#define_import_path bevy_pbr::mesh_functions

#import bevy_pbr::{
    mesh_view_bindings::view,
    mesh_bindings::mesh,
    mesh_types::MESH_FLAGS_SIGN_DETERMINANT_MODEL_3X3_BIT,
    view_transformations::position_world_to_clip,
}
#import bevy_render::maths::{affine3_to_square, mat2x4_f32_to_mat3x3_unpack}


fn get_model_matrix(instance_index: u32) -> mat4x4<f32> {
    return affine3_to_square(mesh[instance_index].model);
}

fn get_previous_model_matrix(instance_index: u32) -> mat4x4<f32> {
    return affine3_to_square(mesh[instance_index].previous_model);
}

fn mesh_position_local_to_world(model: mat4x4<f32>, vertex_position: vec4<f32>) -> vec4<f32> {
    return model * vertex_position;
}

// NOTE: The intermediate world_position assignment is important
// for precision purposes when using the 'equals' depth comparison
// function.
fn mesh_position_local_to_clip(model: mat4x4<f32>, vertex_position: vec4<f32>) -> vec4<f32> {
    let world_position = mesh_position_local_to_world(model, vertex_position);
    return position_world_to_clip(world_position.xyz);
}

fn mesh_normal_local_to_world(vertex_normal: vec3<f32>, instance_index: u32) -> vec3<f32> {
    // NOTE: The mikktspace method of normal mapping requires that the world normal is
    // re-normalized in the vertex shader to match the way mikktspace bakes vertex tangents
    // and normal maps so that the exact inverse process is applied when shading. Blender, Unity,
    // Unreal Engine, Godot, and more all use the mikktspace method.
    // We only skip normalization for invalid normals so that they don't become NaN.
    // Do not change this code unless you really know what you are doing.
    // http://www.mikktspace.com/
    if any(vertex_normal != vec3<f32>(0.0)) {
        return normalize(
            mat2x4_f32_to_mat3x3_unpack(
                mesh[instance_index].inverse_transpose_model_a,
                mesh[instance_index].inverse_transpose_model_b,
            ) * vertex_normal
        );
    } else {
        return vertex_normal;
    }
}

// Calculates the sign of the determinant of the 3x3 model matrix based on a
// mesh flag
fn sign_determinant_model_3x3m(instance_index: u32) -> f32 {
    // bool(u32) is false if 0u else true
    // f32(bool) is 1.0 if true else 0.0
    // * 2.0 - 1.0 remaps 0.0 or 1.0 to -1.0 or 1.0 respectively
    return f32(bool(mesh[instance_index].flags & MESH_FLAGS_SIGN_DETERMINANT_MODEL_3X3_BIT)) * 2.0 - 1.0;
}

fn mesh_tangent_local_to_world(model: mat4x4<f32>, vertex_tangent: vec4<f32>, instance_index: u32) -> vec4<f32> {
    // NOTE: The mikktspace method of normal mapping requires that the world tangent is
    // re-normalized in the vertex shader to match the way mikktspace bakes vertex tangents
    // and normal maps so that the exact inverse process is applied when shading. Blender, Unity,
    // Unreal Engine, Godot, and more all use the mikktspace method.
    // We only skip normalization for invalid tangents so that they don't become NaN.
    // Do not change this code unless you really know what you are doing.
    // http://www.mikktspace.com/
    if any(vertex_tangent != vec4<f32>(0.0)) {
        return vec4<f32>(
            normalize(
                mat3x3<f32>(
                    model[0].xyz,
                    model[1].xyz,
                    model[2].xyz
                ) * vertex_tangent.xyz
            ),
            // NOTE: Multiplying by the sign of the determinant of the 3x3 model matrix accounts for
            // situations such as negative scaling.
            vertex_tangent.w * sign_determinant_model_3x3m(instance_index)
        );
    } else {
        return vertex_tangent;
    }
}