-Pcb-rnd aides the user in creating real pcb product, composed of real -physical layers. pcb-rnd also refers to layers to conceptualize this -process, but pcb-rnd layers are different than the physical layers. +The main use of pcb-rnd is to aide the user in the process of producing real +pcbs composed of real physical layers. pcb-rnd also refers to layers to +conceptualize this process, but pcb-rnd layers are different than the +physical layers.
-Unlike a physical layer, a pcb-rnd layer has no thickness. It is a 2 -dimensional, logical canvas, similar to layers in image manipulation software -like gimp. In pcb-rnd there are explicit and virtual layers. An explicit -layer contains drawing primitives (objects) placed by the user. The user has -full control over an explicit layer: objects can be added or removed or changed -any time. A virtual layer has no such flexibility: pcb-rnd computes its content -from explicit layers and there's no way to change the result directly. A layer -is always part of a layer group. +Unlike a physical layer, a pcb-rnd layer has no thickness. Any pcb-rnd +layer is always part of a layer group. It is a 2 dimensional logical +canvas, similar to layers in image manipulation software like GIMP. In pcb-rnd +there are explicit, virtual or implicit layers. An +explicit layer contains drawing primitives (objects) +placed by the user. The user has full control over an explicit layer: objects +can be added or removed or changed any time. A virtual or implicit layer has no +such flexibility: pcb-rnd computes its content from explicit layers and there's +no way for the user to change the result directly. +
+Pcb-rnd currently maintains some layers types as virtual layers for +compatability with the PCB package. In a pcb-rnd board design started from +default configuration options, the mask, silk, and paste layers currently start +out as virtual layers. The content for these layers is computed by pcb-rnd as +for a virtual or explicit layer, until the user decides to use features that +require user control over one or more of the layers in the group. At that +point, the virtual layer is replaced with an explicit layer group. +
+For example, in pcb-rnd when using one of the gtk GUIs, if the user right +clicks on a solder mask ('mask') layer and choose an option to 'insert new +layer before this one', pcb-rnd replaces the virtual mask layer with an explicit +mask layer group. The mask layer group can contain one to many pcb-rnd layers +each with individual settings to control implicit generation, and additive or +subtractive behavior when adding objects to the layers.
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Pcb-rnd supports a small number of basic drawing objects, from which complex objects can be build. The following figure demonstrates all basic objects: