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 window, ui, io, utils
import vtk

Let’s download and load the model

from fury.data.fetcher import fetch_viz_models, read_viz_models
fetch_viz_models()
model = read_viz_models('utah.obj')

Out:

Dataset is already in place. If you want to fetch it again please first remove the folder /Users/koudoro/.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, VKT, 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

mapper.AddShaderReplacement(
    vtk.vtkShader.Vertex,
    "//VTK::ValuePass::Dec",
    True,
    """
    //VTK::ValuePass::Dec
    out vec4 myVertexVC;
    """,
    False
)

mapper.AddShaderReplacement(
    vtk.vtkShader.Vertex,
    "//VTK::ValuePass::Impl",
    True,
    """
    //VTK::ValuePass::Impl
    myVertexVC = vertexMC;
    """,
    False
)

mapper.AddShaderReplacement(
    vtk.vtkShader.Fragment,
    "//VTK::Light::Dec",
    True,
    """
    //VTK::Light::Dec
    uniform float time;
    varying vec4 myVertexVC;
    """,
    False
)


mapper.AddShaderReplacement(
    vtk.vtkShader.Fragment,
    '//VTK::Light::Impl',
    True,
    """
    //VTK::Light::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, 1.0);
    """,
    False
)

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)

We can use a decorator to callback to the shader.

@window.vtk.calldata_type(window.vtk.VTK_OBJECT)
def vtk_shader_callback(caller, event, calldata=None):
    program = calldata
    global timer
    if program is not None:
        try:
            program.SetUniformf("time", timer)
        except ValueError:
            pass

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

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

Change the property of the actor

utah.GetProperty().SetOpacity(0.5)

Invoke callbacks to any VTK object

mapper.AddObserver(window.vtk.vtkCommand.UpdateShaderEvent,
                   vtk_shader_callback)

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.initialize()
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")