Adobe 65007312 - Photoshop Lightroom Programmer's Manual page 49

C 3: Creating Export and Publish Services
HAPTER
It then calls
you wish to start an export without using the export dialog, you can make the same calls yourself.)
In this discussion, an Export Service Provider is called a service, and an Export Filter Provider is called a filter.
Stage 1: Deciding how the photos should be rendered
If the service has defined an
argument, the export-settings table, and allows the service to force certain render settings to its preferred
or required settings. For example, to force a specific size for the exported photos, you could use this
definition:
updateExportSettings = function( exportSettings )
exportSettings.LR_size_maxHeight = 400
exportSettings.LR_size_maxWidth = 400
end
The filters, if any, are not involved at this stage.
Stage 2: Deciding what photos should be rendered
The filters are invoked from top-to-bottom. For each filter:
If it is defined, the
photo is removed from the list of photos to export (and thus does not get passed to the downstream
consumer). If it returns true, the photo remains in the list and is passed to the downstream consumer.
If
shouldRenderPhotos()
consumer.
Stage 3: Requesting renditions
1. The export session (
every photo that was not removed in Stage 2. (The actual rendering of the photos does not start yet.)
During this stage, Lightroom can show a dialog message if a photo already exists at the proposed
destination location. You can control this behavior using the
export settings table.
2. The service's
provided that performs the steps described below.
I
MPORTANT
runs in its own task (using
running simultaneously. Several photos can be in process simultaneously by different providers. This
allows the overall export operation to complete much more quickly than it would if every photo had to go
through all of the steps before the processing of the next photo could begin.
3. The
processRenderedPhotos()
each rendition to be completed by calling
completion of this loop in Stage 4.)
4. The service's rendition requests are sent to its upstream provider (that is, the bottom-most filter, or if
there are no filters, Lightroom's built-in render engine).
exportSession:doExportOnCurrentTask()
updateExportSettings()
shouldRenderPhotos()
is not defined for the filter, all photos are passed to the downstream
LrExportSession
processRenderedPhotos()
: Each of the providers (the export service, filters, and Lightroom's built-in rendering engine)
LrTasks
function, it is called. This function takes one
function is called for each photo. If it returns false, the
) generates rendition request objects (
function is called. If no such function exists, a default one is
), so these loops operate in parallel. It is likely that each provider will be
function calls
exportContext:renditions()
rendition:waitForRender()
Adding an export post-process action 49
, which performs the following operations. (If
LrExportRendition
LR_collisionHandling
. (We will discuss the
) for
setting in the
and then waits for