transfer_function_example.rst

Transfer Functions¶

In [1]:

import example_utils
from vapor import session, renderer, dataset, camera, utils, transferfunction

ses = session.Session()
data = example_utils.OpenExampleDataset(ses)

ren = data.NewRenderer(renderer.VolumeRenderer)
ses.GetCamera().LookAt((32, 120, 120), (32, 32, 32))
ses.Show()

Warning: sysroot "/Applications/Xcode_12.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk" not found (ignoring for now).

Vapor 3.9.2
Python 3.9.19 (/Users/pearse/miniconda3/envs/readTheDocs)
OpenGL 4.1 Metal - 83.1

UNSUPPORTED (log once): POSSIBLE ISSUE: unit 3 GLD_TEXTURE_INDEX_3D is unloadable and bound to sampler type (Float) - using zero texture because texture unloadable

We created a volume rendering however it is fully opaque. We can use a transfer function to adjust the visible portions. Before we adjust the opacity map of the TF, we get a histogram to help us determine what we want to hide.

In [2]:

utils.ShowMatPlotLibHistogram(ses, ren)

Usually we want to hide the most common value so below we construct an opacity map that accomplishes this.

In [3]:

# List of x,y pairs where x is the data value and y is the opacity for that data value
opacities = [(-0.3, 1), (-0.1, 0), (0.1, 0), (0.3, 1)]

We can get the matplotlib histogram plot and add our opacity map to it to compare.

In [4]:

plt = utils.GetMatPlotLibHistogram(ses, ren)
plt.plot(*zip(*opacities))
plt.show()

Now we apply the map to the transfer function

In [5]:

# Renderers can have multiple transfer functions.
# GetPrimaryTransferFunction returns the one that is usually the most useful.
# You can use `tf.GetTransferFunction(var_name)` to get other transfer functions.
tf = ren.GetPrimaryTransferFunction()
tf.SetOpacityControlPoints(opacities)
ses.Show()

You can adjust the colormap in a similar fashion. Use help(tf) for more information. Vapor includes a list of built-in colormaps and these can be applied with tf.LoadBuiltinColormap(name)

Builtin Colormaps¶

In [6]:

tf.LoadBuiltinColormap("Sequential/BlackBodyExtended")
ses.Show()

List of All Builtin Colormaps¶

In [7]:

ses.DeleteRenderer(ren)
ren = data.NewRenderer(renderer.TwoDDataRenderer)
tf = ren.GetPrimaryTransferFunction()

for cmap in transferfunction.TransferFunction.ListBuiltinColormaps():
    tf.LoadBuiltinColormap(cmap)

    print(cmap)
    tf.ShowMatPlotLibColorbar()

Highlighting/topo

Highlighting/oxy

Diverging/tarn

Diverging/curl

Diverging/CoolWarmSmooth

Diverging/PurpleWhiteOrange

Diverging/diff

Diverging/GreenWhiteRed

Diverging/CoolWarmBent

Diverging/BlueWhiteGold

Diverging/CoolWarm

Diverging/GreenWhitePurple

Diverging/balance

Diverging/delta

Sequential/BlackBody

Sequential/thermal

Sequential/tempo

Sequential/speed

Sequential/Kindlmann

Sequential/KindlmannExtended

Sequential/algae

Sequential/deep

Sequential/haline

Sequential/turbid

Sequential/rain

Sequential/Rainbow

Sequential/phase

Sequential/BlackBodyExtended

Sequential/dense

Sequential/amp

Sequential/ice

Sequential/matter

Sequential/BlackWhite

Sequential/solar