Enable fast saving mode for PNGs

[myaaaaaaaaa]

Makes saving PNGs 2.5x faster for me at only 2% (!) increase in filesize, although please note that I only did basic testing. Presumably, more compressible images would end up with a bigger filesize penalty.

Helps with Movie Maker, see godotengine/godot-proposals#4751

Fixes #51868

[fire]

I'm interested. Not able to review this week due to a brief break from godot engine 4.0 release.

[Calinou]

Benchmark

CPU: Intel Core i9-13900K
GPU: GeForce RTX 4090
OS: Fedora 37

Time taken to render https://github.com/Calinou/godot-movie-maker-demo:

Type	AVI	PNG - master	PNG - this PR
Editor 1280×720	1m07s	6m25s	1m41s (3.81× faster than master)
Editor 3840×2160	6m49s	48m00s	10m44s (4.47× faster than master)
Release template 1280×720	39s	6m36s	1m48s (3.67× faster than master)
Release template 3840×2160	3m31s	47m06s	9m37s (4.9× faster than master)

File size of first frame in 3840×2160:

PNG - master	PNG - this PR
7,173 KB	9,432 KB

Considering saving time is the most important criterion in Movie Maker, I'd say this increase in file size is fine. It's common for games in general to take large, unoptimized screenshots to ensure they save quickly (so they don't interrupt the action for too long).

Script used for testing

#!/bin/bash
set -euo pipefail
IFS=$'\n\t'

DEMO_DIR="$HOME/Documents/Godot/godot-movie-maker-demo"
mkdir -p "$DEMO_DIR/out"
export MANGOHUD=0

echo "#################################"
echo "Editor 1280x720"
echo "#################################"
echo "AVI:"
time bin/godot.linuxbsd.editor.x86_64.master --path "$DEMO_DIR" --write-movie "out/out.avi"
echo "End AVI."
echo "Master:"
time bin/godot.linuxbsd.editor.x86_64.master --path "$DEMO_DIR" --write-movie "out/out.png"
echo "End master."
echo "This PR:"
time bin/godot.linuxbsd.editor.x86_64 --path "$DEMO_DIR" --write-movie "out/out.png"
echo "End this PR."

echo "#################################"
echo "Release export template 1280x720"
echo "#################################"
echo "AVI:"
time bin/godot.linuxbsd.template_release.x86_64.master --path "$DEMO_DIR" --write-movie "out/out.avi"
echo "End AVI."
echo "Master:"
time bin/godot.linuxbsd.template_release.x86_64.master --path "$DEMO_DIR" --write-movie "out/out.png"
echo "End master."
echo "This PR:"
time bin/godot.linuxbsd.template_release.x86_64 --path "$DEMO_DIR" --write-movie "out/out.png"
echo "End this PR."

echo "#################################"
echo "Editor 3840x2160"
echo "#################################"
echo "AVI:"
time bin/godot.linuxbsd.editor.x86_64.master --path "$DEMO_DIR" --write-movie "out/out.avi" --fullscreen
echo "End AVI."
echo "Master:"
time bin/godot.linuxbsd.editor.x86_64.master --path "$DEMO_DIR" --write-movie "out/out.png" --fullscreen
echo "End master."
echo "This PR:"
time bin/godot.linuxbsd.editor.x86_64 --path "$DEMO_DIR" --write-movie "out/out.png" --fullscreen
echo "End this PR."

echo "#################################"
echo "Release export template 3840x2160"
echo "#################################"
echo "AVI:"
time bin/godot.linuxbsd.template_release.x86_64.master --path "$DEMO_DIR" --write-movie "out/out.avi" --fullscreen
echo "End AVI."
echo "Master:"
time bin/godot.linuxbsd.template_release.x86_64.master --path "$DEMO_DIR" --write-movie "out/out.png" --fullscreen
echo "End master."
echo "This PR:"
time bin/godot.linuxbsd.template_release.x86_64 --path "$DEMO_DIR" --write-movie "out/out.png" --fullscreen
echo "End this PR."

[fire]

! Amazing. Will need to wait for a production team review.

[clayjohn]

Won't this increase the filesize of every PNG saved by the engine? Not just the ones created by the MovieMaker feature?

[fire]

It's common for games in general to take large, unoptimized screenshots to ensure they save quickly (so they don't interrupt the action for too long).

I think @myaaaaaaaaa is saying that's a good tradeoff.

[Calinou]

Won't this increase the filesize of every PNG saved by the engine? Not just the ones created by the MovieMaker feature?

It will, but the engine defaults to saving lossless WebP when importing images since 3.5. As a result, this PR doesn't affect the size of the .godot/ folder and exported PCK by default.

That said, we could make save_png() accept a compression mode parameter (uncompressed, fast compression, best compression).¹

Footnotes

1. Uncompressed PNG may still be slower to save than saving a dedicated uncompressed format such as TGA or BMP, due to general format inefficiencies. That said, we don't have TGA or BMP encoders in Godot yet, while enabling libpng's uncompressed mode is a 1-line change. ↩

[PeterMarques]

In the "Marshalls.raw_to_base64(vp.get_texture().get_data().save_png_to_buffer())" that is very slow, and have several bottleneck points, one being that get_texture() itself, that can be better implemented to have bigger delay but lower cpu usage, the Save_png_to_buffer(), is still the one that consumes the most CPU time.

#76465
#75877

[akien-mga]

That said, we could make save_png() accept a compression mode parameter (uncompressed, fast compression, best compression).

I agree we should make this a flag in save_png(). Also discussed it with @reduz who agreed.

Could default to fast compression, but users should still have a way to opt in to best compression if they value size over compression speed.

Needs more work after discussion.