feat(文件拆分): 拆分几何三维基础能力

internal/base/threed/u3d_resource_reader.go

@@ -0,0 +1,141 @@
+// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package threed
+
+import (
+	"fmt"
+	"math"
+	"unicode/utf8"
+)
+
+// u3dResourceReader 读取骨骼权重与动作资源中交错的普通字段和压缩字段
+type u3dResourceReader struct {
+	values  *u3dValues
+	decoder *u3dDecoder
+	bits    *u3dBits
+	hist    [8]u3dHistogram
+	charged uint64
+}
+
+// value 读取指定上下文的压缩字段，首次使用时初始化算术区间
+// 入参: context 压缩上下文, small 是否为8位字段
+// 返回: uint32 字段值
+func (r *u3dResourceReader) value(context int, small bool) uint32 {
+	if r.err() != nil {
+		return 0
+	}
+	if r.decoder.plain {
+		if small {
+			return uint32(r.values.u8())
+		}
+		return r.values.u32()
+	}
+	if r.bits == nil {
+		r.bits = newU3DBits(r.values.data[r.values.pos:])
+		r.bits.reserve = func(count, size uint64) error {
+			if err := r.decoder.reserve(count, size); err != nil {
+				return err
+			}
+			r.charged += count * size
+			return nil
+		}
+	}
+	return r.bits.dynamicValue(&r.hist[context], small)
+}
+
+// u32 读取普通32位字段，压缩开始后沿用当前算术区间
+// 返回: uint32 字段值
+func (r *u3dResourceReader) u32() uint32 {
+	if r.bits != nil {
+		return r.bits.u32()
+	}
+	return r.values.u32()
+}
+
+// f32 读取有限单精度数值
+// 返回: float32 字段值
+func (r *u3dResourceReader) f32() float32 {
+	value := math.Float32frombits(r.u32())
+	if !finite(float64(value)) && r.err() == nil {
+		r.values.err = fmt.Errorf("invalid U3D floating-point value")
+	}
+	return value
+}
+
+// text 读取UTF-8名称，压缩开始后逐字节解码而不重置区间
+// 返回: string 名称
+func (r *u3dResourceReader) text() string {
+	if r.err() != nil {
+		return ""
+	}
+	if r.bits == nil {
+		return r.values.text()
+	}
+	length := int(r.bits.byteValue()) | int(r.bits.byteValue())<<8
+	if r.err() != nil {
+		return ""
+	}
+	if err := r.decoder.reserve(uint64(length), 2); err != nil {
+		r.values.err = err
+		return ""
+	}
+	data := make([]byte, length)
+	for index := range data {
+		if index%1024 == 0 {
+			if err := r.decoder.ctx.Err(); err != nil {
+				r.values.err = err
+				return ""
+			}
+		}
+		data[index] = r.bits.byteValue()
+	}
+	if r.err() == nil && !utf8.Valid(data) {
+		r.values.err = fmt.Errorf("invalid U3D UTF-8 string")
+	}
+	return string(data)
+}
+
+// err 返回字段或算术解码错误
+// 返回: error 读取错误
+func (r *u3dResourceReader) err() error {
+	if r.values.err != nil {
+		return r.values.err
+	}
+	if r.bits != nil {
+		return r.bits.err
+	}
+	return nil
+}
+
+// done 校验末尾冲刷字段和块边界
+// 返回: error 读取或多余数据错误
+func (r *u3dResourceReader) done() error {
+	if err := r.err(); err != nil {
+		return err
+	}
+	if r.bits != nil {
+		if err := r.bits.finish(); err != nil {
+			return err
+		}
+		r.values.pos = len(r.values.data)
+	}
+	return r.values.done()
+}
+
+// release 归还当前块压缩上下文占用的临时预算
+func (r *u3dResourceReader) release() {
+	r.decoder.remaining += r.charged
+	r.charged = 0
+}