resize.go

package main

import (
	"image"

	"github.com/nfnt/resize"
	"github.com/qeesung/image2ascii/terminal"
)

// NewResizeHandler create a new resize handler
func NewResizeHandler() ResizeHandler {
	handler := &ImageResizeHandler{
		terminal: terminal.NewTerminalAccessor(),
	}

	initResizeResolver(handler)
	return handler
}

// initResizeResolver register the size resolvers
func initResizeResolver(handler *ImageResizeHandler) {
	sizeResolvers := make([]imageSizeResolver, 0, 5)
	// fixed height or width resolver
	sizeResolvers = append(sizeResolvers, imageSizeResolver{
		match: func(options *Options) bool {
			return options.FixedWidth != -1 || options.FixedHeight != -1
		},
		compute: func(sz image.Rectangle, options *Options, handler *ImageResizeHandler) (width, height int, err error) {
			height = sz.Max.Y
			width = sz.Max.X
			if options.FixedWidth != -1 {
				width = options.FixedWidth
			}

			if options.FixedHeight != -1 {
				height = options.FixedHeight
			}
			return
		},
	})
	// scaled by ratio
	sizeResolvers = append(sizeResolvers, imageSizeResolver{
		match: func(options *Options) bool {
			return options.Ratio != 1
		},
		compute: func(sz image.Rectangle, options *Options, handler *ImageResizeHandler) (width, height int, err error) {
			ratio := options.Ratio
			width = handler.ScaleWidthByRatio(float64(sz.Max.X), ratio)
			height = handler.ScaleHeightByRatio(float64(sz.Max.Y), ratio)
			return
		},
	})
	// scaled by stretched screen
	sizeResolvers = append(sizeResolvers, imageSizeResolver{
		match: func(options *Options) bool {
			return options.StretchedScreen
		},
		compute: func(sz image.Rectangle, options *Options, handler *ImageResizeHandler) (width, height int, err error) {
			return handler.ScreenSize()
		},
	})
	// scaled by fit the screen
	sizeResolvers = append(sizeResolvers, imageSizeResolver{
		match: func(options *Options) bool {
			return options.FitScreen
		},
		compute: func(sz image.Rectangle, options *Options, handler *ImageResizeHandler) (width, height int, err error) {
			return handler.CalcProportionalFittingScreenSize(sz)
		},
	})
	// default size
	sizeResolvers = append(sizeResolvers, imageSizeResolver{
		match: func(options *Options) bool {
			return true
		},
		compute: func(sz image.Rectangle, options *Options, handler *ImageResizeHandler) (width, height int, err error) {
			return sz.Max.X, sz.Max.Y, nil
		},
	})

	handler.imageSizeResolvers = sizeResolvers
}

// ResizeHandler define the operation to resize a image
type ResizeHandler interface {
	ScaleImage(image image.Image, options *Options) (newImage image.Image, err error)
}

// ImageResizeHandler implement the ResizeHandler interface and
// responsible for image resizing
type ImageResizeHandler struct {
	terminal           terminal.Terminal
	imageSizeResolvers []imageSizeResolver
}

// imageSizeResolver to resolve the image size from the options
type imageSizeResolver struct {
	match   func(options *Options) bool
	compute func(sz image.Rectangle, options *Options, handler *ImageResizeHandler) (width, height int, err error)
}

func (handler *ImageResizeHandler) ScreenSize() (width, height int, err error) {
	width, height, err = handler.terminal.ScreenSize()
	if err != nil {
		// return 157, 40, nil // default full screen size for mac os mock on container
		return 80, 24, nil // smaller terminal mocking
	}
	return width, height, nil
}

func (handler *ImageResizeHandler) CharWidth() (width float64) {
	width = handler.terminal.CharWidth()
	if width <= 0.01 {
		return 0.5 // default char width for mac os mock on container
	}
	return width
}

// ScaleImage resize the convert to expected size base on the convert options
func (handler *ImageResizeHandler) ScaleImage(image image.Image, options *Options) (newImage image.Image, err error) {
	sz := image.Bounds()
	newWidth, newHeight, err := handler.resolveSize(sz, options)
	if err != nil {
		return nil, err
	}

	newImage = resize.Resize(uint(newWidth), uint(newHeight), image, resize.Lanczos3)
	return newImage, nil
}

// resolveSize resolve the image size
func (handler *ImageResizeHandler) resolveSize(sz image.Rectangle, options *Options) (width, height int, err error) {
	for _, resolver := range handler.imageSizeResolvers {
		if resolver.match(options) {
			return resolver.compute(sz, options, handler)
		}
	}
	return sz.Max.X, sz.Max.Y, nil
}

// CalcProportionalFittingScreenSize proportional scale the image
// so that the terminal can just show the picture.
func (handler *ImageResizeHandler) CalcProportionalFittingScreenSize(sz image.Rectangle) (newWidth, newHeight int, err error) {
	screenWidth, screenHeight, err := handler.ScreenSize()
	if err != nil {
		return 0, 0, err
	}
	newWidth, newHeight = handler.CalcFitSize(
		float64(screenWidth),
		float64(screenHeight),
		float64(sz.Max.X),
		float64(sz.Max.Y))
	return
}

// CalcFitSizeRatio through the given length and width,
// the computation can match the optimal scaling ratio of the length and width.
// In other words, it is able to give a given size rectangle to contain pictures
// Either match the width first, then scale the length equally,
// or match the length first, then scale the height equally.
// More detail please check the example
func (handler *ImageResizeHandler) CalcFitSizeRatio(width, height, imageWidth, imageHeight float64) (ratio float64) {
	ratio = 1.0
	// try to fit the height
	ratio = height / imageHeight
	scaledWidth := imageWidth * ratio / handler.CharWidth()
	if scaledWidth < width {
		return ratio / handler.CharWidth()
	}

	// try to fit the width
	ratio = width / imageWidth
	return ratio
}

// CalcFitSize through the given length and width ,
// Calculation is able to match the length and width of
// the specified size, and is proportional scaling.
func (handler *ImageResizeHandler) CalcFitSize(width, height, toBeFitWidth, toBeFitHeight float64) (fitWidth, fitHeight int) {
	ratio := handler.CalcFitSizeRatio(width, height, toBeFitWidth, toBeFitHeight)
	fitWidth = handler.ScaleWidthByRatio(toBeFitWidth, ratio)
	fitHeight = handler.ScaleHeightByRatio(toBeFitHeight, ratio)
	return
}

// ScaleWidthByRatio scaled the width by ratio
func (handler *ImageResizeHandler) ScaleWidthByRatio(width float64, ratio float64) int {
	return int(width * ratio)
}

// ScaleHeightByRatio scaled the height by ratio
func (handler *ImageResizeHandler) ScaleHeightByRatio(height float64, ratio float64) int {
	return int(height * ratio * handler.CharWidth())
}