# V2 Colorblind Simulation Shader

This runbook covers `TODOS.phase-72.72.13.1.1`: an engine-level colorblind
simulation shader for protanopia, deuteranopia, tritanopia, and achromatopsia
filters as a post-process.

## Runtime Contract

The V2UI runtime owns the colorblind simulation post-process surface:

- shader source: `V2/ue/Shaders/V2/Accessibility/V2ColorblindSimulation.usf`
- shader mapping: `/V2/Accessibility`
- shader virtual path: `/V2/Accessibility/V2ColorblindSimulation.usf`
- C++ header: `V2/ue/Source/V2UI/Public/V2ColorblindSimulation.h`
- C++ source: `V2/ue/Source/V2UI/Private/V2ColorblindSimulation.cpp`
- automation spec:
  `V2/ue/Source/V2Tests/Private/UI/ColorblindSimulationShader.spec.cpp`
- contract:
  `V2/ue/Content/V2/UI/Accessibility/ColorblindSimulationShader_V2_Contract.json`
- focused checker: `V2/ue/Tools/check-v2-colorblind-simulation-shader.py`

The module maps the shader directory during `FV2UIModule::StartupModule` with
`AddShaderSourceDirectoryMapping`, so the pass can resolve the project shader by
virtual path.

## Supported Modes

The post-process mode list is:

- `Protanopia`
- `Deuteranopia`
- `Tritanopia`
- `Achromatopsia`

The shader keeps `Off` as the no-op runtime state and publishes the four
deficiency filters as selectable simulation modes.

## Post-Process Behavior

`FV2ColorblindPostProcessPass` defines the engine-facing pass descriptor:

- pass name: `V2.ColorblindSimulation.PostProcess`
- entry point: `MainPS`
- consumes scene color
- writes scene color
- applies after tonemap
- supports runtime strength blending from `0.0` to `1.0`

The pixel shader samples `SceneColorTexture`, applies the selected simulation
matrix, clamps the result, and blends it with the original scene color by
`V2ColorblindSimulationStrength`.

## Matrix Validation

The C++ helper exposes the same normalized matrix coefficients as the shader:

- protanopia: `0.567, 0.433, 0.000 / 0.558, 0.442, 0.000 / 0.000, 0.242, 0.758`
- deuteranopia:
  `0.625, 0.375, 0.000 / 0.700, 0.300, 0.000 / 0.000, 0.300, 0.700`
- tritanopia: `0.950, 0.050, 0.000 / 0.000, 0.433, 0.567 / 0.000, 0.475, 0.525`
- achromatopsia: `0.299, 0.587, 0.114` repeated across all three output rows

`FV2ColorblindSimulationSettings::IsValidSettings` requires a normalized
strength, full-frame scene-color simulation, and post-process execution.

## Verification

```bash
python3 V2/ue/Tools/check-v2-colorblind-simulation-shader.py
python3 V2/ue/Tools/check-v2-ci-workflow.py
python3 V2/tools/validate-v2-docs.py
python3 -m py_compile V2/ue/Tools/check-v2-colorblind-simulation-shader.py V2/ue/Tools/check-v2-ci-workflow.py
python3 -m json.tool V2/ue/Content/V2/UI/Accessibility/ColorblindSimulationShader_V2_Contract.json
python3 -m json.tool V2/ue/Build/Horde/v2-buildgraph-job.json
```

The automation spec is registered as
`V2.UI.Accessibility.ColorblindSimulationShader.AssetContract`.

Required gates:

- `colorblind-simulation-shader-source`
- `colorblind-simulation-shader-modes`
- `colorblind-simulation-shader-post-process`
- `colorblind-simulation-shader-matrices`
- `colorblind-simulation-shader-automation`
- `colorblind-simulation-shader-ci-wired`