCursorImage(img image.Image, hot pixel.Vec) *Cursor {
+	c := mainthread.CallVal(func() *Cursor {
+		return glfw.CreateCursor(img, int(hot.X), int(hot.Y))
+	})
+	runtime.SetFinalizer(c, (*Cursor).Destroy)
+	return c
+}
+
+// SetCursor sets the cursor for the window.
+func (w *Window) SetCursor(cursor *Cursor) {
+	mainthread.Call(func() {
+		w.window.SetCursor(cursor)
+		w.cursor = cursor
+	})
+}

backends/opengl/window.go

@@ -109,6 +109,7 @@ type Window struct {
 	mouseEnteredCallback func(win *Window, entered bool)
 	mouseMovedCallback   func(win *Window, pos pixel.Vec)
 	scrollCallback       func(win *Window, scroll pixel.Vec)
+	cursor               *Cursor
 }
 
 var currWin *Window
@@ -204,6 +205,9 @@ func NewWindow(cfg WindowConfig) (*Window, error) {
 		})
 	}
 
+	w.cursor = CreateStandardCursor(ArrowCursor)
+	w.SetCursor(w.cursor)
+
 	w.SetVSync(cfg.VSync)
 
 	w.initInput()
@@ -226,6 +230,7 @@ func (w *Window) Destroy() {
 
 // Update swaps buffers and polls events. Call this method at the end of each frame.
 func (w *Window) Update() {
+	w.SetCursor(w.cursor)
 	w.SwapBuffers()
 	w.UpdateInput()
 }