ACA 2015 - Highlighting and Selection Preview

Long-time users of Autodesk^® AutoCAD^® and Autodesk^® AutoCAD^® Architecture are likely familiar with the HIGHLIGHT system variable, which enables/disables highlighting of selected objects. Back before grips, enabling it was the only way to visually keep track of what objects were currently selected. The 2015 release adds a new effect to both selection highlighting and selection preview - the "glowing line" - along with the traditional dashed line (dashed and thickened for selection preview). Hardware acceleration has to be enabled in order for the glowing line effect to be displayed. The SELECTIONEFFECT System Variable allows you to choose between the two options (see below for details).

Selection Highlight with Glowing Lines

Selection Highlight with Dashed Lines

Selection preview allows you to see what object would be selected if you completed the current selection action. So, the object under the cursor that would be selected if you left clicked will get the selection preview as you move your cursor around the screen. If you start a selection rectangle or lasso (window or crossing) or a selection fence, the selection preview is applied to all objects that would be selected if you ended the selection method at that moment. The PRESELECTIONEFFECT System Variable (see below for details) allows you to choose between glowing lines and dashed/thickened lines. When glowing lines are enabled, you can distinguish already selected items from selection preview items by the color of the glow: a selected item will have a blue glow whereas an item that has selection preview applied have a gray glow.

Selection Preview with Glowing Lines

Selection Preview with Dashed and Thickened Lines

Depending upon your viewing preferences, machine capabilities and drawing size and complexity, you may find selection preview disruptive to your workflow. You do, however, have more control over this feature than just on or off. Selection preview can be globally turned on or off independently for two different conditions: when a command is active and when no command is active. This is controlled by the SELECTIONPREVIEW system variable (see below) or by using two of the toggles in the Options dialog, on the Selection tab, Preview area in the lower right corner, immediately under Selection preview. (The toggle settings reflect the current value of the SELECTIONPREVIEW system variable; checking or unchecking the toggles will modify the system variable accordingly.)

Control Selection Preview in the Options Dialog, Selection Tab

An additional level of control is provided by the PREVIEWFILTER system variable (see below for more details). This allows you to exclude certain types of objects from receiving the selection preview highlighting: objects on locked layers, external references, tables, groups, multiline text and hatches. In addition to assigning a value to the system variable directly, you can control this from the Options dialog, on the Selection tab, in the Preview area, by selecting the Visual Effect Settings button. This opens the Visual Effect Settings dialog; the Selection Preview Filter area on the right side contains toggles for excluding each of the previously listed object types (checked = no selection preview).

Exclude Object Types from Selection Preview in the Visual Effects Settings Dialog

Details on the system variables that affect highlighting and selection preview follow. The variable names are linked to the 2015 Online Help topic for that variable.

HIGHLIGHT (not saved; initial value 1)
0 - Turns off object selection highlighting
1 - Turns on object selection highlighting
(No effect on preselection highlighting, just selection highlighting.)

SELECTIONEFFECT (saved in registry)
0 - Dashed lines and no solid fill for faces.
1 - When hardware acceleration is on, displays glowing line highlighting effect and solid fill for faces.

SELECTIONPREVIEW (saved in registry; bitcoded sum of the following values)
0 - Off
1 - On when no commands are active
2 - On when a command prompts for object selection

PRESELECTIONEFFECT (saved in registry)
0 - Dashed and thickened lines, no solid fill for faces.
1 - When hardware acceleration is on, displays glowing line highlighting effect and solid fill for faces.

PREVIEWFILTER (saved in registry; bitcoded sum of the following values)
0 - Excludes nothing
1 - Excludes objects on locked layers
2 - Excludes objects in xrefs
4 - Excludes tables
8 - Excludes multiline text objects
16 - Excludes hatch objects
32 - Excludes objects in groups

HIGHLIGHTSMOOTHING (saved in registry)
0 - Turns off anti-aliasing effect on object selection highlighting.
1 - Turns on anti-aliasing effect on object selection highlighting.
(Hardware acceleration must be on. Affects both preselection and selection highlighting. On my computer at home, there was little to no effect on AEC objects, as seen in the image below; on my computer at work, the effect was more noticeable on AEC objects, and for all objects the stair-stepping effect had much shorter steps than the image below for lines without hightligh smoothing.)

Lines with HIGHLIGHTSMOOTHING Set to 0 [Left] and 1 [Right]

Walls with HIGHLIGHTSMOOTHING Set to 0 [Left] and 1 [Right]