feat(强化兼容): 支持位图和优化字体渲染

ofdgo_image.go

@@ -0,0 +1,147 @@
+// 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 (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"image"
+	"image/color"
+)
+
+// decodeImageData 解码图片数据
+// 入参: data 图片数据
+// 返回: image.Image 图片对象, string 图片格式, error 错误信息
+func decodeImageData(data []byte) (image.Image, string, error) {
+	img, format, err := image.Decode(bytes.NewReader(data))
+	if err == nil {
+		return img, normalizeSealType(format), nil
+	}
+	if img, err := decodeBMPImage(data); err == nil {
+		return img, "bmp", nil
+	}
+	return nil, "", err
+}
+
+// decodeImageConfigData 解码图片尺寸
+// 入参: data 图片数据
+// 返回: image.Config 图片尺寸, string 图片格式, error 错误信息
+func decodeImageConfigData(data []byte) (image.Config, string, error) {
+	cfg, format, err := image.DecodeConfig(bytes.NewReader(data))
+	if err == nil {
+		return cfg, normalizeSealType(format), nil
+	}
+	if cfg, err := decodeBMPConfig(data); err == nil {
+		return cfg, "bmp", nil
+	}
+	return image.Config{}, "", err
+}
+
+// decodeBMPConfig 解码 BMP 尺寸
+// 入参: data 图片数据
+// 返回: image.Config 图片尺寸, error 错误信息
+func decodeBMPConfig(data []byte) (image.Config, error) {
+	offset, width, height, bpp, compression, err := parseBMPHeader(data)
+	if err != nil {
+		return image.Config{}, err
+	}
+	if offset <= 0 || width <= 0 || height == 0 || compression != 0 {
+		return image.Config{}, fmt.Errorf("unsupported bmp")
+	}
+	if bpp != 16 && bpp != 24 && bpp != 32 {
+		return image.Config{}, fmt.Errorf("unsupported bmp")
+	}
+	if height < 0 {
+		height = -height
+	}
+	return image.Config{ColorModel: color.NRGBAModel, Width: width, Height: height}, nil
+}
+
+// decodeBMPImage 解码 BMP 图片
+// 入参: data 图片数据
+// 返回: image.Image 图片对象, error 错误信息
+func decodeBMPImage(data []byte) (image.Image, error) {
+	offset, width, height, bpp, compression, err := parseBMPHeader(data)
+	if err != nil {
+		return nil, err
+	}
+	if compression != 0 {
+		return nil, fmt.Errorf("unsupported bmp compression")
+	}
+	topDown := height < 0
+	if topDown {
+		height = -height
+	}
+	if width <= 0 || height <= 0 {
+		return nil, fmt.Errorf("invalid bmp size")
+	}
+	rowStride := ((width*int(bpp) + 31) / 32) * 4
+	if offset+rowStride*height > len(data) {
+		return nil, fmt.Errorf("truncated bmp")
+	}
+	img := image.NewNRGBA(image.Rect(0, 0, width, height))
+	for y := 0; y < height; y++ {
+		srcY := y
+		if !topDown {
+			srcY = height - 1 - y
+		}
+		row := data[offset+srcY*rowStride:]
+		for x := 0; x < width; x++ {
+			switch bpp {
+			case 16:
+				v := binary.LittleEndian.Uint16(row[x*2:])
+				img.SetNRGBA(x, y, color.NRGBA{
+					R: uint8(((v >> 10) & 0x1F) * 255 / 31),
+					G: uint8(((v >> 5) & 0x1F) * 255 / 31),
+					B: uint8((v & 0x1F) * 255 / 31),
+					A: 255,
+				})
+			case 24:
+				p := x * 3
+				img.SetNRGBA(x, y, color.NRGBA{R: row[p+2], G: row[p+1], B: row[p], A: 255})
+			case 32:
+				p := x * 4
+				img.SetNRGBA(x, y, color.NRGBA{R: row[p+2], G: row[p+1], B: row[p], A: 255})
+			default:
+				return nil, fmt.Errorf("unsupported bmp")
+			}
+		}
+	}
+	return img, nil
+}
+
+// parseBMPHeader 解析 BMP 文件头
+// 入参: data 图片数据
+// 返回: int 像素偏移, int 宽度, int 高度, uint16 位数, uint32 压缩方式, error 错误信息
+func parseBMPHeader(data []byte) (int, int, int, uint16, uint32, error) {
+	if len(data) < 54 || string(data[:2]) != "BM" {
+		return 0, 0, 0, 0, 0, fmt.Errorf("not bmp")
+	}
+	offset := int(binary.LittleEndian.Uint32(data[10:14]))
+	dibSize := binary.LittleEndian.Uint32(data[14:18])
+	if dibSize < 40 {
+		return 0, 0, 0, 0, 0, fmt.Errorf("unsupported bmp")
+	}
+	width := int(int32(binary.LittleEndian.Uint32(data[18:22])))
+	height := int(int32(binary.LittleEndian.Uint32(data[22:26])))
+	planes := binary.LittleEndian.Uint16(data[26:28])
+	bpp := binary.LittleEndian.Uint16(data[28:30])
+	compression := binary.LittleEndian.Uint32(data[30:34])
+	if planes != 1 {
+		return 0, 0, 0, 0, 0, fmt.Errorf("invalid bmp")
+	}
+	return offset, width, height, bpp, compression, nil
+}