PaintTool SAI includes tools for making boxes filled with colors or for drawing the outline of a box or other shape on your image. Unlike some other graphics-editing programs, PaintTool SAI doesn't include a list of predefined shapes you can draw on your image. Use the Selection tool in combination with the Bucket tool to create a filled box or use the Line tool on the a linework layer to draw the outline of a box on your image. The Bucket tool is only available on a normal layer, while the Line tool is only available on a linework layer.
Filled Box
Step 1
Click the "Selection" tool under the color wheel. The Selection tool appears as a square icon with dashed lines.
Step 2
Place the mouse cursor over a point on the image for one of the box's corners.
Step 3
Left-click on the image, hold down the mouse button and move the mouse cursor to draw the box.
Step 4
Release the mouse button to select the box's outline.
Step 5
Select a color to fill the box with by clicking it on the color wheel.
Step 6
Click the "Bucket" tool in the toolbox under the color wheel. Select a normal layer from the layer box at the left side of the window if you don't see the Bucket tool icon.
Step 7
Move the mouse cursor to the inside of your box selection and click once to fill the box with your selected color.
Outline
Step 1
Click the "Layer" menu at the top of the PaintTool SAI window and select "New Linework Layer." If you already have a linework layer, you can select it from the layer box at the left side of the window.
Step 2
Select a color for the outline from the color wheel near the top of the window.
Step 3
Click the "Line" tool in the toolbox below the color wheel.
Step 4
Position your mouse cursor at a location for one of the box's corners in the image and click once to start drawing a line from this location.
Step 5
Move the mouse cursor to a location for an adjacent corner. A preview of the line appears on the image; click once to place the line.
Step 6
Continue drawing the box by clicking at all four corners. Double-click on the last corner to stop drawing the shape.