#version 430 core
// Sky mesh fragment shader — sample the object's diffuse texture with
// the scrolled UVs from the vertex stage. Unlit: sky meshes ARE the
// gradient (r12 §2.2), not a surface lit by the sun.
//
// The per-keyframe replace override can dim the mesh (Transparent) or
// brighten it (Luminosity); those two floats arrive as uTransparency /
// uLuminosity uniforms.

in vec2 vTex;
out vec4 fragColor;

uniform sampler2D uDiffuse;
uniform float uTransparency;    // 0 = fully visible, 1 = invisible
uniform float uLuminosity;      // 1 = normal, >1 makes the mesh glow
uniform vec4  uTint;            // per-object color tint (default white)

// Shared SceneLighting UBO — we only need the fog parameters to let the
// horizon band of the sky blend smoothly into the scene's fog color at
// the far edge, and the lightning flash to give storms their signature
// strobe.
struct Light {
    vec4 posAndKind;
    vec4 dirAndRange;
    vec4 colorAndIntensity;
    vec4 coneAngleEtc;
};
layout(std140, binding = 1) uniform SceneLighting {
    Light uLights[8];
    vec4  uCellAmbient;
    vec4  uFogParams;
    vec4  uFogColor;
    vec4  uCameraAndTime;
};

void main() {
    vec4 sampled = texture(uDiffuse, vTex);

    // Apply tint + luminosity. Retail's SkyObjReplace.Luminosity can push
    // above 1 to make the sun mesh brighter than its texture; r12 §2.3.
    vec3 rgb = sampled.rgb * uTint.rgb * uLuminosity;

    // Lightning additive bump — makes the sky itself flash during storms.
    rgb += uFogParams.z * vec3(0.5, 0.5, 0.55);

    rgb = min(rgb, vec3(1.2));  // soft clamp to let luminosity over-bright mildly

    float a = sampled.a * (1.0 - uTransparency) * uTint.a;
    if (a < 0.01) discard;
    fragColor = vec4(rgb, a);
}