diff --git a/CMakeLists.txt b/CMakeLists.txt
index e03208b..49b9d4b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -106,6 +106,7 @@ set(sources_pcmockup
     pcmockup/debugwindowset.c
     pcmockup/windowcontainer.c
     pcmockup/imagewindow.c
+    pcmockup/windowgrid.c
 )
 assign_source_group(${sources_pcmockup})
 
diff --git a/pcmockup/imagewindow.c b/pcmockup/imagewindow.c
index 3118428..689a045 100644
--- a/pcmockup/imagewindow.c
+++ b/pcmockup/imagewindow.c
@@ -11,6 +11,7 @@ struct ImageWindow
     float aspect;
     SDL_Rect lastContentPos;
     bool isOpen, isEssential;
+    ImVec2 initialPosition;
 };
 
 ImageWindow* imageWindow_init(const char* title, GSize initialSize, bool_t isEssential)
@@ -48,6 +49,7 @@ ImageWindow* imageWindow_init(const char* title, GSize initialSize, bool_t isEss
     me->isEssential = isEssential;
     me->windowSize = initialSize;
     me->aspect = (float)initialSize.w / initialSize.h;
+    me->initialPosition.x = -1; // undefined initial position
     return me;
 }
 
@@ -95,6 +97,8 @@ void imageWindow_update(ImageWindow* me)
         ? NULL // essential windows don't get a close button
         : &me->isOpen;
 
+    if (me->initialPosition.x >= 0 && me->initialPosition.y >= 0)
+        igSetNextWindowPos(me->initialPosition, ImGuiCond_Once, zero);
     igSetNextWindowContentSize(size);
     igPushStyleVarVec2(ImGuiStyleVar_WindowPadding, zero);  // space between image and window border
     igPushStyleVarVec2(ImGuiStyleVar_ItemSpacing, zero);    // space between vertical centering dummy and image
@@ -122,6 +126,14 @@ void imageWindow_update(ImageWindow* me)
     };
 }
 
+void imageWindow_setInitialPosition(ImageWindow* me, GPoint initialPosition)
+{
+    me->initialPosition = (ImVec2) {
+        (float)initialPosition.x,
+        (float)initialPosition.y
+    };
+}
+
 void imageWindow_toggle(ImageWindow* me, bool_t isOpen)
 {
     me->isOpen = isOpen;
diff --git a/pcmockup/pcmockup.h b/pcmockup/pcmockup.h
index da81694..3127982 100644
--- a/pcmockup/pcmockup.h
+++ b/pcmockup/pcmockup.h
@@ -20,6 +20,7 @@ void imageWindow_free(ImageWindow* me);
 void imageWindow_setImageData(ImageWindow* me, GSize size, const SDL_Color* data);
 SDL_Rect imageWindow_getContentPos(ImageWindow* me); // in screen coordinates
 void imageWindow_update(ImageWindow* me);
+void imageWindow_setInitialPosition(ImageWindow* me, GPoint initialPosition);
 void imageWindow_toggle(ImageWindow* me, bool_t isOpen);
 bool_t imageWindow_isOpen(ImageWindow* me);
 
@@ -46,6 +47,9 @@ void debugWindowSet_update(DebugWindowSet* set);
 void debugWindowSet_updateMenubar(DebugWindowSet* set);
 void debugWindowSet_handleUpdate(DebugWindowSet* set, const SDL_Event* ev);
 
+GSize windowGrid_getSingleSize(int nWindows, GSize totalSize);
+GPoint windowGrid_getSinglePos(int nWindows, GSize totalSize, int windowI);
+
 typedef struct PCMockup PCMockup;
 PCMockup* pcmockup_init();
 void pcmockup_free(PCMockup* me);
diff --git a/pcmockup/windowgrid.c b/pcmockup/windowgrid.c
new file mode 100644
index 0000000..e69de29