Cut terrain to circle?

[Uther]

Hello i have question with panda3d, can i cut terrain ?
by default when I load a terrain it has the shape of a square, can i cut this terrain for generate circle ?

i want use this heightmap :

with 2 terrain for generate planete, but i have square, i want to “transform” square to circle

my python code, besed of panda3d sample

#!/usr/bin/env python

from direct.showbase.ShowBase import ShowBase
from panda3d.core import ShaderTerrainMesh, Shader, load_prc_file_data
from panda3d.core import SamplerState


class ShaderTerrainDemo(ShowBase):
    def __init__(self):

        # Load some configuration variables, its important for this to happen
        # before the ShowBase is initialized
        load_prc_file_data("", """
            textures-power-2 none
            gl-coordinate-system default
            window-title Panda3D ShaderTerrainMesh Demo
        """)

        # Initialize the showbase
        ShowBase.__init__(self)

        # Increase camera FOV as well as the far plane
        self.camLens.set_fov(90)
        self.camLens.set_near_far(0.1, 50000)

        # Construct the terrain
        self.terrain_node = ShaderTerrainMesh()

        # Set a heightfield, the heightfield should be a 16-bit png and
        # have a quadratic size of a power of two.
        self.terrain_node.heightfield = self.loader.loadTexture("heightfield.png")

        # Set the target triangle width. For a value of 10.0 for example,
        # the terrain will attempt to make every triangle 10 pixels wide on screen.
        self.terrain_node.target_triangle_width = 10.0

        # Generate the terrain
        self.terrain_node.generate()

        # Attach the terrain to the main scene and set its scale. With no scale
        # set, the terrain ranges from (0, 0, 0) to (1, 1, 1)
        self.terrain = self.render.attach_new_node(self.terrain_node)
        self.terrain.set_scale(1024, 1024, 100)
        self.terrain.set_pos(-512, -512, -70.0)

        # Set a shader on the terrain. The ShaderTerrainMesh only works with
        # an applied shader. You can use the shaders used here in your own application
        terrain_shader = Shader.load(Shader.SL_GLSL, "terrain.vert.glsl", "terrain.frag.glsl")
        terrain_shader = Shader.load(Shader.SL_GLSL, "terrain.vert.glsl", "terrain_tex_f.glsl")
        self.terrain.set_shader(terrain_shader)
        
        
        
        
        # Construct the terrain
        self.terrain_node2 = ShaderTerrainMesh()

        # Set a heightfield, the heightfield should be a 16-bit png and
        # have a quadratic size of a power of two.
        self.terrain_node2.heightfield = self.loader.loadTexture("heightfield.png")

        # Set the target triangle width. For a value of 10.0 for example,
        # the terrain will attempt to make every triangle 10 pixels wide on screen.
        self.terrain_node2.target_triangle_width = 10.0

        # Generate the terrain
        self.terrain_node2.generate()

        # Attach the terrain to the main scene and set its scale. With no scale
        # set, the terrain ranges from (0, 0, 0) to (1, 1, 1)
        self.terrain2 = self.render.attach_new_node(self.terrain_node2)
        self.terrain2.set_scale(1024, 1024, 100)
        self.terrain2.set_pos(-512, 512, -70.0)
        self.terrain2.setHpr(0,180,0)

        # Set a shader on the terrain. The ShaderTerrainMesh only works with
        # an applied shader. You can use the shaders used here in your own application
        self.terrain2.set_shader(terrain_shader)
        
        
        
        
        
        self.terrain.set_shader_input("camera", self.camera)
        self.terrain2.set_shader_input("camera", self.camera)
        # Shortcut to view the wireframe mesh
        self.accept("f3", self.toggleWireframe)

ShaderTerrainDemo().run()

[rdb]

This could easily be done by discarding fragments. For example, to cut out a pure circle, add this to the top of the fragment shader’s main() function:

  vec2 from_center = terrain_uv - vec2(0.5);
  if (dot(from_center, from_center) > 0.25) {
    discard;
  }

Change 0.25 to alter the radius of the circle.

Or, you could discard all fragments that are entirely black in the heightmap, using something like this:

  float height = texture(ShaderTerrainMesh.heightfield, terrain_uv).x;
  if (height <= 0.0) {
    discard;
  }

[Uther]

thank you very musch it’s work

final render :

There is a small problem to join the 2 maps but I weigh that it comes from my heightmap image

[rdb]

If you’re trying to do planetary rendering, this is not the best approach, because the distortion is worst along the seams as you’ve noticed.

Instead, I would suggest that you take a normal heightmap, and change the vertex shader to interpret the coordinates as polar coordinates to map them to a sphere.

[Uther]

If you’re trying to do planetary rendering

Yes

@rdb

I would suggest that you take a normal heightmap, and change the vertex shader to interpret the coordinates as polar coordinates to map them to a sphere.

I don’t understand your solution, you mean with only 1 heightmap and only 1 terrain I can make a platenet?
like this :

[rdb]

Yes, though it would appear that ShaderTerrainMesh is not very well suited for this. It would be possible to create a sphere model with UV coordinates that map a heightmap to it (similar to the Mercator projection), and use that for sampling the height in the shader. Instead of the height affecting the z of each vertex, it would affect the distance between the vertex to the sphere’s centre.

[Uther]

In panda3d for create heightmap with affect z axis i use :
self.terrain_node.heightfield

for affect the sphere centre, what function must be use ?