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Fix many_foxes + motion blur = crash on WebGL (#18715)

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## Objective

Fix  #18714.

## Solution

Make sure `SkinUniforms::prev_buffer` is resized at the same time as
`current_buffer`.

There will be a one frame visual glitch when the buffers are resized,
since `prev_buffer` is incorrectly initialised with the current joint
transforms.

Note that #18074 includes the same fix. I'm assuming this smaller PR
will land first.

## Testing

See repro instructions in #18714. Tested on `animated_mesh`,
`many_foxes`, `custom_skinned_mesh`, Win10/Nvidia with Vulkan,
WebGL/Chrome, WebGPU/Chrome.
This commit is contained in:
Greeble 2025-04-06 18:51:22 +01:00 committed by GitHub
parent d82c359a5a
commit 2f80d081bc
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1 changed files with 20 additions and 2 deletions
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22
crates/bevy_pbr/src/render/skin.rs
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@ -211,7 +211,7 @@ pub fn prepare_skins(
// Swap current and previous buffers. // Swap current and previous buffers.
mem::swap(&mut uniform.current_buffer, &mut uniform.prev_buffer); mem::swap(&mut uniform.current_buffer, &mut uniform.prev_buffer);
// Resize the buffer if necessary. Include extra space equal to `MAX_JOINTS` // Resize the buffers if necessary. Include extra space equal to `MAX_JOINTS`
// because we need to be able to bind a full uniform buffer's worth of data // because we need to be able to bind a full uniform buffer's worth of data
// if skins use uniform buffers on this platform. // if skins use uniform buffers on this platform.
let needed_size = (uniform.current_staging_buffer.len() as u64 + MAX_JOINTS as u64) let needed_size = (uniform.current_staging_buffer.len() as u64 + MAX_JOINTS as u64)
@ -223,7 +223,7 @@ pub fn prepare_skins(
new_size += new_size / 2; new_size += new_size / 2;
} }
// Create a new buffer. // Create the new buffers.
let buffer_usages = if skins_use_uniform_buffers(&render_device) { let buffer_usages = if skins_use_uniform_buffers(&render_device) {
BufferUsages::UNIFORM BufferUsages::UNIFORM
} else { } else {
@ -235,6 +235,24 @@ pub fn prepare_skins(
size: new_size, size: new_size,
mapped_at_creation: false, mapped_at_creation: false,
}); });
uniform.prev_buffer = render_device.create_buffer(&BufferDescriptor {
label: Some("skin uniform buffer"),
usage: buffer_usages,
size: new_size,
mapped_at_creation: false,
});
// We've created a new `prev_buffer` but we don't have the previous joint
// data needed to fill it out correctly. Use the current joint data
// instead.
//
// TODO: This is a bug - will cause motion blur to ignore joint movement
// for one frame.
render_queue.write_buffer(
&uniform.prev_buffer,
0,
bytemuck::must_cast_slice(&uniform.current_staging_buffer[..]),
);
} }
// Write the data from `uniform.current_staging_buffer` into // Write the data from `uniform.current_staging_buffer` into