feat(convert): add to PDF conversion

docs/source/features_table.md

@@ -6,21 +6,21 @@ The following summarizes the different presentation features Manim Slides offers
 :widths: auto
 :align: center
 
-| Feature / Constraint | [`present`](reference/cli.md) | [`convert --to=html`](reference/cli.md) | [`convert --to=pptx`](reference/cli.md) |
-| :--- | :---: | :---: | :---: |
-| Basic navigation through slides | Yes | Yes | Yes |
-| Replay slide | Yes | No | No |
-| Pause animation | Yes | No | No |
-| Play slide in reverse | Yes | No | No |
-| Slide count | Yes | Yes (optional) | Yes (optional) |
-| Animation count | Yes | No | No |
-| Needs Python with Manim Slides installed | Yes | No | No |
-| Requires internet access | No | Yes | No |
-| Auto. play slides | Yes | Yes | Yes |
-| Loops support | Yes | Yes | Yes |
-| Fully customizable | No | Yes (`--use-template` option) | No |
-| Other dependencies | None | A modern web browser | PowerPoint or LibreOffice Impress[^1]
-| Works cross-platforms | Yes | Yes | Partly[^1][^2] |
+| Feature / Constraint | [`present`](reference/cli.md) | [`convert --to=html`](reference/cli.md) | [`convert --to=pptx`](reference/cli.md) | [`convert --to=pdf`](reference/cli.md)
+| :--- | :---: | :---: | :---: | :---: |
+| Basic navigation through slides | Yes | Yes | Yes | Yes (static image) |
+| Replay slide | Yes | No | No | N/A |
+| Pause animation | Yes | No | No | N/A |
+| Play slide in reverse | Yes | No | No | N/A |
+| Slide count | Yes | Yes (optional) | Yes (optional) | N/A |
+| Animation count | Yes | No | No | N/A |
+| Needs Python with Manim Slides installed | Yes | No | No | No
+| Requires internet access | No | Yes | No | No |
+| Auto. play slides | Yes | Yes | Yes | N/A |
+| Loops support | Yes | Yes | Yes | N/A |
+| Fully customizable | No | Yes (`--use-template` option) | No | No |
+| Other dependencies | None | A modern web browser | PowerPoint or LibreOffice Impress[^1] | None |
+| Works cross-platforms | Yes | Yes | Partly[^1][^2] | Yes |
 :::
 
 [^1]: If you encounter a problem where slides do not automatically play or loops do not work, please [file an issue on GitHub](https://github.com/jeertmans/manim-slides/issues/new/choose).

docs/source/reference/sharing.md

@@ -150,14 +150,35 @@ reason.
 
 ### With PowerPoint (*EXPERIMENTAL*)
 
-A recent conversion feature is to the PowerPoint format, thanks to the `python-pptx` package. Even though it is fully working, it is still considered in an *EXPERIMENTAL* status because we do not exactly know what versions of PowerPoint (or LibreOffice Impress) are supported.
+A recent conversion feature is to the PowerPoint format, thanks to the
+`python-pptx` package. Even though it is fully working,
+it is still considered in an *EXPERIMENTAL* status because we do not
+exactly know what versions of PowerPoint (or LibreOffice Impress) are supported.
 
 Basically, you can create a PowerPoint in a single command:
 
 ```bash
 manim-slides convert --to=pptx BasicExample basic_example.pptx
 ```
 
-All the videos and necessary files will be contained inside the `.pptx` file, so you can safely share it with anyone. By default, the `poster_frame_image`, i.e., what is displayed by PowerPoint when the video is not playing, is the first frame of each slide. This allows for smooth transitions.
+All the videos and necessary files will be contained inside the `.pptx` file, so
+you can safely share it with anyone. By default, the `poster_frame_image`, i.e.,
+what is displayed by PowerPoint when the video is not playing, is the first
+frame of each slide. This allows for smooth transitions.
 
-In the future, we hope to provide more features to this format, so feel free to suggest new features too!
+In the future, we hope to provide more features to this format,
+so feel free to suggest new features too!
+
+### Static PDF presentation
+
+If you ever need backup slides, that are only made of PDF pages
+with static images, you can generate such a PDF with the following command:
+
+```bash
+manim-slides convert --to=pdf BasicExample basic_example.pdf
+```
+
+Note that you will lose all the benefits from animated slides. Therefore,
+this is only recommended to be used as a backup plan. By default, the last frame
+of each slide will be printed. This can be changed to be the first one with
+`-cframe_index=first`.

manim_slides/convert.py

@@ -14,7 +14,8 @@
 import pptx
 from click import Context, Parameter
 from lxml import etree
-from pydantic import BaseModel, FilePath, PositiveInt, ValidationError
+from PIL import Image
+from pydantic import BaseModel, FilePath, PositiveFloat, PositiveInt, ValidationError
 from tqdm import tqdm
 
 from . import data
@@ -75,6 +76,7 @@ def from_string(cls, s: str) -> Type["Converter"]:
         """Returns the appropriate converter from a string name."""
         return {
             "html": RevealJS,
+            "pdf": PDF,
             "pptx": PowerPoint,
         }[s]
 
@@ -367,6 +369,62 @@ def convert_to(self, dest: Path) -> None:
             f.write(content)
 
 
+class FrameIndex(str, Enum):
+    first = "first"
+    last = "last"
+
+
+class PDF(Converter):
+    frame_index: FrameIndex = FrameIndex.last
+    resolution: PositiveFloat = 100.0
+
+    class Config:
+        use_enum_values = True
+        extra = "forbid"
+
+    def open(self, file: Path) -> None:
+        return open_with_default(file)
+
+    def convert_to(self, dest: Path) -> None:
+        """Converts this configuration into a PDF presentation, saved to DEST."""
+
+        def read_image_from_video_file(file: Path, frame_index: FrameIndex) -> Image:
+            cap = cv2.VideoCapture(str(file))
+
+            if frame_index == FrameIndex.last:
+                index = cap.get(cv2.CAP_PROP_FRAME_COUNT)
+                cap.set(cv2.CAP_PROP_POS_FRAMES, index - 1)
+
+            ret, frame = cap.read()
+
+            if ret:
+                frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
+                return Image.fromarray(frame)
+            else:
+                raise ValueError("Failed to read {image_index} image from video file")
+
+        images = []
+
+        for i, presentation_config in enumerate(self.presentation_configs):
+            presentation_config.concat_animations()
+            for slide_config in tqdm(
+                presentation_config.slides,
+                desc=f"Generating video slides for config {i + 1}",
+                leave=False,
+            ):
+                file = presentation_config.files[slide_config.start_animation]
+
+                images.append(read_image_from_video_file(file, self.frame_index))
+
+        images[0].save(
+            dest,
+            "PDF",
+            resolution=self.resolution,
+            save_all=True,
+            append_images=images[1:],
+        )
+
+
 class PowerPoint(Converter):
     left: PositiveInt = 0
     top: PositiveInt = 0
@@ -513,7 +571,7 @@ def callback(ctx: Context, param: Parameter, value: bool) -> None:
 @click.argument("dest", type=click.Path(dir_okay=False, path_type=Path))
 @click.option(
     "--to",
-    type=click.Choice(["html", "pptx"], case_sensitive=False),
+    type=click.Choice(["html", "pdf", "pptx"], case_sensitive=False),
     default="html",
     show_default=True,
     help="Set the conversion format to use.",