feat(压缩能力): 接入分级压缩优化窄屏布局

ofdgo_compression_images.go

@@ -0,0 +1,116 @@
+// 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 ofdgo
+
+import (
+	"context"
+	"fmt"
+	"image"
+	"math"
+	"strings"
+)
+
+// compressionImages 记录图片各处使用的最大像素需求
+type compressionImages struct {
+	ctx   context.Context
+	dpi   int
+	sizes map[string]image.Point
+}
+
+// compressionImageSize 将毫米显示尺寸换算为像素，非法尺寸不降采样
+// 入参: width 显示宽度, height 显示高度, dpi 分辨率上限
+// 返回: image.Point 像素需求
+func compressionImageSize(width, height float64, dpi int) image.Point {
+	w, h := math.Ceil(width*float64(dpi)/25.4), math.Ceil(height*float64(dpi)/25.4)
+	if w <= 0 || h <= 0 || math.IsNaN(w) || math.IsNaN(h) || math.IsInf(w, 0) || math.IsInf(h, 0) || w > 1<<30 || h > 1<<30 {
+		return image.Point{}
+	}
+	return image.Pt(int(w), int(h))
+}
+
+// compressionImageSizes 按正文、模板及注解的实际变换汇总共享图片尺寸
+// 入参: ctx 取消上下文, images 图片资源, dpi 分辨率上限
+// 返回: map[string]image.Point 资源像素需求, error 取消错误
+func (r *Reader) compressionImageSizes(ctx context.Context, images []ImageInfo, dpi int) (map[string]image.Point, error) {
+	if dpi == 0 {
+		return nil, nil
+	}
+	count, err := r.PageCount()
+	if err != nil {
+		return nil, ctx.Err()
+	}
+	renderer := NewRenderer(r)
+	defer renderer.ClearCache()
+	visitor := &compressionImages{ctx: ctx, dpi: dpi, sizes: make(map[string]image.Point)}
+	for index := 0; index < count; index++ {
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		page, err := r.PageContentByIndex(index)
+		if err != nil {
+			return nil, ctx.Err()
+		}
+		for _, ref := range page.Template {
+			if renderer.loadTemplate(ref.TemplateID) == nil {
+				return nil, ctx.Err()
+			}
+		}
+		if err := renderer.WalkPage(page, visitor); err != nil {
+			return nil, ctx.Err()
+		}
+	}
+	result := make(map[string]image.Point)
+	for _, img := range images {
+		name := strings.ToLower(cleanPackagePath(img.Location))
+		size := visitor.sizes[img.ID]
+		old := result[name]
+		result[name] = image.Pt(max(old.X, size.X), max(old.Y, size.Y))
+	}
+	return result, ctx.Err()
+}
+
+// DrawObject 收集图片的完整显示尺寸，不使用裁剪后的局部面积
+// 入参: object 图形对象, state 继承状态
+// 返回: error 取消或几何错误
+func (v *compressionImages) DrawObject(object *GraphicObject, state RenderState) error {
+	if err := v.ctx.Err(); err != nil {
+		return err
+	}
+	if object.Type != "ImageObject" {
+		return nil
+	}
+	img := object.ImageObject
+	box, err := ParseBox(img.Boundary)
+	if err != nil {
+		return err
+	}
+	local := NewMatrix(img.CTM)
+	if img.CTM == "" {
+		local = Matrix{a: box.W, d: box.H}
+	}
+	matrix, _ := renderObjectMatrix(img.Boundary, local, state)
+	size := compressionImageSize(math.Hypot(matrix.a, matrix.b), math.Hypot(matrix.c, matrix.d), v.dpi)
+	if size.X == 0 || size.Y == 0 {
+		return fmt.Errorf("invalid image placement")
+	}
+	old := v.sizes[img.ResourceID]
+	v.sizes[img.ResourceID] = image.Pt(max(old.X, size.X), max(old.Y, size.Y))
+	return nil
+}
+
+// DrawStamp 保留签章内容，不参与图片降采样
+// 入参: stamp 印章
+// 返回: error 始终为空
+func (v *compressionImages) DrawStamp(stamp Stamp) error { return nil }