Here are the different tools of the Viewport:
        
 
                    
                    
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                        2D-3D view
                        Switch 2D/3D view
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                        Show/Hide Rulers
                      
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                        Snap to pixels
                      
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                        Display helpers bound to Model/World
                      
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                        Show/Hide Helpers
                      
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                        Show/Hide Outlines
                      
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                        Show/Hide Wireframe
                      
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                        Set background to Transparent/Black/White
                      
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                        Choose the channel between Color and alpha, Color only, Luminance, Red, Green, Blue, Alpha or Depth pass
                      
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                        Zoom in/out, Fit to screen or Fit 1px:1px
                      
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                        Show/Hide Grid
                      
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                        Take a Preview Screenshot
                      
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                        Switch camera (when in a 3D space)
                      
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                        Navigation mode
                      
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                        Translate (shortcut: T)
                      
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                        Rotate (shortcut: R)
                      
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                        Scale (shortcut: T)
                      
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                        Edit Mode
                        Allow to edit quickly some layers parameters
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        There are two different viewport modes for a 
                    Compo
                    Composite 2D Layer, Shape layer and 3D Layer together. [Ctrl] + [Shift] + [N] to create a new composition after opening Smode
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                     adapted for 2D and for 3D.
        
                    
                      Post-effects are not applied in 3D mode to make the preview faster to compute
                    
                    Visualizer (Green arrow)
                              To visualize a specific element or a modifier of the composition, you can use the visualizer by clicking the green arrow by the side of each Layer, Mask and Modifier:
                    
 
                    
                    If you're using this tool on a mask or a modifier, you will see a split view with the layer before and after the mask modifier has been applied:
                    
 
                    
                     
                    
                    4 Splitted Views
                      Double-click on a 3D viewport to access the splitted view with a front, side, top, and a perspective view:
			  
 
                    
                      You can choose one of the preview modes by double-clicking on it.