Visibility control by freezing or thawing layers behaves straightforward: no entities that are located on frozen layers will display.
If the layer on which a block was inserted becomes frozen, then ALL content of that block will no longer ze visible, regardless of the layer on which entities were located at creation time of the block.
If a block is inserted on a thawed layer, but contains content placed on a layer that becomes frozen, then only such content will no longer be visible.
The On/Off setting behaves different from the Thawed/Frozen setting, specifically concerning the behavior for block content placed on layer 0.
Entities that were on layer 0 at creation time of a block, will obey the On/Off setting of the layer on which the block is inserted, so these elements will behave as is they were placed on the layer on which the block is inserted. Entities that were not on layer 0 at creation time of a block, will obey the layer on/off setting in a normal way.
A block is made with entities from layers 0, 1 and 2. The block is inserted on layer 1.
Now, this is what happens:
- when we switch off layer 0:
the block content that at block creation time was on layer 0, will remain visible because
it now acts as if it were on layer 1!
- when we switch off layer 1:
the block content that at block creation was on layer 0, becomes invisible,
as well as the block content that initially was on layer 1.
- when we switch off layer 2:
only the block content that at creation time was on layer 2 becomes invisible.
The way the color of entities is controlled is related to this behavior:
Entities that at block creation time were on layer 0 and had color property 'BYLAYER' will obey the color property of the layer on which the block is inserted.
The appearance of an entity is controlled by its COLOR, LINETYPE, LINEWEIGHT and TRANSPARENCY setting. In addition to a specific value, the BYLAYER and BYBLOCK options are available. These options cause an entity to adopt the property either fromthe layer or the block into which it is inserted.
To draw all entities in the default property set for the current layer.
When you insert the block in a drawing, all entities inherit the currently selected defaults for new entities.
If you insert a block that contains entities originally drawn on layer 0 and assigned color and linetype BYLAYER, it is placed on the current layer and assumes the color and linetype of that layer. If you insert a block that contains entities originally drawn on other layers or with explicitly specified colors or linetypes, the block retains the original settings.
If you insert a block that contains entities originally assigned color and linetype BYBLOCK, and the block itself has the color and linetype BYLAYER, those entities adopt the color and linetype of the layer onto which they are inserted. If the block is assigned an explicit color or linetype, such as red or dashed, those entities adopt those qualities.
If a block contains a mixture of colors, inserting blocks when the color is set to BYBLOCK can produce unpredictable results.