Flags without "Flag Params" mod (based on a script by Ronyx69)

flag-params.cs

// Warning: Do not save vehicles after running this script without a game restart!

// The vertex paint of the mesh controls the amount of movement:
// white means no movement and black means maximum movement.
//
// If you're using multiple "flag" textures in one prop, (like vanilla flags)
// the flag must be entirely black and everything else should be white,
// and you can't use the strength variable, otherwise the UV mapping will break.
// The flag should be UV mapped onto the flag on the bottom right of the texture.
//
// If you're using just one texture, 
// you can use shades of gray to control which parts move more or less,
// and also use the strength variable to reduce the movement.
//
// LOD also moves, so it should be treated the same way as the main model.

// Flag grid on the texture: leave at defaults if you're not using multiple flag textures in one prop
var columns = 1; // amount of vertical columns
var rows = 1; // amount of horizontal rows
Vector2 topLeft = new Vector2(0, 0); // top left corner x,y position (measured from top left) in pixels
Vector2 bottomRight = new Vector2(0, 0); // bottom right corner x,y position (measured from top left) in pixels

// Flag movement:
// movement strength (0.0 - 1.0)
// can't be used if you're using multiple flag textures in one prop
var strength = 1.0f; 


Vector3 axis = new Vector4(0.0f, 1.0f, 0.0f); // movement axis
Vector3 pivot = new Vector4(0.0f, 0.0f, 0.0f); // pivot point of the flag, where it is "attached"

var asset = ToolsModifierControl.toolController.m_editPrefabInfo as PropInfo;
var shader = Shader.Find("Custom/Props/Prop/Flag");
asset.m_material.shader = shader; if (asset.m_lodMaterial) asset.m_lodMaterial.shader = shader;
var tex = asset.m_material.GetTexture("_MainTex");
var x = -((bottomRight.x - topLeft.x) / columns) / tex.width;
var y = ((bottomRight.y - topLeft.y) / rows) / tex.height;
Vector4 a = new Vector4(axis.x, axis.y, axis.z, 0f);
Vector4 p = new Vector4(pivot.x, pivot.y, pivot.z, 0f);
Vector4 t = new Vector4(columns, rows, x, y);
asset.m_material.SetVector("_RollParams3", t);
asset.m_material.SetVector("_RollLocation0", p);
asset.m_material.SetVector("_RollParams0", a);
if (asset.m_lodMaterial)
{
    asset.m_lodMaterial.SetVector("_RollParams3", t);
    asset.m_lodMaterial.SetVector("_RollLocation0", p);
    asset.m_lodMaterial.SetVector("_RollParams0", a);
}
if (asset.m_lodMaterialCombined)
{
    asset.m_lodMaterialCombined.SetVector("_RollParams3", t);
    asset.m_lodMaterialCombined.SetVector("_RollLocation0", p);
    asset.m_lodMaterialCombined.SetVector("_RollParams0", a);
}
Vector3[] v = asset.m_mesh.vertices;
var c = asset.m_mesh.colors;
Color[] nc = new Color[v.Length];
for (int i = 0; i < v.Length; i++)
{
    nc[i] = new Color(c[i].r, c[i].g, 1 - ((1 - c[i].r) * strength), 1f);
}
asset.m_mesh.colors = nc;
if (asset.m_lodMesh)
{
    v = asset.m_lodMesh.vertices; c = asset.m_lodMesh.colors; nc = new Color[v.Length];
    for (int i = 0; i < v.Length; i++)
    {
        nc[i] = new Color(c[i].r, c[i].g, 1 - ((1 - c[i].r) * strength), 1f);
    }
    asset.m_lodMesh.colors = nc;
}

// Tells the asset editor to save _RollParams3, _RollLocation0 and _RollParams0 shader properties
var vectorProps = Type.GetType("ColossalFramework.Packaging.ShaderUtil, ColossalManaged").GetField("vectorProps").GetValue(null) as string[];
vectorProps[4] = "_RollParams3";
vectorProps[5] = "_RollLocation0";
vectorProps[6] = "_RollParams0";