d3d10/collada/buffer.py

from collections import defaultdict
from itertools import chain, islice
from typing import Dict, Tuple, List
from dataclasses import dataclass
import dataclasses

from collada import parse
from collada import types
from collada.util import find_semantics

def linearize_offset_table(by_offset, p_stride):
    for offset in range(p_stride):
        for input, source in by_offset[offset]:
            yield input, source

mesh_semantic_names = ["NORMAL", "TEXCOORD"]

def build_offset_table(collada, triangles, p_stride):
    vertex_input, = find_semantics(triangles.inputs, "VERTEX")
    vertices = collada.lookup(vertex_input.source, types.Vertices)
    position_input, = find_semantics(vertices.inputs, "POSITION")
    position_source = collada.lookup(position_input.source, types.SourceCore)
    assert type(position_source.array_element) is types.FloatArray

    by_offset = defaultdict(list)
    by_offset[vertex_input.offset].append((vertex_input, position_source))

    for semantic_name in mesh_semantic_names:
        for input in find_semantics(triangles.inputs, semantic_name):
            source = collada.lookup(input.source, types.SourceCore)
            assert type(source.array_element) is types.FloatArray
            by_offset[input.offset].append((input, source))

    assert len(triangles.p) == triangles.count * 3 * p_stride

    used_offsets = [i for i in range(p_stride) if i in by_offset]
    linearized_table = linearize_offset_table(by_offset, p_stride)
    return list(linearized_table), used_offsets

def mesh_vertex_index_buffer_triangles(collada, mesh, triangles):
    max_offset = max(i.offset for i in triangles.inputs)
    p_stride = max_offset + 1
    offset_table, used_offsets = build_offset_table(collada, triangles, p_stride)

from prettyprinter import pprint, install_extras
install_extras(include=["dataclasses"])

@dataclass
class MeshVertexIndexBufferState:
    index_buffer: List[int]

    def __init__(self):
        self.index_buffer = [] # a list of integers
        self.vertex_buffer = [] # a list of floats

        # vertex_index_table: input/collada vertex indices in the order written
        #                     to the index buffer
        #   indices: output vertex index (absolute)
        #   values: collada vertex index
        self.vertex_index_table = []

        # one offset table per <triangles>
        self.offset_tables = []

def mesh_vertex_index_buffer(collada, mesh):
    state = MeshVertexIndexBufferState()

    # index_table:
    #   keys: index_table_key
    #   values: index integer
    index_table = {}
    next_output_index = 0

    for triangles in mesh.primitive_elements:
        assert type(triangles) is types.Triangles

        max_offset = max(i.offset for i in triangles.inputs)
        p_stride = max_offset + 1
        offset_table, used_offsets = build_offset_table(collada, triangles, p_stride)
        state.offset_tables.append(offset_table)
        input_key = tuple(dataclasses.astuple(input) for input, source in offset_table)

        for vertex_ix in range(triangles.count * 3):
            offset_key = tuple(triangles.p[vertex_ix * p_stride + offset] for offset in used_offsets)
            index_table_key = tuple((input_key, offset_key))

            ######################################################################
            # append to the index buffer
            ######################################################################
            if index_table_key in index_table:
                state.index_buffer.append(index_table[index_table_key])
                continue
            index_table[index_table_key] = next_output_index
            state.index_buffer.append(next_output_index)
            next_output_index += 1

            ######################################################################
            # emit vertex attributes for new output index in vertex buffer
            ######################################################################
            for input, source in offset_table:
                p_index = triangles.p[vertex_ix * p_stride + input.offset]
                if input.semantic == "VERTEX":
                    state.vertex_index_table.append(p_index)

                source_stride = source.technique_common.accessor.stride
                source_index = p_index * source_stride
                assert type(source.array_element) is types.FloatArray
                array_slice = source.array_element.floats[source_index:source_index+source_stride]
                state.vertex_buffer.extend(array_slice)

    return state

def skin_vertex_buffer(collada, skin, vertex_index_table):
    max_offset = max(i.offset for i in skin.vertex_weights.inputs)
    joints_input, = find_semantics(skin.vertex_weights.inputs, "JOINT")
    joints_source = collada.lookup(joints_input.source, types.SourceCore)
    weights_input, = find_semantics(skin.vertex_weights.inputs, "WEIGHT")
    weights_source = collada.lookup(weights_input.source, types.SourceCore)
    assert weights_source.technique_common.accessor.stride == 1
    assert joints_source.technique_common.accessor.stride == 1

    vertex_weights = defaultdict(int)

    v_stride = max_offset + 1
    v_offset = 0
    vertex_influences = []
    for vcount in skin.vertex_weights.vcount:
        influences = []
        for vi in range(vcount):
            joint_index = skin.vertex_weights.v[v_offset + joints_input.offset]
            weight_index = skin.vertex_weights.v[v_offset + weights_input.offset]
            weight = weights_source.array_element.floats[weight_index]
            influences.append((joint_index, weight))
            v_offset += v_stride
        assert len(influences) <= 4, len(influences)
        vertex_influences.append(influences)

    ######################################################################
    # generate the joint/weight buffer
    ######################################################################

    vertex_buffer = []
    # vertex_index_table: input/collada vertex indices in the order written to the index buffer
    for vertex_index in vertex_index_table:
        influences = vertex_influences[vertex_index]
        def emit(column):
            for i in range(4):
                if i >= len(influences):
                    vertex_buffer.append(0)
                else:
                    vertex_buffer.append(influences[i][column])
        emit(0) # emit joint int4
        emit(1) # emit weight float4
    return vertex_buffer

if __name__ == "__main__":
    import sys
    collada = parse.parse_collada_file(sys.argv[1])

    mesh = collada.library_geometries[0].geometries[0].geometric_element
    assert type(mesh) is types.Mesh
    state = mesh_vertex_index_buffer(collada, mesh)

    #skin = collada.library_controllers[0].controllers[0].control_element
    #assert type(skin) is types.Skin
    #vertex_buffer_jw = skin_vertex_buffer(collada, skin, vertex_index_table)