feat(gui): load or create thumbnail videos on project loading

If the temp files still exist, they are assumed to be
correct and are loaded. Otherwise, the thumbnail videos
are recreated before entering the DiffScreen.

Signed-off-by: Anton Kriese <[email protected]>

Author: akriese

GUI/src/main/kotlin/logic/ThumbnailVideoCreator.kt

@@ -1,37 +1,46 @@
 package logic
 
+import androidx.compose.runtime.MutableState
+import models.AppState
 import org.bytedeco.javacv.FFmpegFrameRecorder
 import wrappers.IterableFrameGrabber
 import wrappers.Resettable2DFrameConverter
 import java.awt.image.BufferedImage
 import java.io.File
 
-fun createThumbnailVideo(
+/**
+ * Creates a scaled video from the input video as a temp file.
+ *
+ * @param inputPath [String] containing the path to the input video.
+ * @param scale [Float] containing the scaling factor, must be greater than 0f.
+ * @return [String] containing the path to the scaled video.
+ */
+fun createScaledVideo(
     inputPath: String,
-    downScaling: Float = 0.5f,
+    scale: Float = 0.5f,
 ): String {
-    assert(downScaling > 0.0f && downScaling <= 1.0f) { "Downscaling factor must be between 0 and 1" }
+    assert(scale > 0.0f) { "Scaling factor must be positive!" }
     val outputPath = kotlin.io.path.createTempFile(prefix = "gui_thumbnail_video", suffix = ".mkv").toString()
 
     val grabber = IterableFrameGrabber(File(inputPath))
 
     val inWidth = grabber.imageWidth
     val inHeight = grabber.imageHeight
 
-    val outWidth = (inWidth * downScaling).toInt()
-    val outHeight = (inHeight * downScaling).toInt()
+    val outWidth = (inWidth * scale).toInt()
+    val outHeight = (inHeight * scale).toInt()
 
     val recorder = FFmpegFrameRecorder(outputPath, outWidth, outHeight)
-
     val converter = Resettable2DFrameConverter()
 
+    // copy some metadata over
     recorder.frameRate = grabber.frameRate
     recorder.videoCodec = grabber.videoCodec
 
     recorder.start()
 
     for (image in grabber) {
-        // do something with the frame
+        // scale down the image and record it
         val scaledImage = BufferedImage(outWidth, outHeight, BufferedImage.TYPE_3BYTE_BGR)
         scaledImage.createGraphics().drawImage(image.getScaledInstance(outWidth, outHeight, 0), 0, 0, null)
         recorder.record(converter.convert(scaledImage))
@@ -42,3 +51,16 @@ fun createThumbnailVideo(
 
     return outputPath
 }
+
+/**
+ * Creates the thumbnail videos for the reference and current videos and updates their paths in the global state.
+ *
+ * @param state [MutableState]<[AppState]> containing the global state.
+ */
+fun createThumbnailVideos(state: MutableState<AppState>) {
+    // create the thumbnail videos
+    val tempReference = createScaledVideo(state.value.videoReferencePath!!, 0.25f)
+    val tempCurrent = createScaledVideo(state.value.videoCurrentPath!!, 0.25f)
+
+    state.value = state.value.copy(thumbnailVideoPathReference = tempReference, thumbnailVideoPathCurrent = tempCurrent)
+}

GUI/src/main/kotlin/ui/components/general/ProjectManager.kt

@@ -10,12 +10,14 @@ import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.DpOffset
 import androidx.compose.ui.unit.dp
 import com.fasterxml.jackson.module.kotlin.readValue
+import logic.createThumbnailVideos
 import logic.getVideoMetadata
 import models.AppState
 import models.JsonMapper
 import org.bytedeco.javacv.FFmpegFrameGrabber
 import org.bytedeco.javacv.FFmpegFrameRecorder
 import org.bytedeco.javacv.Frame
+import java.io.File
 
 /**
  * Dropdown menu to open and save projects
@@ -131,6 +133,15 @@ fun handleOpenProject(
         state.value.outputPath = path
         // reset unsaved changes
         state.value.hasUnsavedChanges = false
+
+        // if the temp thumbnail videos exist, use them. Otherwise, create them again which might take a few seconds
+        if (!(
+                state.value.thumbnailVideoPathReference?.let { File(it).exists() } == true &&
+                    state.value.thumbnailVideoPathCurrent?.let { File(it).exists() } == true
+            )
+        ) {
+            createThumbnailVideos(state)
+        }
     } else {
         errorText.value = "The selected file does not contain a valid project."
     }

GUI/src/main/kotlin/ui/components/selectVideoScreen/ComputeDifferencesButton.kt

@@ -13,7 +13,7 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.dp
 import kotlinx.coroutines.*
-import logic.createThumbnailVideo
+import logic.createThumbnailVideos
 import logic.differenceGeneratorWrapper.DifferenceGeneratorWrapper
 import logic.getVideoMetadata
 import models.AppState
@@ -117,14 +117,6 @@ suspend fun runComputation(
     state.value = state.value.copy(screen = Screen.DiffScreen, hasUnsavedChanges = true)
 }
 
-fun createThumbnailVideos(state: MutableState<AppState>) {
-    // create the thumbnail videos
-    val tempReference = createThumbnailVideo(state.value.videoReferencePath!!, 0.25f)
-    val tempCurrent = createThumbnailVideo(state.value.videoCurrentPath!!, 0.25f)
-
-    state.value = state.value.copy(thumbnailVideoPathReference = tempReference, thumbnailVideoPathCurrent = tempCurrent)
-}
-
 private fun calculateVideoDifferences(
     state: MutableState<AppState>,
     errorDialogText: MutableState<String?>,