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')

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)

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')