diff --git a/roo_e/src/gui/wmwindow.c b/roo_e/src/gui/wmwindow.c
index e8cba0b..82fe6cb 100644
--- a/roo_e/src/gui/wmwindow.c
+++ b/roo_e/src/gui/wmwindow.c
@@ -28,6 +28,12 @@
 #include "font.h"
 
 
+typedef struct DamageListS {
+	RectT     rect;
+	SurfaceT *surface;
+} DamageListT;
+
+
 uint8_t  __MAGIC_WINDOW = 0;
 
 
@@ -666,6 +672,8 @@ void wmStartup(void) {
 
 void wmUpdate(EventT *event) {
 	int16_t              i;
+	int16_t              j;
+	int16_t              k;
 	PointT               widgetLocal;
 	int16_t              x2;
 	int16_t              y2;
@@ -673,6 +681,12 @@ void wmUpdate(EventT *event) {
 	WidgetT             *widget;
 	WidgetT             *widgetOver   = NULL;
 	WindowT             *win          = NULL;
+	WindowT             *win2         = NULL;
+	RectT               *rect;
+	RectT              **rects        = NULL;
+	DamageListT        **damageList   = NULL;
+	DamageListT         *damageItem   = NULL;
+	uint8_t              found;
 	ClickRawInputT       rawEvent     = { 0 };
 	static uint8_t       resizing     = 0;
 	static PointT        resizeOffset = { 0 };
@@ -915,6 +929,159 @@ void wmUpdate(EventT *event) {
 			break;
 		} // Left button processing.
 
+
+		// Calculate visible rectangle list.
+		//
+		// Start with the top window and divide it into smaller rectangles
+		// using the edges of every other window.  Add these to the "damage
+		// list".
+		//
+		// Then iterate through the remaining windows from top to bottom
+		// dividing them with the edges of every other window.  When finished
+		// with each window, compare the list of new rectangles to the existing
+		// damage list.  Add any rectangles that are not already there.
+		//
+		// Finally do the same as the remaining windows with the entire screen.
+
+		// Iterate over all windows, top to bottom.
+		for (i=0; i<=arrlen(_windowList); i++) {
+
+			// New rectangle.
+			NEW(RectT, rect);
+
+			// Are we comparing the desktop?
+			if (i == arrlen(_windowList)) {
+				// Yes.  Fake a window.
+				win      = NULL;
+				rect->x  = 0;
+				rect->y  = 0;
+				rect->x2 = videoDisplayWidthGet()  - 1;
+				rect->y2 = videoDisplayHeightGet() - 1;
+			} else {
+				// Get this window.
+				win      = (WindowT *)_windowList[i];
+				rect->x  = win->base.r.x;
+				rect->y  = win->base.r.y;
+				rect->x2 = win->base.r.x + win->base.r.w - 1;
+				rect->y2 = win->base.r.y + win->base.r.h - 1;
+			}
+
+			// Add this window to the rectangle list.
+			arrput(rects, rect);
+
+			// Iterate over all the other windows.
+			for (j=0; j<arrlen(_windowList); j++) {
+				win2 = (WindowT *)_windowList[j];
+				if (win != win2) {
+
+					// Get win2 extents.
+					x2 = win2->base.r.x + win2->base.r.w - 1;
+					y2 = win2->base.r.y + win2->base.r.h - 1;
+
+					// Check the edges of this window against all the
+					// rectangles in the current rectangle list.  Split
+					// and create new rectangles on any lines that intersect.
+					for (k=0; k<arrlen(rects); k++) {
+						// Compare Window Top
+						if ((win2->base.r.y > rects[k]->y) && (win2->base.r.y < rects[k]->y2)) {
+							NEW(RectT, rect);
+							rect->x  = rects[k]->x;
+							rect->x2 = rects[k]->x2;
+							rect->y2 = rects[k]->y2;
+							rects[k]->y2 = win2->base.r.y;
+							rect->y = win2->base.r.y;
+							arrput(rects, rect);
+						}
+						// Compare Window Bottom
+						if ((y2 > rects[k]->y) && (y2 < rects[k]->y2)) {
+							NEW(RectT, rect);
+							rect->x  = rects[k]->x;
+							rect->x2 = rects[k]->x2;
+							rect->y2 = rects[k]->y2;
+							rects[k]->y2 = y2;
+							rect->y = y2;
+							arrput(rects, rect);
+						}
+						// Compare Window Left
+						if ((win2->base.r.x > rects[k]->x) && (win2->base.r.x < rects[k]->x2)) {
+							NEW(RectT, rect);
+							rect->y  = rects[k]->y;
+							rect->x2 = rects[k]->x2;
+							rect->y2 = rects[k]->y2;
+							rects[k]->x2 = win2->base.r.x;
+							rect->x = win2->base.r.x;
+							arrput(rects, rect);
+						}
+						// Compare Window Right
+						if ((x2 > rects[k]->x) && (x2 < rects[k]->x2)) {
+							NEW(RectT, rect);
+							rect->y  = rects[k]->y;
+							rect->x2 = rects[k]->x2;
+							rect->y2 = rects[k]->y2;
+							rects[k]->x2 = x2;
+							rect->x = x2;
+							arrput(rects, rect);
+						}
+					}
+
+				}
+			}
+
+			// Add rectangles to the damage list.  Clear rectangle list.
+			while (arrlen(rects) > 0) {
+				found = 0;
+				// Is this the top window?
+				if (i != 0) {
+					// No.  Compare rectangles to existing damage list.
+					for (k=0; k<arrlen(damageList); k++) {
+						if ((rects[0]->x  == damageList[k]->rect.x ) &&
+							(rects[0]->y  == damageList[k]->rect.y ) &&
+							(rects[0]->x2 == damageList[k]->rect.x2) &&
+							(rects[0]->y2 == damageList[k]->rect.y2)) {
+							// We already have this.  Skip it.
+							found = 1;
+							break;
+						}
+					}
+				}
+
+				// Do we have this section of the screen yet?
+				if (!found) {
+					// Nope!  Add it.
+					NEW(DamageListT, damageItem);
+					//memcpy(&damageItem->rect, &rects[0], sizeof(RectT));
+					damageItem->rect.x  = rects[0]->x;
+					damageItem->rect.y  = rects[0]->y;
+					damageItem->rect.x2 = rects[0]->x2;
+					damageItem->rect.y2 = rects[0]->y2;
+					if (win != NULL) {
+						damageItem->surface = win->cached;
+					} else {
+						damageItem->surface = NULL;
+					}
+					arrput(damageList, damageItem);
+				}
+
+				// Delete this rect.
+				DEL(rects[0]);
+				arrdel(rects, 0);
+			}
+			arrfree(rects);
+
+			//***DEBUG*** Draw the damage list.
+			surfaceSet(__guiBackBuffer);
+			for (k=0; k<arrlen(damageList); k++) {
+				surfaceBox(damageList[k]->rect.x, damageList[k]->rect.y, damageList[k]->rect.x2, damageList[k]->rect.y2, GUI_RED);
+			}
+
+			// Delete damage list.
+			while (arrlen(damageList) > 0) {
+				DEL(damageList[0]);
+				arrdel(damageList, 0);
+			}
+			arrfree(damageList);
+		}
+
 	} // Do we have windows?
 }