mirror of
https://github.com/xiaoqidun/ofdgo.git
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110 lines
3.9 KiB
Go
110 lines
3.9 KiB
Go
// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package image
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import (
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"context"
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"image"
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"image/color"
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)
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// maskedTIFFImage 将独立透明蒙版叠加到主图，复用两个目录的只读像素
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type maskedTIFFImage struct {
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source, mask image.Image
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bounds image.Rectangle
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}
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// DecodeTIFF 解码主图及透明蒙版，保留颜色精度与高分辨率蒙版
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// 入参: ctx 取消上下文，可为nil, data TIFF编码, layout 主图布局
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// 返回: image.Image 图像, error 解码或取消错误
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func DecodeTIFF(ctx context.Context, data []byte, layout TIFFLayout) (image.Image, error) {
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source, err := decodeTIFFPixels(ctx, data, layout)
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if err != nil || layout.Transparency == nil {
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return source, err
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}
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mask, err := decodeTIFFPixels(ctx, data, *layout.Transparency)
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if err != nil {
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return nil, err
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}
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return &maskedTIFFImage{source: source, mask: mask, bounds: image.Rectangle{Max: layout.DisplaySize()}}, nil
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}
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// Bounds 返回主图和蒙版共同覆盖的像素区域
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// 返回: image.Rectangle 显示区域
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func (s *maskedTIFFImage) Bounds() image.Rectangle { return s.bounds }
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// ColorModel 返回保留原图采样精度的非预乘颜色模型
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// 返回: color.Model 颜色模型
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func (s *maskedTIFFImage) ColorModel() color.Model { return color.NRGBA64Model }
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// samplePoint 将显示坐标映射到主图或蒙版的像素中心
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// 入参: bounds 采样图像范围, x 横坐标, y 纵坐标
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// 返回: image.Point 采样坐标
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func (s *maskedTIFFImage) samplePoint(bounds image.Rectangle, x, y int) image.Point {
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size := s.bounds.Size()
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x, y = x-s.bounds.Min.X, y-s.bounds.Min.Y
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if bounds.Size() == size {
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return bounds.Min.Add(image.Pt(x, y))
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}
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return image.Pt(
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bounds.Min.X+int((uint64(x)*uint64(bounds.Dx())+uint64(bounds.Dx()/2))/uint64(size.X)),
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bounds.Min.Y+int((uint64(y)*uint64(bounds.Dy())+uint64(bounds.Dy()/2))/uint64(size.Y)),
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)
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}
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// alphaAt 读取蒙版与主图透明度，不解算主图颜色
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// 入参: x 横坐标, y 纵坐标
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// 返回: uint32 十六位透明度
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func (s *maskedTIFFImage) alphaAt(x, y int) uint32 {
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if !image.Pt(x, y).In(s.bounds) {
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return 0
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}
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mask := s.samplePoint(s.mask.Bounds(), x, y)
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if NRGBA64At(s.mask, mask.X, mask.Y).R == 0 {
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return 0
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}
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source := s.samplePoint(s.source.Bounds(), x, y)
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return AlphaAt(s.source, source.X, source.Y)
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}
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// NRGBA64At 按像素中心读取主图及蒙版，零位隐藏原图并保留隐藏颜色
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// 入参: x 横坐标, y 纵坐标
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// 返回: color.NRGBA64 非预乘十六位颜色
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func (s *maskedTIFFImage) NRGBA64At(x, y int) color.NRGBA64 {
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if !image.Pt(x, y).In(s.bounds) {
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return color.NRGBA64{}
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}
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source := s.samplePoint(s.source.Bounds(), x, y)
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pixel := NRGBA64At(s.source, source.X, source.Y)
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mask := s.samplePoint(s.mask.Bounds(), x, y)
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if NRGBA64At(s.mask, mask.X, mask.Y).R == 0 {
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pixel.A = 0
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}
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return pixel
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}
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// At 返回非预乘颜色，区域外透明
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// 入参: x 横坐标, y 纵坐标
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// 返回: color.Color 像素颜色
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func (s *maskedTIFFImage) At(x, y int) color.Color { return s.NRGBA64At(x, y) }
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// RGBA64At 返回预乘十六位颜色，供采样器直接读取
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// 入参: x 横坐标, y 纵坐标
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// 返回: color.RGBA64 预乘颜色
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func (s *maskedTIFFImage) RGBA64At(x, y int) color.RGBA64 {
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r, g, b, a := s.NRGBA64At(x, y).RGBA()
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return color.RGBA64{R: uint16(r), G: uint16(g), B: uint16(b), A: uint16(a)}
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}
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