upstream-mattermost/server/channels/app/imaging/utils.go

// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
// See LICENSE.txt for license information.

package imaging

import (
	"image"
	"image/color"

	"github.com/boxes-ltd/imaging"
)

type rawImg interface {
	Set(x, y int, c color.Color)
	Opaque() bool
}

func isFullyTransparent(c color.Color) bool {
	// TODO: This can be optimized by checking the color type and
	// only extract the needed alpha value.
	_, _, _, a := c.RGBA()
	return a == 0
}

// FillImageTransparency fills in-place all the fully transparent pixels of the
// input image with the given color.
func FillImageTransparency(img image.Image, c color.Color) {
	var i rawImg

	bounds := img.Bounds()

	fillFunc := func() {
		for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				if isFullyTransparent(img.At(x, y)) {
					i.Set(x, y, c)
				}
			}
		}
	}

	switch raw := img.(type) {
	case *image.Alpha:
		i = raw
	case *image.Alpha16:
		i = raw
	case *image.Gray:
		i = raw
	case *image.Gray16:
		i = raw
	case *image.NRGBA:
		i = raw
		col := color.NRGBAModel.Convert(c).(color.NRGBA)
		fillFunc = func() {
			for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
				for x := bounds.Min.X; x < bounds.Max.X; x++ {
					i := raw.PixOffset(x, y)
					if raw.Pix[i+3] == 0x00 {
						raw.Pix[i] = col.R
						raw.Pix[i+1] = col.G
						raw.Pix[i+2] = col.B
						raw.Pix[i+3] = col.A
					}
				}
			}
		}
	case *image.NRGBA64:
		i = raw
		col := color.NRGBA64Model.Convert(c).(color.NRGBA64)
		fillFunc = func() {
			for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
				for x := bounds.Min.X; x < bounds.Max.X; x++ {
					i := raw.PixOffset(x, y)
					a := uint16(raw.Pix[i+6])<<8 | uint16(raw.Pix[i+7])
					if a == 0 {
						raw.Pix[i] = uint8(col.R >> 8)
						raw.Pix[i+1] = uint8(col.R)
						raw.Pix[i+2] = uint8(col.G >> 8)
						raw.Pix[i+3] = uint8(col.G)
						raw.Pix[i+4] = uint8(col.B >> 8)
						raw.Pix[i+5] = uint8(col.B)
						raw.Pix[i+6] = uint8(col.A >> 8)
						raw.Pix[i+7] = uint8(col.A)
					}
				}
			}
		}
	case *image.Paletted:
		i = raw
		fillFunc = func() {
			for i := range raw.Palette {
				if isFullyTransparent(raw.Palette[i]) {
					raw.Palette[i] = c
				}
			}
		}
	case *image.RGBA:
		i = raw
		col := color.RGBAModel.Convert(c).(color.RGBA)
		fillFunc = func() {
			for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
				for x := bounds.Min.X; x < bounds.Max.X; x++ {
					i := raw.PixOffset(x, y)
					if raw.Pix[i+3] == 0x00 {
						raw.Pix[i] = col.R
						raw.Pix[i+1] = col.G
						raw.Pix[i+2] = col.B
						raw.Pix[i+3] = col.A
					}
				}
			}
		}
	case *image.RGBA64:
		i = raw
		col := color.RGBA64Model.Convert(c).(color.RGBA64)
		fillFunc = func() {
			for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
				for x := bounds.Min.X; x < bounds.Max.X; x++ {
					i := raw.PixOffset(x, y)
					a := uint16(raw.Pix[i+6])<<8 | uint16(raw.Pix[i+7])
					if a == 0 {
						raw.Pix[i] = uint8(col.R >> 8)
						raw.Pix[i+1] = uint8(col.R)
						raw.Pix[i+2] = uint8(col.G >> 8)
						raw.Pix[i+3] = uint8(col.G)
						raw.Pix[i+4] = uint8(col.B >> 8)
						raw.Pix[i+5] = uint8(col.B)
						raw.Pix[i+6] = uint8(col.A >> 8)
						raw.Pix[i+7] = uint8(col.A)
					}
				}
			}
		}
	default:
		return
	}

	if !i.Opaque() {
		fillFunc()
	}
}

// FillCenter creates an image with the specified dimensions and fills it with
// the centered and scaled source image.
func FillCenter(img image.Image, w, h int) *image.NRGBA {
	return imaging.Fill(img, w, h, imaging.Center, imaging.Lanczos)
}

// Fit scales down the image to fit within the specified maximum dimensions,
// preserving the aspect ratio.
func Fit(img image.Image, maxW, maxH int) *image.NRGBA {
	return imaging.Fit(img, maxW, maxH, imaging.Lanczos)
}