diff --git a/src/gui/mainwindow.py b/src/gui/mainwindow.py
new file mode 100644
--- /dev/null
+++ b/src/gui/mainwindow.py
@@ -0,0 +1,115 @@
+import logging as log
+import tkinter as tk
+
+import PIL
+from PIL import ImageTk
+
+import config
+import imageanalyzer
+from corners import Corners
+from epoint import EPoint
+from grid import Grid
+from .boardview import BoardView
+
+
+class MainWindow(tk.Frame):
+	def __init__(self,parent,master=None):
+		self.parent=parent
+		self.corners=Corners()
+
+		self.currentFrame=None
+		self._boardGrid=None
+
+		self.img=None
+		self._imgSizeCoef=1
+		self._imgShift=EPoint(0,0)
+
+		tk.Frame.__init__(self, master)
+		self.grid(column=0,row=0)
+		self._createWidgets()
+
+	def setCurrentFrame(self,frame):
+		self.currentFrame=frame
+
+		w=int(self.imgView['width'])
+		h=int(self.imgView['height'])
+		self.img=ImageTk.PhotoImage(frame.resize((w,h),resample=PIL.Image.BILINEAR))
+
+		wo,ho=self.currentFrame.size # o for original
+		widthRatio=wo/w
+		heightRatio=ho/h
+		self._imgSizeCoef=max(widthRatio,heightRatio)
+		# shift compensates possible horizontal or vertical empty margins from unmatching aspect ratios
+		self._imgShift=EPoint(wo-w*self._imgSizeCoef,ho-h*self._imgSizeCoef)/2
+
+	def _createWidgets(self):
+		# a captured frame with overlay graphics
+		self.imgView=tk.Canvas(self)
+		self.imgView.configure(width=480,height=360)
+
+		self.imgView.bind('<1>',lambda e: self.addCorner(e.x,e.y))
+
+		self.imgView.grid(column=0,row=0)
+
+		# board with detected stones
+		self.boardView= BoardView(self)
+		self.boardView.grid(column=1,row=0)
+
+		# more controls below the board
+		self.scaleTresB=tk.Scale(self, orient=tk.HORIZONTAL, length=200, from_=0.0, to=100.0, command=self.refreshTresholds)
+		self.scaleTresW=tk.Scale(self, orient=tk.HORIZONTAL, length=200, from_=0.0, to=100.0, command=self.refreshTresholds)
+		self.scaleTresB.set(30.0) # !! proper defaults
+		self.scaleTresW.set(60.0)
+		self.scaleTresB.grid(column=0,row=1,columnspan=2)
+		self.scaleTresW.grid(column=0,row=2,columnspan=2)
+
+		# render everything
+		self.redrawImgView()
+
+	## Stores a grid corner located at x,y coordinates.
+	def addCorner(self,x,y):
+		self.corners.add(x,y)
+		if self.corners.canonizeOrder():
+			# transform corners from show coordinates to real coordinates
+			log.debug(self.corners.corners)
+			self._boardGrid=Grid(self.corners.corners)
+			corners=[(c*self._imgSizeCoef+self._imgShift) for c in self.corners.corners]
+			self.parent.sendMsg("setCorners",(corners,))
+
+		self.redrawImgView()
+
+	## Redraws the current image and its overlay.
+	def redrawImgView(self):
+		if self.currentFrame and self.img:
+			self.imgView.create_image(2,2,anchor="nw",image=self.img)
+
+		for corner in self.corners.corners:
+			self.markPoint(corner.x,corner.y)
+
+		if self._boardGrid!=None and config.gui.showGrid:
+			for r in range(19):
+				a=self._boardGrid.intersections[r][0]
+				b=self._boardGrid.intersections[r][-1]
+				self.imgView.create_line(a.x,a.y,b.x,b.y,fill='#00ff00')
+			for c in range(19):
+				a=self._boardGrid.intersections[0][c]
+				b=self._boardGrid.intersections[-1][c]
+				self.imgView.create_line(a.x,a.y,b.x,b.y,fill='#00ff00')
+
+		if self._boardGrid!=None and config.gui.showBigPoints:
+			for r in range(19):
+				for c in range(19):
+					((r1,c1),(r2,c2))=imageanalyzer.relevantRect(self._boardGrid.intersections[r][c], *(self._boardGrid.stoneSizeAt(r, c)))
+					self.imgView.create_rectangle(r1,c1,r2,c2,outline="#00ffff")
+
+		self.imgView.grid()
+
+	## Marks a point at the image with a green cross. Used for corners.
+	def markPoint(self,x,y):
+		self.imgView.create_line(x-3,y-3,x+4,y+4,fill="#00ff00")
+		self.imgView.create_line(x-3,y+3,x+4,y-4,fill="#00ff00")
+
+		self.imgView.grid()
+
+	def refreshTresholds(self,_):
+		self.parent.sendMsg("setTresholds",tuple(),{"tresB":self.scaleTresB.get(), "tresW":self.scaleTresW.get()})