Initial commit: add all skills files

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

shader-dev/reference/camera-effects.md

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+# Camera Effects Detailed Reference
+
+## Prerequisites
+- Ray marching fundamentals (ray origin, ray direction)
+- Multipass buffers (for accumulation-based DoF)
+- Hash functions for stochastic sampling
+
+## Thin Lens Model Derivation
+
+A real camera lens focuses light from a focal plane onto the sensor. Points not on the focal plane project to a **circle of confusion (CoC)** on the sensor.
+
+### Circle of Confusion Formula
+```
+CoC = |S2 - S1| × A × f / (S1 × (S2 - f))
+```
+Where:
+- `S1` = focal distance (distance to in-focus plane)
+- `S2` = object distance
+- `A` = aperture diameter
+- `f` = focal length
+
+### Simplified for Shaders
+```
+CoC ≈ apertureSize × |depth - focalDistance| / depth
+```
+
+### Ray-Based Implementation
+Instead of computing CoC per pixel, we model the physical process:
+1. Choose a random point on the aperture disk → new ray origin
+2. The focal point (where the original ray hits the focal plane) stays fixed
+3. New ray direction = `normalize(focalPoint - newOrigin)`
+4. Average many such samples → natural bokeh with correct occlusion
+
+### Aperture Shape
+- Circular: `vec2 p = sqrt(r) * vec2(cos(a), sin(a))` — uniform disk
+- Polygonal: reject samples outside polygon for hexagonal/octagonal bokeh
+- The `sqrt(r)` is critical for uniform distribution (area-preserving)
+
+## Poisson Disk Sampling
+
+Pre-computed 16-point Poisson disk for blur kernels:
+```glsl
+const vec2 poissonDisk[16] = vec2[](
+    vec2(-0.94201624, -0.39906216), vec2(0.94558609, -0.76890725),
+    vec2(-0.09418410, -0.92938870), vec2(0.34495938,  0.29387760),
+    vec2(-0.91588581,  0.45771432), vec2(-0.81544232, -0.87912464),
+    vec2(-0.38277543,  0.27676845), vec2(0.97484398,  0.75648379),
+    vec2(0.44323325, -0.97511554),  vec2(0.53742981, -0.47373420),
+    vec2(-0.26496911, -0.41893023), vec2(0.79197514,  0.19090188),
+    vec2(-0.24188840,  0.99706507), vec2(-0.81409955,  0.91437590),
+    vec2(0.19984126,  0.78641367),  vec2(0.14383161, -0.14100790)
+);
+```
+
+Advantages over regular grid: no structured aliasing patterns, better coverage per sample count.
+
+## Motion Blur Approaches
+
+### Stochastic Time Sampling (Ray Marching)
+For each pixel, pick a random time within the shutter interval:
+```
+t_sample = iTime + (rand - 0.5) * shutterDuration
+```
+Use `t_sample` for all scene animation. Accumulate multiple frames for convergence.
+
+### Velocity Buffer (Post-Process)
+1. Render scene + store per-pixel velocity vectors
+2. For each pixel, sample along the velocity direction
+3. Weight samples by distance from center (triangle filter)
+
+### Hybrid
+Use temporal accumulation (TAA-style) with per-frame time jitter — converges over frames with no per-frame cost increase.
+
+## Film Grain Characteristics
+
+Real film grain properties:
+- **Luminance-dependent**: More visible in shadows, less in highlights
+- **Temporally varying**: Different pattern each frame (use `fract(iTime)` in hash seed)
+- **Spatially uncorrelated**: Use pixel coordinates in hash, not UV (grain should be screen-resolution)
+- **Intensity**: 0.02-0.05 for subtle, 0.1+ for stylized/vintage look