Fix error when calling requestJpegThumbnail()

In LrC 14 (WIN) requestJpegThumbnail() fails on every first call for an image.

Author: capricorn8

focuspoints.lrdevplugin/MogrifyUtils.lua

@@ -31,7 +31,7 @@ local mogrifyPath
 
 --[[
 -- Call mogrify with 'params'
--- Raises a LrError in case of an execution error 
+-- Raises a LrError in case of an execution error
 --]]
 local function mogrifyExecute(params, script)
   if mogrifyPath == nil then
@@ -44,15 +44,15 @@ local function mogrifyExecute(params, script)
   local cmdline = '\"' .. mogrifyPath .. '\" '
   if script then
     scriptName = createMagickScript(params)
-    cmdline = cmdline .. '-script ' .. '\"' .. scriptName .. '\"' 
+    cmdline = cmdline .. '-script ' .. '\"' .. scriptName .. '\"'
   else
     cmdline = cmdline .. 'mogrify ' .. params
   end
-  logDebug('mogrifyExecute', cmdline ) 
+  logDebug('mogrifyExecute', cmdline )
   local stat = LrTasks.execute( '\"' .. cmdline .. '\"' )
   if stat ~= 0 then
-    logError('mogrifyDraw', 'Error calling: ' .. cmdline ) 
-    LrErrors.throwUserError("Error calling 'mogirfy.exe' Please check plugin configuration")
+    logError('mogrifyDraw', 'Error calling: ' .. cmdline )
+    LrErrors.throwUserError("Error calling 'mogrify.exe' Please check plugin configuration")
   end
   if script then
     local prefs = LrPrefs.prefsForPlugin( nil )
@@ -61,39 +61,57 @@ local function mogrifyExecute(params, script)
       LrFileUtils.delete(scriptName)
     end
   end
- 
-end
 
+end
 
 
 --[[
 -- Export the catalog photo to disk
 -- photo: Lr catalog photo
 -- xSize: width in pixel of the create temporary photo
 -- ySize: height in pixel of the create temporary photo
--- 
+--
 -- requestJpegThumbnail treats the size as minimum value, thus the image on the disk maybe larger
+--
+-- Note: in LrC 14 (at least on WIN) this function fails on the first call for an image.
+-- Analysis and proposal for a fix by John R. Ellis (LR SDK luminary on Adobe forums):
+--
+-- requestJpegThumbnail() appears to call the callback synchronously if the requested thumbnail
+-- is in an internal cache. Otherwise, it returns immediately and calls the callback asynchronously
+-- after the thumbnail is generated and loaded into the cache, which could take anywhere from
+-- 0.01 seconds to a couple seconds if the photo has to be re-rendered.
+-- In order to make sure the thumbnail has been written to file before proceeding with the next
+-- steps, exportToDisk() should busy wait until the callback is invoked.
+-- photo:getRawMetadata() has to be executed outside the callback, because this method "yields"
+-- which is not allowed in a no-yielding context (asynchronous call of callback)
 --]]
 local function exportToDisk(photo, xSize, ySize)
+  local done = false
+  local orgPath = photo:getRawMetadata("path")
   local thumb = photo:requestJpegThumbnail(xSize, ySize, function(data, errorMsg)
     if data == nil then
       logError('exportToDisk', 'No thumbnail data')
       LrErrors.throwUserError("Export to disk failed. No thumbnail data received.")
     else
-      local orgPath = photo:getRawMetadata("path")
       local leafName = LrPathUtils.leafName( orgPath )
       local leafWOExt = LrPathUtils.removeExtension( leafName )
       local tempPath = LrPathUtils.getStandardFilePath( "temp" )
       fileName = LrPathUtils.child( tempPath, leafWOExt .. "-fpoints.jpg" )
-      logDebug('exportToDisk', "filename = " .. fileName ) 
+      logDebug('exportToDisk', "filename = " .. fileName )
 
       local localFile = io.open(fileName, "w+b")
       localFile:write(data)
       localFile:close()
     end
+    done = true
   end)
+  if not done then
+  -- busy wait for (asynchronous) callback to complete
+    while not done do LrTasks.sleep (0.1) end
+  end
 end
 
+
 --[[
 -- Resize the disk image to the given ize
 -- xSize: width in pixel
@@ -118,26 +136,26 @@ local function mapIconToStrokewidthAndColor(name)
 end
 
 --[[
--- Build the mogirfy draw parameters base on the focuspointsTable
+-- Build the mogrify draw parameters base on the focuspointsTable
 --]]
 local function buildDrawParams(focuspointsTable)
-  local para = nil
-  local sw = nil
-  local color = nil
-  
+  local para
+  local sw
+  local color
+
   local params = '-fill none '
   for i, fpPoint in ipairs(focuspointsTable) do
     if fpPoint.template.center ~= nil then
-      local x = math.floor(tonumber(fpPoint.points.center.x)) 
+      local x = math.floor(tonumber(fpPoint.points.center.x))
       local y = math.floor(tonumber(fpPoint.points.center.y))
       para = '-stroke red -fill red -draw \"circle ' ..x .. ',' .. y .. ' ' .. x+3 .. ',' .. y  .. '\" -fill none '
-      logDebug('buildCmdLine', '[' .. i .. '] ' .. para ) 
+      logDebug('buildCmdLine', '[' .. i .. '] ' .. para )
       params = params .. para
     end
     if fpPoint.template.corner ~= nil then
       sw, color = mapIconToStrokewidthAndColor(fpPoint.template.corner.fileTemplate)
       para = '-strokewidth ' .. sw .. ' -stroke ' .. color .. ' '
-      local tlx = math.floor(tonumber(fpPoint.points.tl.x)) 
+      local tlx = math.floor(tonumber(fpPoint.points.tl.x))
       local tly = math.floor(tonumber(fpPoint.points.tl.y))
       local brx = math.floor(tonumber(fpPoint.points.br.x))
       local bry = math.floor(tonumber(fpPoint.points.br.y))
@@ -146,48 +164,48 @@ local function buildDrawParams(focuspointsTable)
         local x = tlx
         tlx = brx
         brx = x
-      end 
-      if fpPoint.rotation == 0 or fpPoint.rotation == 360 then 
+      end
+      if fpPoint.rotation == 0 or fpPoint.rotation == 360 then
         para = para .. '-draw \"roundRectangle ' .. tlx .. ',' .. tly .. ' ' .. brx .. ',' .. bry .. ' 1,1\" '
       else
         local trx = math.floor(tonumber(fpPoint.points.tr.x))
         local try = math.floor(tonumber(fpPoint.points.tr.y))
         local blx = math.floor(tonumber(fpPoint.points.bl.x))
         local bly = math.floor(tonumber(fpPoint.points.bl.y))
-        para = para .. '-draw \"polyline ' .. trx .. ',' .. try .. ' ' .. tlx .. ',' .. tly .. ' '  
+        para = para .. '-draw \"polyline ' .. trx .. ',' .. try .. ' ' .. tlx .. ',' .. tly .. ' '
                   .. blx .. ',' .. bly .. ' ' .. brx .. ',' .. bry .. ' ' .. trx .. ',' .. try .. '\" '
       end
-      logDebug('buildCmdLine', '[' .. i .. '] ' .. para .. ' ' .. fpPoint.template.corner.fileTemplate) 
+      logDebug('buildCmdLine', '[' .. i .. '] ' .. para .. ' ' .. fpPoint.template.corner.fileTemplate)
       params = params .. para
     end
   end
   return params
 end
 
 --[[
--- Create a temprory disk impage for the given Lightroom catalog photo. 
+-- Create a temprory disk impage for the given Lightroom catalog photo.
 -- photo: Lr catalog photo
 -- xSize: width in pixel of the create temporary photo
 -- ySize: height in pixel of the create temporary photo
 --]]
 function MogrifyUtils.createDiskImage(photo, xSize, ySize)
-  logInfo('MogrifyUtils.createDiskImage', photo:getFormattedMetadata( 'fileName' ) .. ' ' .. xSize .. ' ' .. ySize ) 
+  logInfo('MogrifyUtils.createDiskImage', photo:getFormattedMetadata( 'fileName' ) .. ' ' .. xSize .. ' ' .. ySize )
   exportToDisk(photo, xSize, ySize)
   mogrifyResize(xSize, ySize)
   return fileName
 end
 
 
---[[ 
+--[[
 -- Draw the focus poins bases on focuspointsTable (see 'DefaultPointRenderer.prepareRendering' for adescription of the table)
 --]]
 function MogrifyUtils.drawFocusPoints(focuspointsTable)
-  local params = buildDrawParams(focuspointsTable)  
+  local params = buildDrawParams(focuspointsTable)
   mogrifyExecute(params, true)
 end
 
 
---[[ 
+--[[
 -- Creates a temporay script file for Magick. Returns the name of the temp file
 --]]
 function createMagickScript(params)
@@ -201,8 +219,8 @@ function createMagickScript(params)
 end
 
 
---[[ 
--- Deletes the temporary file (created by 'MogrifyUtils.exportToDisk') 
+--[[
+-- Deletes the temporary file (created by 'MogrifyUtils.exportToDisk')
 -- Raises a LrError in case that the deletion fails
 --]]
 function MogrifyUtils.cleanup()