Fix rendering bugs that make some scenes look wrong

[beingsuz]

Requested by beingsuz · project thread

Before: twinkling particles (stars, fireflies) faded to nothing within about two seconds. On a 16:10 or 4:3 screen the default fit showed more than the scene and smeared its top and bottom rows; on a square screen it stretched the picture. Children of rotated layers were placed on the wrong side. Particle systems ignored their parent layers, scripts and timelines. A layer whose last effect failed to build could draw as an opaque box.

After: those scenes draw the way Wallpaper Engine draws them, as far as the code can be checked without real wallpapers (see Verification).

This is the first batch from an audit of the renderer; more fixes follow on this branch once example wallpapers arrive.

Changes

Particles

• oscillatealpha / oscillatesize multiplied the current value every frame and nothing reset it: alpha went from 1 to 0.0002 in 120 frames. Colour, alpha and size are now rebuilt from the spawn values each frame, and every operator scales what the earlier ones left (so alphafade + alphachange both apply instead of the last one winning).
• colorchange honours starttime / endtime.
• Particle systems are placed through world_xf, so they follow parents, puppet attachments, script moves and timelines (retransform_dirty now covers them).
• A particle system hidden at load is still built, so a script can show it later.

Layout

• --scaling default covers the screen like fill, cropping the overhang, instead of overscanning narrower screens and stretching square ones.
• world_xf rotated a child's offset by +angle, while every quad rotates by -angle. Children of rotated parents were mirrored around them.
• auto_projection doubled the extent: origins are measured from the corner, not the centre.
• The cursor is mapped through the scaling window (crop, focus, zoom), so cursor effects react under the real cursor. Parallax y was inverted relative to x.

Effects

• When the planned last pass is dropped, the pass that reaches the scene is rebuilt with the layer's blend instead of its effect's normal (One/Zero).
• g_Daytime is the time of day instead of 0.
• uniform int members (detected from naga's member type) are written as i32, not as float bits.

Verification

• cargo fmt --check, cargo clippy --workspace --all-targets -D warnings and cargo test --workspace pass on Linux with lavapipe.
• New tests: oscillate no longer compounds and two alpha operators multiply (both fail on main), default fit never reaches past the content, child rotation matches the parent quad, auto projection size, cursor through the crop window, particle world transform, int uniform bytes.
• Not tested: any real Wallpaper Engine scene, and Windows. The container has no WE assets. The parallax direction and the auto projection meaning are inferred from kirie's own conventions, not checked against Wallpaper Engine.

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📥 Commits

Reviewing files that changed from the base of the PR and between 0a55364 and b77dc34.

📒 Files selected for processing (9)

• crates/kirie-render/src/particle/operator.rs
• crates/kirie-render/src/particle/system.rs
• crates/kirie-render/src/scaling.rs
• crates/kirie-render/src/scene/extras.rs
• crates/kirie-render/src/scene/model.rs
• crates/kirie-render/src/scene/pipeline.rs
• crates/kirie-render/src/scene/renderer.rs
• crates/kirie-render/src/scene/uniforms.rs
• crates/kirie-render/tests/particle.rs

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