github.com/neohugo/neohugo@v0.123.8/resources/images/opacity.go (about)

     1  // Copyright 2024 The Hugo Authors. All rights reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  // http://www.apache.org/licenses/LICENSE-2.0
     7  //
     8  // Unless required by applicable law or agreed to in writing, software
     9  // distributed under the License is distributed on an "AS IS" BASIS,
    10  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    11  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package images
    15  
    16  import (
    17  	"image"
    18  	"image/color"
    19  	"image/draw"
    20  
    21  	"github.com/disintegration/gift"
    22  )
    23  
    24  var _ gift.Filter = (*opacityFilter)(nil)
    25  
    26  type opacityFilter struct {
    27  	opacity float32
    28  }
    29  
    30  func (f opacityFilter) Draw(dst draw.Image, src image.Image, options *gift.Options) {
    31  	// 0 is fully transparent and 255 is opaque.
    32  	alpha := uint8(f.opacity * 255)
    33  	mask := image.NewUniform(color.Alpha{alpha})
    34  	draw.DrawMask(dst, dst.Bounds(), src, image.Point{}, mask, image.Point{}, draw.Over)
    35  }
    36  
    37  func (f opacityFilter) Bounds(srcBounds image.Rectangle) image.Rectangle {
    38  	return image.Rect(0, 0, srcBounds.Dx(), srcBounds.Dy())
    39  }