fixes #70 - store a ref to preview frame & update preview synchronously

removing the Python thread might not have been necessary. I will test this next

2 files changed, 23 insertions, 24 deletions

diff --git a/src/gui/mainwindow.py b/src/gui/mainwindow.py
index f6de763..2bfc4e3 100644
--- a/src/gui/mainwindow.py
+++ b/src/gui/mainwindow.py
@@ -4,7 +4,7 @@
     This shows a preview of the video being created and allows for saving
     projects and exporting the video at a later time.
 '''
-from PyQt5 import QtCore, QtGui, QtWidgets, uic
+from PyQt5 import QtCore, QtWidgets, uic
 import PyQt5.QtWidgets as QtWidgets
 from PIL import Image
 from queue import Queue
@@ -754,7 +754,7 @@ class MainWindow(QtWidgets.QMainWindow):
             self.autosave()
         self.updateWindowTitle()
 
-    @QtCore.pyqtSlot(QtGui.QImage)
+    @QtCore.pyqtSlot('QImage')
     def showPreviewImage(self, image):
         self.previewWindow.changePixmap(image)
 
diff --git a/src/video_thread.py b/src/video_thread.py
index 0472aa3..0a95201 100644
--- a/src/video_thread.py
+++ b/src/video_thread.py
@@ -114,21 +114,19 @@ class Worker(QtCore.QObject):
         for audioI in range(0, self.audioArrayLen, self.sampleSize):
             self.compositeQueue.put(audioI)
 
-    def previewDispatch(self):
+    def showPreview(self, frame):
         '''
-            Grabs frames from the previewQueue, adds them to the checkerboard
-            and emits a final QImage to the MainWindow for the live preview
+            Receives a final frame that will be piped to FFmpeg,
+            adds it to the checkerboard and emits a final QImage
+            to the MainWindow for the live preview
         '''
         background = Checkerboard(self.width, self.height)
-
-        while not self.stopped:
-            audioI, frame = self.previewQueue.get()
-            if time.time() - self.lastPreview >= 0.06 or audioI == 0:
-                image = Image.alpha_composite(background.copy(), frame)
-                self.imageCreated.emit(QtGui.QImage(ImageQt(image)))
-                self.lastPreview = time.time()
-
-            self.previewQueue.task_done()
+        image = Image.alpha_composite(background.copy(), frame)
+        # We must store a reference to this QImage
+        # or else Qt will garbage-collect it on the C++ side
+        self.latestPreview = ImageQt(image)
+        self.imageCreated.emit(QtGui.QImage(self.latestPreview))
+        self.lastPreview = time.time()
 
     @pyqtSlot()
     def createVideo(self):
@@ -145,7 +143,6 @@ class Worker(QtCore.QObject):
         self.compositeQueue.maxsize = 20
         self.renderQueue = PriorityQueue()
         self.renderQueue.maxsize = 20
-        self.previewQueue = PriorityQueue()
 
         self.reset()
         progressBarValue = 0
@@ -307,15 +304,13 @@ class Worker(QtCore.QObject):
         self.dispatchThread.daemon = True
         self.dispatchThread.start()
 
-        self.lastPreview = 0.0
-        self.previewDispatch = Thread(
-            target=self.previewDispatch, name="Render Dispatch Thread"
-        )
-        self.previewDispatch.daemon = True
-        self.previewDispatch.start()
+        # Last time preview was drawn
+        self.lastPreview = time.time()
 
         # Begin piping into ffmpeg!
-        frameBuffer = {}
+        frameBuffer = {
+            # audioI: bytes ready to be piped
+        }
         progressBarValue = 0
         self.progressBarUpdate.emit(progressBarValue)
         self.progressBarSetText.emit("Exporting video...")
@@ -328,14 +323,17 @@ class Worker(QtCore.QObject):
                         break
                     # else fetch the next frame & add to the buffer
                     audioI_, frame = self.renderQueue.get()
-                    frameBuffer[audioI_] = frame
+                    frameBuffer[audioI_] = frame.copy()
                     self.renderQueue.task_done()
                 if self.canceled:
                     break
 
+                # Update live preview
+                if time.time() - self.lastPreview > 0.5:
+                    self.showPreview(frameBuffer[audioI])
+
                 try:
                     self.out_pipe.stdin.write(frameBuffer[audioI].tobytes())
-                    self.previewQueue.put([audioI, frameBuffer.pop(audioI)])
                 except Exception:
                     break
 
@@ -348,6 +346,7 @@ class Worker(QtCore.QObject):
                         "Exporting video: %s%%" % str(int(progressBarValue))
                     )
 
+
         numpy.seterr(all='print')
 
         self.closePipe()