Add Screen-Space Global Illumination (SSGI) with configurable quality tiers

[Noa3]

Adds a screen-space path tracing approximation for indirect diffuse lighting. Rays are marched in screen space from each fragment along cosine-weighted hemisphere directions to gather light bounces from nearby visible surfaces.
New option: RT_SUNLIGHT_TRACING

Quality tiers: OFF / Low (2 rays, 6 steps) / Medium (3 rays, 8 steps) / High (4 rays, 12 steps)
RT_GI_STRENGTH: Intensity slider (25–200%)
RT_GI_RADIUS: Ray march distance (1.0–8.0 blocks)

Core implementation (lib/lighting/screenSpaceGI.glsl)

Cosine-weighted hemisphere sampling with golden-ratio-based quasi-random sequences
Depth-aware intersection with thickness threshold to reject back-face hits
Uses texelFetch and precomputed invSteps/farMinusNear to minimize per-fragment work

Integration

Injected in deferred1.glsl after SSAO, before PBR reflections — reuses linearZ0 when SSAO/outlines already computed it
shaders.properties: new RT_LIGHTING_SETTINGS submenu under Lighting, profile defaults (OFF through High, Low for VeryHigh, Medium for Ultra), slider registration
en_US.lang: display names and descriptions for all three settings

Minor cleanup

shadowSampling.glsl: sqrt(x*x + y*y) → length(xy)

[Copilot]

Pull request overview

This PR adds Screen-Space Global Illumination (SSGI) to approximate indirect diffuse lighting through screen-space ray marching. The implementation traces multiple rays per fragment along cosine-weighted hemisphere directions to gather light bounces from nearby visible surfaces.

Changes:

• Adds SSGI with three quality tiers (Low: 2 rays/6 steps, Medium: 3 rays/8 steps, High: 4 rays/12 steps) plus configurable strength and radius sliders
• Integrates SSGI into deferred1.glsl after SSAO and before PBR reflections, with optimizations to reuse linearZ0 when available
• Updates shader properties, language files, and profile defaults (OFF for most profiles, Low for VeryHigh, Medium for Ultra)

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
shaders/shaders.properties	Adds RT_SUNLIGHT_TRACING to all quality profiles, creates RT_LIGHTING_SETTINGS submenu, registers new sliders
shaders/lib/common.glsl	Defines RT_SUNLIGHT_TRACING, RT_GI_STRENGTH, RT_GI_RADIUS options and enables SSGI_ENABLED when tracing is active
shaders/program/deferred1.glsl	Integrates SSGI call after SSAO, transforms world normals to view space, applies GI with configurable strength
shaders/lib/lighting/screenSpaceGI.glsl	Implements cosine-weighted hemisphere sampling and depth-aware ray marching with thickness threshold intersection testing
shaders/lib/lighting/shadowSampling.glsl	Refactors distance calculation to use length() for improved readability
shaders/lang/en_US.lang	Adds localized strings for RT_LIGHTING_SETTINGS menu and all three SSGI options

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[Copilot]

The define name RT_SUNLIGHT_TRACING is misleading and inconsistent with the feature it controls. This setting controls Screen-Space Global Illumination (SSGI) quality, not sunlight tracing. The name should be changed to something like RT_SSGI_QUALITY or SSGI_QUALITY to accurately reflect its purpose. This inconsistency also appears in shaders.properties (line 50) and could confuse future developers.

Suggested change

	#define RT_SUNLIGHT_TRACING 0 //[0 1 2 3]
	#define RT_SSGI_QUALITY 0 //[0 1 2 3]
	// Backwards compatibility alias for legacy configs/shaders
	#define RT_SUNLIGHT_TRACING RT_SSGI_QUALITY

[Copilot]

Incorrect coordinate space transformation. The sampleDir returned from CosWeightedHemisphereDir is already in view space (it's constructed in the tangent space of normalM, which is a view-space normal). Applying mat3(gbufferModelView) here incorrectly transforms it a second time. This line should simply be vec3 viewDir = sampleDir; or the transformation should be removed. This bug will cause rays to be traced in incorrect directions, significantly affecting the visual quality and correctness of the SSGI effect.

Suggested change

	vec3 viewDir = mat3(gbufferModelView) * sampleDir;
	vec3 viewDir = sampleDir;

[Noa3]

@copilot open a new pull request to apply changes based on the comments in this thread

[EminGT]

Now this looks really interesting. Thank you very much for your contribution :) I will check this out in more detail when I get some other higher priority things finished