Mixwell_UVtoPosition.osl

// SPDX-License-Identifier: MIT
// Copyright (c) 2026 Doug L. James and Ethan James

///////////////////////////////////////////////////////////////////////
////  Mixwell UV-to-Position Shader for Redshift OSL                 //
////  Maps UV coordinates to 2D Mixwell position (pMixwell)          //
////  @author Doug L James, 2026                                     //
///////////////////////////////////////////////////////////////////////

shader Mixwell_UVtoPosition(
    // UV Scale and Offset
    float uvScale = 2.0
        [[ string label = "UV Scale",
           string help = "Scale factor from UV [0,1] to physical coordinates",
           float min = 0.1,
           float max = 20.0 ]],
    float uvOffsetX = 0.0
        [[ string label = "UV Offset X",
           string help = "Horizontal offset applied before scaling",
           float min = -10.0,
           float max = 10.0 ]],
    float uvOffsetY = 0.0
        [[ string label = "UV Offset Y",
           string help = "Vertical offset applied before scaling",
           float min = -10.0,
           float max = 10.0 ]],
    
    // Optional rotation
    float rotation = 0.0
        [[ string label = "Rotation (deg)",
           string help = "Rotation angle applied after scaling",
           float min = 0.0,
           float max = 360.0 ]],
    
    // Optional aspect ratio correction
    float aspectRatio = 1.0
        [[ string label = "Aspect Ratio",
           string help = "X/Y aspect ratio correction (1.0 = square)",
           float min = 0.1,
           float max = 10.0 ]],
    
    // Outputs
    output vector pMixwell = 0
        [[ string label = "pMixwell",
           string help = "2D Mixwell position coordinate" ]],
    output float pMixwell_x = 0
        [[ string label = "pMixwell.x" ]],
    output float pMixwell_y = 0
        [[ string label = "pMixwell.y" ]]
)
{
    // Apply offset, then scale
    float px = (u + uvOffsetX) * uvScale * aspectRatio;
    float py = (v + uvOffsetY) * uvScale;
    
    // Apply rotation if specified
    if (rotation != 0.0) {
        float ang = radians(rotation);
        float c = cos(ang);
        float s = sin(ang);
        float rx = c * px - s * py;
        float ry = s * px + c * py;
        px = rx;
        py = ry;
    }
    
    pMixwell = vector(px, py, 0.0);
    pMixwell_x = px;
    pMixwell_y = py;
}