Sun Glow Particles Retired

Project: Hadean chronicles.

Particle-based glow system retired. Shader-based flares and sunspots now in production, fully verified visually.

First Obstacle: The Edge-On Mesh

The Sun’s CPU particle system rendered as a tiny red speck instead of a soft corona. After ruling out data issues, configuration problems, and surface artifacts, the real culprit revealed itself via a diagnostic force-opaque test. The glow quad mesh was facing edge-on to the camera, rendering to near-zero width under the fixed top-down perspective. Once this geometry issue was diagnosed, other mechanical problems became clear.

The death-alpha on the color ramp had been commented out—particles just popped rather than fading. Outward radial acceleration was an entire hemisphere pointed inward, creating a frozen shell instead of a breathing corona.

The Pivot: Swap Particles for Shaders

CPU particles bring hidden costs: per-element simulation, alpha sorting, lifetime checks, and overdraw stacking. For a feature meant to complement a shader-driven surface, the limitations outweighed the benefits.

The final decision: add flares and sunspots directly into the fragment shader. Eliminates draw calls, removes CPU simulation, and lifts the performance and visual ceiling.

Shader Suite: Intrinsic Sun Effects

The new sun sphere shader introduces two independent organic effects:

• Flare Overlay — bright patches sampled from value noise and masked in via additive blending with soft fwidth() edges. Controls handle frequency, threshold, and intensity.
• Sunspot Darkening — dark patches applied as shadows on the surface. To avoid visual clashes with flares, a separate noise sample uses different scale and a fixed phase offset, applied as a multiplicative dimmer after all additive light contributions.

Both effects share a 2-hash, 3-octave value-noise utility—cheap, localized, and flickering in real time.

Visual Duels: Tuning by Screenshot

Several subtle regressions emerged with each adjustment, each caught and corrected through visual verification:

• After decoupling flare frequency from texture tiling, the result looked fractured along hash-lattice edges. Switched to separate spherical UV sampling to fix aliasing.
• With wavelength-limited scale, large regions of the disc interpolated into giant blocky polygons. Increased scale and added a third finer noise octave for smoother, smaller patches.
• Early mixing caused sunspots to be invisible, hidden by additive core and rim passes that ignored the darkening mask. Moved the pass after all additive contributions.
• Sunspot coverage was too heavy, producing oversized, blurry blotches. Tightened threshold and raised scale for sparse, smaller, crisper spots.

Outcome

The particle system code remains in place but dormant, with the glow emission call commented out. A planned hybrid (shader + dedicated arc sprites) was discussed but not adopted. The shader implementation now delivers a living, breathing corona without expensive particle infrastructure.