UE5 Screen Space Particle Dissolve

The first step is calculating a 2D bounding box in screen space from the 3D bounding box of the target mesh. I get the mesh's 8 bounding box corners in world space, project each corner to clip space using the View.WorldToClip matrix, then find min/max X and Y to get the screen rectangle.

This gives me the area on screen where the character appears, which I use for both the dissolve origin and particle spawning region.

// For each of the 8 bounding box corners:
float3 target = Center + HalfExtent * dir[i];
float4 clip = mul(float4(target, 1), View.WorldToClip);
minX = min(minX, clip.x);
maxX = max(maxX, clip.x);
// ... same for Y

The dissolve is driven by animating a threshold value. Each pixel compares its distance from a center point against this threshold using a step function - as the threshold increases, more pixels pass the test and get clipped.

The dummy mesh (with stencil value) dissolves with a slight delay from the main mesh. This timing offset is what creates the visible stencil region at the dissolving edge - the area where the main mesh has already disappeared but the dummy mesh hasn't yet.

I add noise to the threshold comparison to break up the edge. Without noise you get a clean geometric cutoff; with noise it looks more organic. The noise tiling is adjustable so I can control how chunky or smooth the edge breakup looks.

Edge emissive adds a glow at the dissolve boundary - same technique as most dissolve effects, just masking based on proximity to the threshold value.

The Niagara emitter runs on GPU sim (required to read GBuffer). Particles spawn within the screen-space bounding box, then I convert each particle's clip space position back to world coordinates using View.ClipToWorld. This places particles in 3D space but aligned to the screen rectangle.

The key trick is the two-mesh stencil setup: I overlap two copies of the target mesh. The dummy mesh has a Custom Depth Stencil Value set (I used 2). The dummy dissolves with a slight delay from the main mesh, so the stencil buffer shows only the dissolving edge region.

In Niagara, I read the GBuffer's stencil value at each particle's screen position. If it matches the dummy mesh's stencil value, the particle stays alive. Otherwise it gets killed. This filters particles to only appear at the dissolving edge.

// Particle filtering in Niagara:
// 1. Convert world position to screen UV
// 2. Sample stencil value from GBuffer
// 3. If stencil == targetValue → alive
// 4. Otherwise → kill particle

I experimented with spawning directly from mesh triangles, but the particle placement ends up uneven depending on vertex density. The screen-space bounds method gives more consistent distribution.

The models are from Unreal Engine free assets - I don't own them and didn't make them. Most of these assets have VFX input functions built into their materials, which is great for pipeline work. I can plug my effect in without touching the original material.

When I do need to make changes, I duplicate the material and edit the copy. Never touch the source.