Varying Color

This example shows how to use shaders to generate a shaded output. We will demonstrate how to load polydata then use a custom shader calls to render a custom shaded model. First, a bunch of imports.

from fury import io, ui, utils, window
from fury.data.fetcher import fetch_viz_models, read_viz_models
from fury.shaders import add_shader_callback, shader_to_actor

Let’s download and load the model

fetch_viz_models()
model = read_viz_models('utah.obj')

Dataset is already in place. If you want to fetch it again please first remove the folder /Users/skoudoro/.fury/models

Let’s start by loading the polydata of choice. For this example we use the standard utah teapot model. currently supported formats include OBJ, VTK, FIB, PLY, STL and XML

utah = io.load_polydata(model)
utah = utils.get_polymapper_from_polydata(utah)
utah = utils.get_actor_from_polymapper(utah)
mapper = utah.GetMapper()

To change the default shader we add a shader replacement. Specify vertex shader using vtkShader.Vertex Specify fragment shader using vtkShader.Fragment

vertex_shader_code_decl = """
    out vec4 myVertexVC;
    """

vertex_shader_code_impl = """
    myVertexVC = vertexMC;
    """

fragment_shader_code_decl = """
    uniform float time;
    varying vec4 myVertexVC;
    """

fragment_shader_code_impl = """
    vec2 iResolution = vec2(1024,720);
    vec2 uv = myVertexVC.xy/iResolution;
    vec3 col = 0.5 + 0.5 * cos((time/30) + uv.xyx + vec3(0, 2, 4));
    fragOutput0 = vec4(col, fragOutput0.a);
    """

shader_to_actor(
    utah, 'vertex', impl_code=vertex_shader_code_impl, decl_code=vertex_shader_code_decl
)
shader_to_actor(utah, 'fragment', decl_code=fragment_shader_code_decl)
shader_to_actor(utah, 'fragment', impl_code=fragment_shader_code_impl, block='light')

Let’s create a scene.

scene = window.Scene()

global timer
timer = 0

The timer will call this user defined callback every 30 milliseconds.

def timer_callback(obj, event):
    global timer
    timer += 1.0
    showm.render()
    scene.azimuth(5)

The shader callback will update the color of our utah pot via the update of the timer variable.

def shader_callback(_caller, _event, calldata=None):
    program = calldata
    global timer
    if program is not None:
        try:
            program.SetUniformf('time', timer)
        except ValueError:
            pass


add_shader_callback(utah, shader_callback)

1

Let’s add a textblock to the scene with a custom message

tb = ui.TextBlock2D()
tb.message = 'Hello Shaders'

Show Manager

Now that all the elements have been initialised, we add them to the show manager.

current_size = (1024, 720)
showm = window.ShowManager(scene, size=current_size, reset_camera=False)


showm.add_timer_callback(True, 30, timer_callback)

scene.add(utah)
scene.add(tb)

interactive = False
if interactive:
    showm.start()

window.record(showm.scene, size=current_size, out_path='viz_shader.png')