feat(媒体支持): 完善媒体播放与资源释放

ofdgo_pdf_halftone.go

@@ -0,0 +1,45 @@
+// 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 "github.com/xiaoqidun/pdfgo"
+
+// halftone 检查连续色调转换及不可忽略的传递函数，避免将打印网屏误用于屏幕显示
+// 入参: style 图形状态
+// 返回: error 严格模式或非恒等传递函数无法表达
+func (p *pdfImporter) halftone(style pdfgo.Style) error {
+	h := style.Halftone
+	if h == nil {
+		return nil
+	}
+	identity, err := h.IdentityTransfer(p.reader)
+	if err != nil {
+		return err
+	}
+	if !identity {
+		return &pdfgo.UnsupportedError{Feature: "halftone transfer function conversion"}
+	}
+	if p.warning == nil {
+		return &pdfgo.UnsupportedError{Feature: "device halftone conversion"}
+	}
+	if p.halftoneWarnings == nil {
+		p.halftoneWarnings = make(map[*pdfgo.Halftone]bool)
+	}
+	if !p.halftoneWarnings[h] {
+		p.halftoneWarnings[h] = true
+		p.warning(pdfgo.Diagnostic{Message: "PDF continuous-tone appearance retained; device halftone not transferred to OFD"})
+	}
+	return nil
+}