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downscale preview image for faster save #917

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Merged
Try merged 6 commits into from
Apr 20, 2026
Merged

downscale preview image for faster save #917

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78f3d81
downscale preview image for faster save
jairus-kope Apr 12, 2026
8e4dfb4
preserve aspect ratio and original texture format
jairus-kope Apr 13, 2026
143b96f
Merge branch 'master' into pr/917
Try Apr 18, 2026
e20905b
gpu based downscale
Try Apr 18, 2026
37edeb6
use jpg for save-game priviews
Try Apr 18, 2026
57ba6fb
cleanup
Try Apr 18, 2026
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32 changes: 31 additions & 1 deletion game/mainwindow.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,34 @@

using namespace Tempest;

namespace {
Pixmap downscaleSavePreviewPixmap(Pixmap src) {
if(src.isEmpty() || src.format()!=TextureFormat::RGBA8)
return src;
constexpr uint32_t kThumbW = 640, kThumbH = 480;
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@Try Try Apr 12, 2026

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480 is overkill in term of how small image. 1440p, maybe?
Note: images can be extracted as screen-shoots.

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@jairus-kope jairus-kope Apr 13, 2026 •
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This change does not affect screen-shoots (F11 key I believe) which will keep as is.
This is only for the thumbnails in the load/save screen. images there are a small part of the screen so I wouldn't think they need a high resolution. anyways I've changed it to 1024 (maybe take this from ini settings?)
Regarding timings (I tested this manually with my phone's stopwatch so not that accurate..):
without this change it produced a 6K HDR (6016x3384), though my screen resolution is 3008x1692 - save took ~7 seconds
1440p took ~1.5 seconds
640x480 took ~0.3 seconds (keeping aspect ration of 16:9 will probably take less)
1024x768 took ~0.5 seconds
1024x576 ie. keeping 16:9 aspect ratio (using the latest code changes i pushed) - took about i guess ~0.4 seconds
Note that these changes also totally remove the lag of the load/save screen loading.

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@Try Try Apr 13, 2026

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This is only for the thumbnails in the load/save screen

Yes; what I've been pointing to is fact that screen-shoot can be extracted from the save as *.png.
For move precise time you can leverage Application::tickCount utility.

const uint32_t w = src.w(), h = src.h();

if(w<=kThumbW || h<=kThumbH)
return src;

Pixmap out(kThumbW, kThumbH, TextureFormat::RGBA8);
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@Try Try Apr 12, 2026

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This code doesn't preserve proportions. 640x480 is 4:3 ratio, but most screens today is 16:9.

TextureFormat::RGBA8

While today it's rgba8, but there is HDR support in works - so, you should not relay strongly on format. Probably downsampling image on GPU would make more sense, to take care of formats and performance.

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@jairus-kope jairus-kope Apr 13, 2026

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Good points. I modified the code to preserve aspect ratio and also the original texture format. Though I don't have the means to test it on HDR.
yeah I agree. downsampling on GPU would probably be best. Feel free to use this as a temp fix or just PoC

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@Try Try Apr 13, 2026

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Will it be OK, to you if I'll implement the feature on my own, with gpu-support and you your data only as reference?
Asking, since merging first and do full rewrite a week after is also not ideal.

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@jairus-kope jairus-kope Apr 13, 2026

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Sure. please go ahead. just happy to have assisted with finding and debugging this issue. I think solving it will definitely improve the gaming experience.

const auto* s = static_cast<const uint32_t*>(src.data());
auto* d = static_cast<uint32_t*>(out.data());

// Copy source pixel map to reduced pixel map using Nearest-Neighbor interpolation
for(uint32_t y=0; y<kThumbH; ++y) {
const uint32_t sy = std::min(h-1u, uint32_t((size_t(y)*h)/kThumbH));
const uint32_t rowOffset = sy * w;

for(uint32_t x=0; x<kThumbW; ++x) {
const uint32_t sx = std::min(w-1u, uint32_t((size_t(x)*w)/kThumbW));
d[y * kThumbW + x] = s[rowOffset + sx];
}
}
return out;
}
}

MainWindow::MainWindow(Device& device)
: Window(Maximized),device(device),swapchain(device,hwnd()),
atlas(device),renderer(swapchain),
Expand Down Expand Up @@ -1062,7 +1090,9 @@ void MainWindow::loadGame(std::string_view slot) {

void MainWindow::saveGame(std::string_view slot, std::string_view name) {
auto tex = renderer.screenshoot(cmdId);
auto pm = device.readPixels(textureCast<const Texture2d&>(tex));

// reduce size of the save entry preview screenshot for faster save & load
auto pm = downscaleSavePreviewPixmap(device.readPixels(textureCast<const Texture2d&>(tex)));

if(dialogs.isActive())
return;
Expand Down