transform.go

package xtx

import (
	"image"
	"image/color"

	"golang.org/x/image/draw"
)

// Resize scales img to the given width and height using bilinear
// interpolation. For aspect-ratio-preserving variants,
// use ResizeToWidth or ResizeToHeight.
func Resize(img image.Image, width, height int) *image.RGBA {
	if width < 1 {
		width = 1
	}
	if height < 1 {
		height = 1
	}
	dst := image.NewRGBA(image.Rect(0, 0, width, height))
	draw.ApproxBiLinear.Scale(dst, dst.Bounds(), img, img.Bounds(), draw.Over, nil)
	return dst
}

// ResizeToWidth scales img so its width equals targetWidth, maintaining
// the original aspect ratio. Uses bilinear interpolation.
func ResizeToWidth(img image.Image, targetWidth int) *image.RGBA {
	bounds := img.Bounds()
	srcW, srcH := bounds.Dx(), bounds.Dy()
	if srcW == targetWidth {
		// Convert to RGBA if needed.
		dst := image.NewRGBA(bounds)
		draw.Draw(dst, bounds, img, bounds.Min, draw.Src)
		return dst
	}
	targetHeight := srcH * targetWidth / srcW
	return Resize(img, targetWidth, targetHeight)
}

// ResizeToHeight scales img so its height equals targetHeight, maintaining
// the original aspect ratio. Uses bilinear interpolation.
func ResizeToHeight(img image.Image, targetHeight int) *image.RGBA {
	bounds := img.Bounds()
	srcW, srcH := bounds.Dx(), bounds.Dy()
	if srcH == targetHeight {
		dst := image.NewRGBA(bounds)
		draw.Draw(dst, bounds, img, bounds.Min, draw.Src)
		return dst
	}
	targetWidth := srcW * targetHeight / srcH
	return Resize(img, targetWidth, targetHeight)
}

// RotateCW rotates an image 90° clockwise.
// A W×H image becomes H×W.
func RotateCW(img image.Image) *image.RGBA {
	bounds := img.Bounds()
	w, h := bounds.Dx(), bounds.Dy()
	dst := image.NewRGBA(image.Rect(0, 0, h, w))
	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
		for x := bounds.Min.X; x < bounds.Max.X; x++ {
			// Source (x,y) → destination (h-1-(y-minY), x-minX)
			dst.Set(h-1-(y-bounds.Min.Y), x-bounds.Min.X, img.At(x, y))
		}
	}
	return dst
}

// RotateCCW rotates an image 90° counter-clockwise.
// A W×H image becomes H×W.
func RotateCCW(img image.Image) *image.RGBA {
	bounds := img.Bounds()
	w, h := bounds.Dx(), bounds.Dy()
	dst := image.NewRGBA(image.Rect(0, 0, h, w))
	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
		for x := bounds.Min.X; x < bounds.Max.X; x++ {
			// Source (x,y) → destination (y-minY, w-1-(x-minX))
			dst.Set(y-bounds.Min.Y, w-1-(x-bounds.Min.X), img.At(x, y))
		}
	}
	return dst
}

// NewWhitePage creates a new RGBA image of the given dimensions filled with white.
func NewWhitePage(w, h int) *image.RGBA {
	page := image.NewRGBA(image.Rect(0, 0, w, h))
	draw.Draw(page, page.Bounds(), image.NewUniform(color.White), image.Point{}, draw.Src)
	return page
}