vpClassifyScalars(3)

💖 vpClassifyScalars(3) 💖

okay bestie, so this is a library functions manual page for vpClassifyScalars(3), and it's literally the shortcut queen of the VolPack world. let's get into it 🫶

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✨ NAME ✨

vpClassifyScalars — create a preclassified volume from scalar data. that's it, that's the whole vibe. 🎀

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🌸 SYNOPSIS 🌸

#include <volpack.h>

vpResult
vpClassifyScalars(vpc, scalar_data, length, scalar_field,
        gradient_field, norm_field)
    vpContext *vpc;
    unsigned char *scalars;
    int size;
    int scalar_field, gradient_field, norm_field;

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🦋 ARGUMENTS 🦋

• vpc — the VolPack context you got from vpCreateContext. your main character.
• scalar_data — a 3D array holding one 8-bit scalar value for each voxel in the volume. every voxel gets exactly one lil byte, no more no less.
• length — size of scalar_data in bytes. yes, bytes. 👑
• scalar_field — field number identifying a voxel field for storing the scalar value.
• gradient_field — field number identifying a voxel field for storing the gradient magnitude of the scalar value.
• norm_field — field number identifying a voxel field for storing the surface normal vector for the voxel.

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💅 DESCRIPTION 💅

vpClassifyScalars is giving combo move energy: it smooshes together the functionality of vpVolumeNormals and vpClassifyVolume so you can produce a preclassified volume directly from a 3D array of scalar values — no 3D voxel array needed. periodt.

it's highkey made for preparing large data sets for rendering with a fixed classification function, especially when the 3D voxel array would be too big to fit in main memory. like, if it doesn't fit, this is your girl. 💖

the primary limitation (and bestie, we must talk about it): the only fields each voxel may contain are the fields produced by vpVolumeNormals — that's an 8-bit scalar value, and an 8-bit gradient and/or a 16-bit surface normal vector. that's the whole menu, no substitutions.

also, if you want to process one scanline of a scalar array at a time instead, go look at vpClassifyScanline. 🌈

how to actually use it, step by step 🧚

1. first, define the volume size, voxel size, and voxel fields exactly like you would before calling vpVolumeNormals.
2. however — and this is the slay part — there is no need to call vpSetRawVoxels. skip it. not needed. 🙈
3. also define the opacity transfer function (see vpSetClassifierTable(3)).
4. then call vpClassifyScalars with the same arguments you would use for vpVolumeNormals — peep vpVolumeNormals(3) for more details.
5. the result is a preclassified volume, as described in vpClassifyVolume(3). iconic.

if a voxel array has been declared, it is not used or modified. it's just sitting there, unbothered, moisturized, in its lane. 💅

⚠️ heads up: any existing preclassified volume data is destroyed. gone. say bye. 💀

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⭐ STATE VARIABLES ⭐

you can retrieve info about the current preclassified volume with these state variable codes (see vpGeti(3)):

• VP_VIEW_X_SIZE
• VP_VIEW_Y_SIZE
• VP_VIEW_Z_SIZE
• VP_VIEW_X_AXIS
• VP_VIEW_Y_AXIS
• VP_VIEW_Z_AXIS

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😭 ERRORS 😭

the normal return value is VP_OK. but sometimes things go sideways, and these are the possible error return values:

• VPERROR_BAD_VOXEL — the voxel size or the voxel fields have not been specified, or have been incorrectly specified. bestie. you forgot a step.
• VPERROR_BAD_CLASSIFIER — the opacity transfer function tables have invalid sizes, or are associated with invalid voxel fields, or have been incorrectly specified. the classifier said no. 🙈

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👑 SEE ALSO 👑

VolPack(3), vpCreateContext(3), vpVolumeNormals(3), vpSetClassifierTable(3), vpClassifyVolume(3), vpClassifyScanline(3)

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that's the whole page, bestie, no cap 💜 this came out of the VolPack library — volume rendering royalty — and it's the vpClassifyScalars(3) page, so if you ever forget, just remember: VolPack, vpClassifyScalars(3), and you're set. slay, go classify some scalars. ✨🦋🌸