Project Eagle Core - Advanced Weather System

Introduction

In vanilla GTA: San Andreas, weather uses time-based interpolation, it blends between two weather types over the course of an in-game hour using InterpolationValue. However, when you cross from Los Santos to San Fierro, the game instantly switches to that region's weather list with no spatial blending. The colors still interpolate over time, but you get whichever region you're standing in, immediately.

Project Eagle Core keeps vanilla's time-based interpolation but adds a revolutionary second dimension: spatial interpolation. We also expanded the timecyc format from SA's limited parameters to support GTA III, Vice City, Liberty City Stories, Vice City Stories, and Bully's lighting systems, plus authentic PostFX color filters that replicate each game's exact visual style.

Key Improvements

• 23 → 111 weather types across multiple cities (LC, VC, BW, and more)
• Dual interpolation: Time (vanilla) + Space (new)
• Extended timecyc format: 73 parameters supporting GTA III/VC/LCS/VCS/Bully data
• Authentic PostFX filters: recreation of each game's color grading
• Snow weather with dynamic particles
• Hurricanes with malfunctioning traffic lights
• Volumetric clouds with 37 3D sprites

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Dual Interpolation System Explained

Two-Dimensional Weather Blending

Project Eagle Core blends weather in two independent dimensions simultaneously:

1. Time Interpolation (Vanilla SA Behavior - Preserved)

• InterpolationValue ranges from 0.0 → 1.0 during each in-game hour
• Blends OldWeatherType → NewWeatherType
• Formula: InterpolationValue = CClock::ms_nGameClockMinutes / 60.0f

2. Spatial Interpolation (NEW)

A 400-unit weather transition zone around region borders:

  Distance from boundary:
    -200 units → RegionBlendFactor = 0.0  (old region)
      0 units → RegionBlendFactor = 0.5  (boundary)
    +200 units → RegionBlendFactor = 1.0  (new region)
    

How They Work Together

1. Time blend determines which hour values to use
2. Spatial blend determines contribution from each region
3. Final weather = combined dual-blended output

  LS_TimeBlended = 0.25 * LS_Hour15 + 0.75 * LS_Hour16
  SF_TimeBlended = 0.25 * SF_Hour15 + 0.75 * SF_Hour16
  FinalColor = 0.25 * LS_TimeBlended + 0.75 * SF_TimeBlended
    

Extended TimeCyc Format

Vanilla SA uses 43 parameters per entry. Project Eagle expands this to 73 parameters including:

• Blur colors
• Directional light color
• Material multiplier
• Fog color
• Top cloud color
• Dark factor
• Radiosity intensity
• Wind multiplier
• Handling type
• Color filter
• Weather variant
• Flags

Multi-Game Support

Each weather type can adopt lighting from:

SA • III • VC • LCS • VCS • BLY • PS2

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Authentic PostFX Color Filters

Filter	Description
SA	San Andreas default
III	GTA III style
VC	Vice City warmth
VCS	Vice City Stories
LCS	Liberty City Stories
BLY	Bully
PS2	PS2 SA

New Weather Features

❄️ Snow System

• Individual snowflakes rendered as sprites
• 0.2 × 0.2 unit textured quads
• 80 × 80 × 30 unit spawn box
• Wind-affected drift
• Indoor detection

🌀 Hurricanes

• Heavy rain
• Strong wind multiplier
• Traffic lights alternate yellow/off every 500ms

☁️ Clouds

• 37 cloud sprites
• Dual-texture sprites
• Sun highlighting
• Fog fading

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By The Numbers

Feature	Vanilla SA	Project Eagle Core
Weather types	23	111
Regions	4	17+
Timecyc parameters	43	73
Interpolation dimensions	1	2
PostFX filters	1	7
Region transitions	Instant	400-unit blend
Snow	None	800 particles
Clouds	2D	37 volumetric sprites
Hurricane effects	None	Traffic light malfunction

Project Eagle Core's weather overhaul transforms GTA SA into a living, breathing world, featuring dual interpolation, expanded lighting, authentic PostFX pipelines, 111 weather types, real snow, hurricanes, volumetric clouds, and seamless region transitions.

- Madhav2609