Adding decals to terrain

Hi, all!

I need to add decal to terrain at Vector3 pos location and Vector3 normal.
How can I

  1. Find closest terrain patch to pos and use it as drawable. is there some way?
    I don’t want to use raycast as I already know the location.

  2. Find the rotation from normal vector.

I think you need to use the search function. I think most of the questions you raised existed in the forum.
There is a decal example in the lib.
I remember there are a few other solutions including a car wheel trace mark kindly shared by a member a year or two ago.
Also see the basic effect posted by Lumak. I believed it has decal effect in there.


Decal example use Raycast which provides the Drawable.
And there’s no decal examples I am aware of on the forum.

as for Lumak’s code, he creates geometry, not uses decals in offroad vehicle demo.

George1 refers to a decal example in the lib, here:

If you only want to find the nearest TerrainPatch, you could calc that using the Terrain API (*possibly, depending; or other Drawable methods):

@jmiller would you please read what I write before answering? :slight_smile:

I wrote exactly about 08_Decals and that it uses Raycast to get Drawable.

About terrain API - it is not obvoius how to get TerrainPatch closest to a point,
so I still wait for help with this.

My bad – I was tired and completely missed your first sentence. :slight_smile:

As an example of ‘other Drawable methods’: could iterate patches and use their Drawable::GetWorldBoundingBox().Center() perhaps?

By ‘calc’, I was thinking of a simpler 2D method that may or may not be suitable. by analogy: “given the position of a grid (terrain), and the grid square (patch) size, find which grid coord a point falls in”.

If you know the normal vector and the position , you can get a rotation vector using a vector function from irrlicht :

Vector3 Vector3::EulerFromNormal()
Vector3 angle;
angle.y_ = (atan2(x_ , z_) * :M_RADTODEG);
if (angle.y_ < 0) angle.y_ += 360;
if (angle.y_ >= 360) angle.y_ -= 360;

float z1 = sqrt(x_ * x_ + z_ * z_);
    angle.x_ = (atan2(z1, y_) * M_RADTODEG - 90.0f);

    if (angle.x_ < 0)  angle.x_ += 360;
    if (angle.x_ >= 360) angle.x_ -= 360;

    return angle;


Please note : Depending on your culling (CW , CCW) you may need to negate the normal to get the correct rotation.
Build a Quaternion using the returned vector (Quaternion rot(returned.x_ , returned,y_ , returned.z_);

@jmiller - I know I can get height on the terrein in any point, can’t this be converted to patch somehow?
the iteratiom method is last resort, it is very, very slow.
About 2D - one can get texture coordinate too. I don’t understand why there’s no easy Drawable access :frowning:

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