Fix some errors in iso->pix->iso conversions, add debugging

Maps now render a bit more properly, and our mouse position can be
correctly assigned to a cell. Kind of, mostly.

cmd/view-map/main.go

@@ -51,8 +51,6 @@ func main() {
 		log.Fatal("Couldn't create window: %v", err)
 	}
 
-	// TODO: click to view cell data
-
 	win.OnKeyUp(ebiten.KeyLeft, env.changeOrigin(-64, +0))
 	win.OnKeyUp(ebiten.KeyRight, env.changeOrigin(+64, +0))
 	win.OnKeyUp(ebiten.KeyUp, env.changeOrigin(+0, -64))
@@ -62,6 +60,8 @@ func main() {
 		win.OnKeyUp(ebiten.Key1+ebiten.Key(i), env.setZIdx(i))
 	}
 
+	win.OnMouseClick(env.showCellData)
+
 	if err := win.Run(); err != nil {
 		log.Fatal(err)
 	}
@@ -87,3 +87,14 @@ func (e *env) setZIdx(to int) func() {
 		e.scenario.ZIdx = to
 	}
 }
+
+func (e *env) showCellData() {
+	screenX, screenY := ebiten.CursorPosition()
+	viewX, viewY := e.scenario.Viewpoint.X+screenX, e.scenario.Viewpoint.Y+screenY
+
+	log.Printf("Click registered at (%d,%d) screen, (%d,%d) virtual", screenX, screenY, viewX, viewY)
+
+	cell, pos := e.scenario.CellAtCursor()
+	log.Printf("Viewpoint: %#+v z=%v", e.scenario.Viewpoint, e.scenario.ZIdx)
+	log.Printf("Cell under cursor: (%.2f,%.2f,%d): %#+v", pos.X, pos.Y, pos.Z, cell)
+}