feat(文件拆分): 拆分字体图像基础能力

internal/base/image/storage.go

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+// 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 image
+
+import "image"
+
+// StorageCost 预留十六位像素空间，并计入编码、调色板与底层像素缓冲容量
+// 包装图像可实现BackingImage() image.Image，使底层共享缓冲计入预算
+// 入参: img 图片资源, limit 缓存预算
+// 返回: int 估算字节数或超预算标记
+func StorageCost(img image.Image, limit int) int {
+	cost := 256
+	w, h := img.Bounds().Dx(), img.Bounds().Dy()
+	if limit < cost || w <= 0 || h <= 0 || w > (limit-cost)/8/h {
+		return limit + 1
+	}
+	pixels := w * h * 8
+	if encoded, ok := img.(*EncodedImage); ok {
+		if cap(encoded.data) > limit-cost-pixels {
+			return limit + 1
+		}
+		return cost + pixels + cap(encoded.data)
+	}
+	var buffers [5]int
+	switch source := img.(type) {
+	case *image.RGBA:
+		buffers[0] = cap(source.Pix)
+	case *image.RGBA64:
+		buffers[0] = cap(source.Pix)
+	case *image.NRGBA:
+		buffers[0] = cap(source.Pix)
+	case *image.NRGBA64:
+		buffers[0] = cap(source.Pix)
+	case *image.Gray:
+		buffers[0] = cap(source.Pix)
+	case *image.Gray16:
+		buffers[0] = cap(source.Pix)
+	case *image.Alpha:
+		buffers[0] = cap(source.Pix)
+	case *image.Alpha16:
+		buffers[0] = cap(source.Pix)
+	case *image.CMYK:
+		buffers[0] = cap(source.Pix)
+	case *image.Paletted:
+		if cap(source.Palette) > (limit-cost)/16 {
+			return limit + 1
+		}
+		buffers[0], buffers[1] = cap(source.Pix), cap(source.Palette)*16
+	case *image.YCbCr:
+		buffers = [5]int{cap(source.Y), cap(source.Cb), cap(source.Cr)}
+	case *image.NYCbCrA:
+		buffers = [5]int{cap(source.Y), cap(source.Cb), cap(source.Cr), cap(source.A)}
+	case *planarTIFFImage:
+		if cap(source.palette) > (limit-cost)/8 {
+			return limit + 1
+		}
+		cost += cap(source.palette) * 8
+		if cap(source.planes) > (limit-cost)/16 || len(source.planes) > len(buffers) {
+			return limit + 1
+		}
+		cost += cap(source.planes) * 16
+		for i, plane := range source.planes {
+			switch plane := plane.(type) {
+			case *image.Gray:
+				buffers[i] = cap(plane.Pix)
+			case *image.Gray16:
+				buffers[i] = cap(plane.Pix)
+			default:
+				buffers[i] = StorageCost(plane, limit-cost)
+			}
+		}
+	case *tiffFaxImage:
+		if cap(source.blocks) > (limit-cost)/16 {
+			return limit + 1
+		}
+		cost += cap(source.blocks) * 16
+		for _, block := range source.blocks {
+			size := StorageCost(block, limit-cost)
+			if size > limit-cost {
+				return limit + 1
+			}
+			cost += size
+		}
+	case *orientedTIFFImage:
+		buffers[0] = StorageCost(source.source, limit-cost)
+	case *maskedTIFFImage:
+		buffers[0] = StorageCost(source.source, limit-cost)
+		buffers[1] = StorageCost(source.mask, limit-cost)
+	case *transparentEdgeImage:
+		buffers[0] = StorageCost(source.source, limit-cost)
+	case *transparentEdgeImage64:
+		buffers[0] = StorageCost(source.source, limit-cost)
+	case interface{ BackingImage() image.Image }:
+		buffers[0] = StorageCost(source.BackingImage(), limit-cost)
+	}
+	storage := 0
+	for _, size := range buffers {
+		if size > limit-cost-storage {
+			return limit + 1
+		}
+		storage += size
+	}
+	if pixels > limit-cost {
+		return limit + 1
+	}
+	return cost + max(pixels, storage)
+}