How does UV mapping work with surfacetool in Godot?

Question

I'm coding a terrain generator in Godot. I generate the Mesh using SurfaceTool and triangle strips. The geometry works fine — but the UV mapping doesn't, as each triangle repeats the texture instead of the full mesh covering the texture once:

Normalizing the UV-Coordinates to fit into the 0,0 - 1,1 dimensions is what should work, but doesn't, as it makes only one pair of triangles have the full texture and the rest is blank:

extends MeshInstance

export var terrain_width = 16
export var terrain_depth = 16
export var terrain_height = 1
export var terrain_scale = 1

#Noise Generation
var terrain_noise = OpenSimplexNoise.new()

var terrain_heightmap = ImageTexture.new()
var terrain_texture = Texture.new()
var terrain_material = SpatialMaterial.new()
var terrain_mesh = Mesh.new()

var surfacetool = SurfaceTool.new()

func _ready():
    generate_heightmap()
    generate_mesh()

func generate_heightmap():
    #Setup the noise
    terrain_noise.seed = randi()
    terrain_noise.octaves = 4
    terrain_noise.period = 20.0
    terrain_noise.persistence = 0.8

    #Make the texture
    terrain_heightmap.create_from_image(terrain_noise.get_image(terrain_width+1, terrain_depth+1))
    terrain_texture = terrain_heightmap

func generate_mesh():
    #Set the material texture to the heightmap
    terrain_material.albedo_texture = terrain_texture

    # This is where the uv-mapping occurs, via the add_uv function
    for z in range(0,terrain_depth):
        surfacetool.begin(Mesh.PRIMITIVE_TRIANGLE_STRIP)
        for x in range(0,terrain_width):

            surfacetool.add_uv(Vector2((terrain_width-x)/terrain_width,z/terrain_depth))
            surfacetool.add_vertex(Vector3((terrain_width-x)*terrain_scale, terrain_noise.get_noise_2d(x,z)*terrain_height*terrain_scale, z*terrain_scale))
            surfacetool.add_uv(Vector2((terrain_width-x)/terrain_width,(z+1)/terrain_depth))
            surfacetool.add_vertex(Vector3((terrain_width-x)*terrain_scale, terrain_noise.get_noise_2d(x,z+1)*terrain_height*terrain_scale, (z+1)*terrain_scale))

        surfacetool.generate_normals()
        surfacetool.index()

        surfacetool.commit(terrain_mesh)

    #Set the texture and mesh on the MeshInstance
    self.material_override = terrain_material
    self.set_mesh(terrain_mesh)
    self.set_surface_material(0, terrain_texture)

I expect each triangle to cover only the corresponding coordinates in the texture. It seems as if each triangle is considered as a separate surface.

score 1 · Answer 1 · answered May 02 '19 at 18:20

You have lots of integer divisions there. There are many ways to fix that. Here's a quick one: Just add .0 after your exported variable's default values:

export var terrain_width  = 16.0
export var terrain_depth  = 16.0
export var terrain_height = 1.0
export var terrain_scale  = 1.0

And here's a more explicit way:

export(float) var terrain_width  = 16
export(float) var terrain_depth  = 16
export(float) var terrain_height = 1
export(float) var terrain_scale  = 1

Assuming you don't have any other bugs, this should fix the issue.

How does UV mapping work with surfacetool in Godot?

1 Answers1