feat(后端架构): 接入GoGPU渲染，支持后端切换

ofdgo_raster_image.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 ofdgo
+
+import (
+	"image"
+
+	"golang.org/x/image/draw"
+	"golang.org/x/image/math/f64"
+)
+
+// drawRasterImage 按页面变换采样图像，两后端共享相同的高质量图像插值
+// 入参: dst 目标图像, src 源图像, m 像素坐标变换
+func drawRasterImage(dst draw.Image, src image.Image, m RasterMatrix) {
+	draw.CatmullRom.Transform(dst, f64.Aff3{m[0], m[2], m[4], m[1], m[3], m[5]}, src, src.Bounds(), draw.Over, nil)
+}
+
+// PixelTransform 将页面毫米变换转换为像素变换，保留尺寸取整后的原点位置
+// 入参: m 局部到页面变换, height 目标像素高度
+// 返回: RasterMatrix 局部到像素变换
+func (p *RasterPage) PixelTransform(m RasterMatrix, height int) RasterMatrix {
+	scale := p.DPI / 25.4
+	for i := range m {
+		m[i] *= scale
+	}
+	m[5] += float64(height) - p.Height*scale
+	return m
+}