https://gfycat.com/weakthirdeasteuropeanshepherd

Instructions:

• Press Enter to create rectangles. You can select a single rectangle to move it or resize it.
• Press Ctrl + Z to undo.
• Press Ctrl + Shift + Z to redo.
• Press F4 to start a flood.
• Press F3 to clear the flood.
• Press F2 to reset the dropped frames counter.
• Press F1 to spawn 10k rectangles randomly. (It's best to zoom out so there are holes for the flood to fill.)
• Scroll the mouse wheel to zoom in or out.
• Press and hold the middle mouse button to pan the view.
• Press and hold the left mouse button to select rectangles.
• Press and hold the right mouse button to draw.

Source: https://github.com/Apostolique/FloodSimulator