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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 | 1724x 1724x 1724x 1724x 1718x 6x 6x 6x 18x 18x 18x 18x 17x 1x 17x 33x 33x 4x 29x 13x 1x | import addAllToArray from "../Core/addAllToArray.js";
import defined from "../Core/defined.js";
import Frozen from "../Core/Frozen.js";
import WebGLConstants from "../Core/WebGLConstants.js";
/**
* Get an array of primitives for a given mesh. If the EXT_mesh_primitive_restart extension is present, use it to combine groups of primitives.
* If the extension is not present or its spec is violated, return the original mesh.primitives.
* @param {object} mesh A mesh from the glTF meshes array
* @returns {object[]} An array of mesh primitives
* @private
*/
function getMeshPrimitives(mesh) {
const meshExtensions = mesh.extensions ?? Frozen.EMPTY_OBJECT;
const primitiveRestartExtension = meshExtensions.EXT_mesh_primitive_restart;
const meshPrimitives = mesh.primitives;
if (!defined(primitiveRestartExtension)) {
return meshPrimitives;
}
// Note: per the spec, any violation of the extension's specification should cause us to fall back to mesh.primitives, if detecting the violation is feasible.
// Start with a copy of mesh.primitives. For each group, replace the first primitive in the group with a primitive representing the entire group,
// and set the rest of the primitives in the group to `undefined`.
// This allows us to identify which remaining primitives do not use primitive restart, and any errors involving a primitive appearing in more than one group.
const primitives = [];
addAllToArray(primitives, meshPrimitives);
for (const group of primitiveRestartExtension.primitiveGroups) {
// Spec: the group must not be empty and all indices must be valid array indices into mesh.primitives.
const firstPrimitiveIndex = group.primitives[0];
Iif (!defined(firstPrimitiveIndex) || !meshPrimitives[firstPrimitiveIndex]) {
return meshPrimitives;
}
const primitive = {
...meshPrimitives[firstPrimitiveIndex],
indices: group.indices,
};
// Spec: primitive restart only supported for these topologies.
switch (primitive.mode) {
case WebGLConstants.TRIANGLE_FAN:
case WebGLConstants.TRIANGLE_STRIP:
case WebGLConstants.LINE_STRIP:
case WebGLConstants.LINE_LOOP:
break;
default:
return meshPrimitives;
}
for (const primitiveIndex of group.primitives) {
const thisPrimitive = primitives[primitiveIndex];
// Spec: all primitives must use indexed geometry and a given primitive may appear in at most one group.
// Spec: all primitives must have same topology.
if (
!defined(thisPrimitive?.indices) ||
thisPrimitive.mode !== primitive.mode
) {
return meshPrimitives;
}
primitives[primitiveIndex] = undefined;
}
primitives[firstPrimitiveIndex] = primitive;
}
return primitives.filter(defined);
}
export default getMeshPrimitives;
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