feat(后端结构): 完善多后端解耦，清理遗留代码

ofdgo_renderer_state_canvas.go

@@ -0,0 +1,58 @@
+// 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 (
+	"image"
+
+	"github.com/tdewolff/canvas"
+)
+
+// canvasBackendState 保存Canvas字体、字形和编码图片适配缓存
+type canvasBackendState struct {
+	images             map[*EncodedImage]image.Image
+	fontFamily         *canvas.FontFamily
+	defaultFontLoaded  bool
+	fontMap            map[string]*canvas.FontFamily
+	fontCache          map[fontCacheKey]*canvas.FontFamily
+	svgFontCache       map[*canvas.Font]SVGFont
+	fontSourceCache    map[string][]fontSource
+	fontSourceUsed     map[string]fontSource
+	fontDirCandidates  map[string][]fontFileCandidate
+	fontFSCandidates   map[int][]fontFileCandidate
+	textGlyphPathCache map[textGlyphPathCacheKey]textGlyphPathCacheValue
+}
+
+// canvasState 获取当前渲染器的Canvas私有缓存，按需创建且不向其他后端暴露
+// 返回: *canvasBackendState Canvas缓存
+func (r *Renderer) canvasState() *canvasBackendState {
+	key := CanvasBackend{}
+	if state, ok := r.backendStates[key]; ok {
+		return state.(*canvasBackendState)
+	}
+	state := &canvasBackendState{
+		images:             make(map[*EncodedImage]image.Image),
+		fontMap:            make(map[string]*canvas.FontFamily),
+		fontCache:          make(map[fontCacheKey]*canvas.FontFamily),
+		svgFontCache:       make(map[*canvas.Font]SVGFont),
+		fontSourceCache:    make(map[string][]fontSource),
+		fontSourceUsed:     make(map[string]fontSource),
+		fontDirCandidates:  make(map[string][]fontFileCandidate),
+		fontFSCandidates:   make(map[int][]fontFileCandidate),
+		textGlyphPathCache: make(map[textGlyphPathCacheKey]textGlyphPathCacheValue),
+	}
+	r.backendStates[key] = state
+	return state
+}