Allows fury to deal with Uniforms in shaders and change them dynamically

[devmessias]

An uniform variable should be chosen when we have any kind of information which act as constants, at least during the draw call.

This commit implements the following behaviors: 1 - avoids creating an observable-vtk for each uniform variable 2 - allows the update of an uniform variable dynamically

Here it's a simple example

markerUniforms = [
        Uniform(name='edgeColor', type='3f', value=edgeColor),
        Uniform(name='edgeWidth', type='f', value=edgeWidth),
        Uniform(name='edgeOpacity', type='f', value=edgeOpacity),
        Uniform(name='markerOpacity', type='f', value=markerOpacity),
    ]
CustomUniforms = Uniforms(markerUniforms)
observerId = add_shader_callback(
            sq_actor, CustomUniforms)
CustomUniforms.observerId = observerId
sq_actor.CustomUniforms = CustomUniforms

sq_actor.CustomUniforms.edgeWidth = 0.5

[pep8speaks]

Hello @devmessias! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file fury/shaders/__init__.py:

Line 5:76: W291 trailing whitespace

• In the file fury/shaders/base.py:

Line 207:64: W291 trailing whitespace

Comment last updated at 2021-04-26 23:08:44 UTC

[devmessias]

Here is an example of a shader actor with those modifications

# marker billboard from pull #422 using this new Uniform API
nodes_actor = actor.marker_billboard(
    centers,
    markers=markers,
    edgeWidth=edgeWidth,
    edgeColor=edgeColor.data,
    colors=colors,
    scales=.1,
)

scene = window.Scene()
scene.add(nodes_actor)
interactive = True


showm = window.ShowManager(scene,
                           size=(900, 768), reset_camera=False,
                           order_transparent=True)


showm.initialize()

counter = itertools.count()
def timer_callback(obj, event):
    nodes_actor.CustomUniforms.edgeWidth.value = np.random.choice([0.2, 1, 0.5])
    nodes_actor.CustomUniforms.edgeColor.value = np.random.randint(0, 255, size=3)
    cnt = next(counter)
    showm.render()
    if cnt == 100:
        showm.exit()

showm.add_timer_callback(True, 200, timer_callback)
showm.start()

[devmessias]

Hi @devmessias,

Could you add some unit tests? Also, can you complete the documentation? Last point, can you switch from C/C++ style to python style concerning variable/class names. Global comment for all your PR. Thank you !

Yes, of course! I'll do it.