// XC_BUILTIN_SKYBOX_VULKAN_PS
#version 450

layout(set = 0, binding = 0, std140) uniform EnvironmentConstants {
    vec4 gSkyboxTopColor;
    vec4 gSkyboxHorizonColor;
    vec4 gSkyboxBottomColor;
    vec4 gCameraRightAndTanHalfFov;
    vec4 gCameraUpAndAspect;
    vec4 gCameraForwardAndUnused;
};

layout(location = 0) in vec2 vNdc;

layout(location = 0) out vec4 fragColor;

void main() {
    float tanHalfFov = gCameraRightAndTanHalfFov.w;
    float aspect = gCameraUpAndAspect.w;

    vec3 viewRay = normalize(
        gCameraForwardAndUnused.xyz +
        vNdc.x * aspect * tanHalfFov * gCameraRightAndTanHalfFov.xyz +
        vNdc.y * tanHalfFov * gCameraUpAndAspect.xyz);

    float vertical = clamp(viewRay.y, -1.0, 1.0);
    vec3 color = gSkyboxHorizonColor.rgb;
    if (vertical >= 0.0) {
        color = mix(gSkyboxHorizonColor.rgb, gSkyboxTopColor.rgb, pow(clamp(vertical, 0.0, 1.0), 0.65));
    } else {
        color = mix(gSkyboxHorizonColor.rgb, gSkyboxBottomColor.rgb, pow(clamp(-vertical, 0.0, 1.0), 0.55));
    }

    fragColor = vec4(color, 1.0);
}