First pass at custom cursor display

internal/ui/window.go

@@ -3,6 +3,7 @@ package ui
 import (
 	"flag"
 	"fmt"
+	"image"
 	"log"
 	"os"
 	"runtime/debug"
@@ -23,11 +24,16 @@ var (
 	cpuprofile  = flag.String("cpuprofile", "", "write cpu profile to `file`")
 )
 
+// TODO: move all scaling into Window, so drivers only need to cope with one
+// coordinate space. This will allow us to draw custom mouse cursors in the
+// window, rather than in the driver.
 type Window struct {
 	Title             string
 	KeyUpHandlers     map[ebiten.Key]func()
 	MouseWheelHandler func(float64, float64)
 
+	cursor *ebiten.Image
+
 	// Allow the "game" to be switched out at any time
 	game Game
 
@@ -68,6 +74,17 @@ func (w *Window) Layout(_, _ int) (int, int) {
 	return w.xRes, w.yRes
 }
 
+func (w *Window) SetCursor(cursor *ebiten.Image) {
+	w.cursor = cursor
+
+	// Hide the system cursor if we have a custom one
+	if cursor == nil {
+		ebiten.SetCursorMode(ebiten.CursorModeVisible)
+	} else {
+		ebiten.SetCursorMode(ebiten.CursorModeHidden)
+	}
+}
+
 func (w *Window) Update(screen *ebiten.Image) (outErr error) {
 	// Ebiten does not like it if we panic inside its main loop
 	defer func() {
@@ -108,6 +125,16 @@ func (w *Window) Update(screen *ebiten.Image) (outErr error) {
 		return err
 	}
 
+	if w.cursor != nil {
+		// TODO: account for scaling, including the hotspot.
+		pos := image.Pt(ebiten.CursorPosition())
+		op := ebiten.DrawImageOptions{}
+		op.GeoM.Translate(float64(pos.X), float64(pos.Y))
+		if err := screen.DrawImage(w.cursor, &op); err != nil {
+			return err
+		}
+	}
+
 	if w.debug {
 		// Draw FPS, etc, to the screen
 		msg := fmt.Sprintf("tps=%0.2f fps=%0.2f", ebiten.CurrentTPS(), ebiten.CurrentFPS())