#version 430 core

// Per-vertex attributes
layout(location = 0) in vec3 aPosition;
layout(location = 1) in vec3 aNormal;
layout(location = 2) in vec2 aTexCoord;

// Per-instance model matrix, split across four vec4 attribute slots.
// A mat4 consumes 4 consecutive attribute locations, so locations 3-6 are
// all occupied by this single logical matrix.  The C# side must call
// VertexAttribPointer four times (one per row) and VertexAttribDivisor(loc, 1)
// on each of the four slots.
layout(location = 3) in vec4 aInstanceRow0;
layout(location = 4) in vec4 aInstanceRow1;
layout(location = 5) in vec4 aInstanceRow2;
layout(location = 6) in vec4 aInstanceRow3;

uniform mat4 uViewProjection;
uniform vec3 uLightDirection;   // world-space light direction (points FROM sun, matching ACME)
uniform float uAmbientIntensity;

out vec2 vTex;
out vec3 vWorldNormal;
out float vLightingFactor;

void main() {
    // Reconstruct the per-instance model matrix from its four row vectors.
    mat4 model = mat4(aInstanceRow0, aInstanceRow1, aInstanceRow2, aInstanceRow3);

    vec4 worldPos = model * vec4(aPosition, 1.0);
    gl_Position = uViewProjection * worldPos;

    // Transform normal into world space.
    vWorldNormal = normalize(mat3(model) * aNormal);
    vTex = aTexCoord;

    // Lambert + ambient matching ACME StaticObject.vert:
    //   LightingFactor = max(dot(Normal, -uLightDirection), 0.0) + uAmbientIntensity;
    vLightingFactor = max(dot(vWorldNormal, -uLightDirection), 0.0) + uAmbientIntensity;
}