The latest version of this document can be found at www.broad.ology.org.uk/amiga/sketchblock/selectiontools.html

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SketchBlock 3.4 - Digital Sketching For The Amiga

Selection Tools

This set of tools allows to to create and edit a selection mask. This can be used to limit the area that other drawing operations can be applied to. The selection mask can have an alpha value allowing for smooth borders to selected areas. Selected areas can also be used to copy sections of a layer into the clipboard or a new layer.

There are currently 4 tools avaiable.

• Rectangle Selection (including squares)
• Elipitical Selection (include circles)
• Flood Select
• Colour Select

Common Selection Tool Settings




All four (and any future) selection tools settings have the selection mode buttons in common. These control the way the current selection mask is modified by the new selection created by the tool. There are 4 modes.

• Replace: The current mask is replaced by the newly defined area.
• Add: The newly defined are is added to the existing mask.
• Subtract: The newly defined area is subtracted or cut from the existing masked area
• Intersection: The newly defined area and existing mask are combined so that the result has only those pixels common to both mask areas
The 4 modes allow for complex shapes to be created by combineing relatively simple operations.

Rectangle Selection

The Rectangle Selection tool allows you to create rectangular and square selections. To perform a selection, initialy click and drag the mouse anywhere in the sketch window of the project you are editing. Then you can drag and reposition the edges, corners, or whole selection. The mouse pointer will change to indicate the current operation. Once you are happy with the selected area, you finalise the selection by pressing the space bar. The chosen operation from the 4 modes discussed above will then be performed.

Rectangle Selection Setting

As well as the 4 common mode buttons the rectangle selection displays the coordinates and size of the currently edited area. These gadgets are currently read only.

Below these is the check box to lock aspect. If this is checked then the initial selection will be square, but once unchecked a rectangle can be made, rechecking it allows you to resize this rectangle with a constant aspect.

Next is the "Reset" button, this resets the tool (not the oeveral selection mask) so that you can initialise another selection with a click and drag action

Eliptical Selection Tool

Use this tool to create eliptical or circular selections. It operation is very similar to the rectangtle select tool. You will see the gadgets in the setttings are very similar, the width and height refer to the containing box. Currently only elipses with the axes horizontal and vertical can be created. Again press the space bar to finalise the selection.

Flood Selection Tool

This is the equivalent to the familar flood tool found in programs like DPaint or PPaint. However there are some differences.

Clicking anywhere in the sketch window will progressively select all the contiguous pixels in a layer that share the colour of the pixel at the point clicked

Flood Select Settings

Again you will see the common 4 mode buttons, beneath these is a slider that controls the range of colour selected. The lower the value the more accurate the pixels flood selected must match in colour to the initial pixel, with 0 being an exact match. The next gadget enables soft selection. When this is selected the mask value for each pixel will depend on the accuracy of the match, with exact matches being 1.0 and no match being 0.0 this enable smooth antliased selected areas. This effect will be most noticable when working with a gradiant or radial fill.

Colour Selection Tool

This is very similar to the flood tool except that all pixels with the same colour as the pixel clicked on will be added to the selection. Again it has the range and soft select options.

Selection Menu Operations

As well as the tools available in the tools window there are a number of operations available from the menus.

• Edit Menu:
  • Clear Selection:
    This resets the selection mask completely removing any restrictions on drawing operations
  • Invert Selection:
    This flips the selection so that all selected pixels are now unselected and vice versa. Soft selected pixels will have value of 1.0 - previous value. eg old value 0.3 new value1.0 - 0.3 = 0.7.
  • Alpha To Selection: Creates a new selection mask based on the alpha value of any given pixel. This can be particular useful in combination with a layer creayed with the text tools.
  • Copy Selection: The selection is used as a mask to copy the selected area to the clipboard.
  • Cut Selection: The selected are is both coppied to the clip biard and erased in the active layer.
  • Erase Selection: The selected are is earsed in the active layer.
• Layers Menu:
  • Selection To Alpha: Creates or sets the alpha channel to match the current selected area

Selection Tools ARexx Commands

To pass ARexx commands to the selection tools you must use the SketchBlock ARexx command COMMANDTOOL The names of the tools for the purposes of COMMANDTOOL are "Rectangle Select" "Elipse Select" "Colour Select" and "Flood Select".

SET

ATTR/K,STEM/K,VALUESTRING

ATTR/K

Specify an individual attribute to set

VALUESTRING

Combined with the ATTR keyword this provides the value for one attribute.

STEM/K

Pass the name of a stem variable to set a number of attributes at the same time, see GET for list of attributes

GET

ATTR/K,STEM/K

Retrieves the current settings via a STEM varaible.

ATTR

Specify a single attribute to query. The value will be resturn in RESULT

STEM/K

Pass the variable to which the settings will be added. The values will be added to the stem variable useing the name above with no index component.

SELECTACTION

Set the selection action optionsd are REPLACE ADD SUBTRACT INTERSECT

COLORRANGE

For colour and flood tools sets the range of colurs matched, values 0 to 100

SOFTSELECT

Set or disable sof selection. 0 or 1

In addition a special ATTRS variable will be set which contains a list of avalaible attrs. The total stem var may look like so:

STEM.ATTRS.0  3
STEM.ATTRS.1.ATTR SELECTACTION
STEM.ATTRS.2.ATTR COLORRANGE
STEM.ATTRS.3.ATTR SOFTSELECT
STEM.SELECTACTION REPLACE | ADD | SUBTRACT | INTERSECT 
STEM.COLORRANGE 1 (0-100)
STEM.SOFTSELECT 0 | 1

The attrs substemvariable allows discovery of attributes dynamically by scripts including any that might be added after this documention was written. See Rexx/makepreset.rexx in the SketchBlock distribution drawer for an example.

SELECT

PRJID/K/N,LAYID/N/K,X/N/A,Y/N/A,[WIDTH/N/A,HEIGHT/N/A]

Perform a selection action.

PRJID/K/N

The project to act on, curent active project if not supplied

LAYID/N/K

The layer to operate on current active layer if not supplied

X/N/A

X coordinate of effective mouse click point

Y/N/A

Y coodinate

[WIDTH/N/A,HEIGHT/N/A

Width and height for elipse and rectangle tools

The latest version of this document can be found at www.broad.ology.org.uk/amiga/sketchblock/selectiontools.html