on the most fine-grained level, vkdt's processing is organised as a directed graph of nodes that directly correspond to kernels executed on the device. a module you usually see in the ui may consist of several such nodes.
for some use cases, however, this is still not coarse grained enough. for
instance if you want to draw brush strokes on an image for dodging or burning,
you'll need a draw module, a blend module, and as a minimum an exposure
module to alter the pixels under the mask at all. to adjust the mask to the
edges of the input images, it is useful to include a guided filter module
too. now this is already four additional modules and quite laborious to add
manually.
for such cases, there are blocks, templates of sub-graphs to be added as a
whole. the example above is realised in the draw.cfg block. to apply it,
press ctrl-b (default hotkey) in darkroom mode and select the draw.cfg
block. it will query you where to insert the block, since blocks are templates:
they will be inserted between two modules which are already on your graph.
additionally, you can specify the common instance name of the modules that will
be newly added (maybe dodge is a good instance name in our example).
blocks are located in the data/blocks/ subdirectory of the installation, and
custom user-specific blocks will also be read from ~/.config/vkdt/blocks/.
as an example, start from the data/blocks/draw.cfg block. it is a standard
vkdt .cfg file but contains a few variables that will be replaced before
the commands are appended to the history of the image:
INSTANCE the common instance name of new modulesOUTMOD the module name of the module which comes before the blockOUTINST the instance name of this moduleOUTCONN the connector name of the sameINMOD the module name of the module which comes after the blockININST the instance name of this moduleINCONN the connector name of the same.