imgproxy/processing/gravity.go

package processing

import (
	"github.com/imgproxy/imgproxy/v3/options"
	"github.com/imgproxy/imgproxy/v3/options/keys"
)

var gravityTypesRotationMap = map[int]map[GravityType]GravityType{
	90: {
		GravityNorth:     GravityWest,
		GravityEast:      GravityNorth,
		GravitySouth:     GravityEast,
		GravityWest:      GravitySouth,
		GravityNorthWest: GravitySouthWest,
		GravityNorthEast: GravityNorthWest,
		GravitySouthWest: GravitySouthEast,
		GravitySouthEast: GravityNorthEast,
	},
	180: {
		GravityNorth:     GravitySouth,
		GravityEast:      GravityWest,
		GravitySouth:     GravityNorth,
		GravityWest:      GravityEast,
		GravityNorthWest: GravitySouthEast,
		GravityNorthEast: GravitySouthWest,
		GravitySouthWest: GravityNorthEast,
		GravitySouthEast: GravityNorthWest,
	},
	270: {
		GravityNorth:     GravityEast,
		GravityEast:      GravitySouth,
		GravitySouth:     GravityWest,
		GravityWest:      GravityNorth,
		GravityNorthWest: GravityNorthEast,
		GravityNorthEast: GravitySouthEast,
		GravitySouthWest: GravityNorthWest,
		GravitySouthEast: GravitySouthWest,
	},
}

var gravityTypesFlipXMap = map[GravityType]GravityType{
	GravityEast:      GravityWest,
	GravityWest:      GravityEast,
	GravityNorthWest: GravityNorthEast,
	GravityNorthEast: GravityNorthWest,
	GravitySouthWest: GravitySouthEast,
	GravitySouthEast: GravitySouthWest,
}

var gravityTypesFlipYMap = map[GravityType]GravityType{
	GravityNorth:     GravitySouth,
	GravitySouth:     GravityNorth,
	GravityNorthWest: GravitySouthWest,
	GravityNorthEast: GravitySouthEast,
	GravitySouthWest: GravityNorthWest,
	GravitySouthEast: GravityNorthEast,
}

type GravityOptions struct {
	Type GravityType
	X, Y float64
}

// NewGravityOptions builds a new [GravityOptions] instance.
// It fills the [GravityOptions] struct with the options values under the given prefix.
// If the gravity type is not set in the options,
// it returns a [GravityOptions] with the provided default type.
func NewGravityOptions(o *options.Options, prefix string, defType GravityType) GravityOptions {
	gr := GravityOptions{
		Type: options.Get(o, prefix+keys.SuffixType, defType),
		X:    o.GetFloat(prefix+keys.SuffixXOffset, 0.0),
		Y:    o.GetFloat(prefix+keys.SuffixYOffset, 0.0),
	}

	return gr
}

// RotateAndFlip rotates and flips the gravity options so that they correspond
// to the image before rotation and flipping.
//
// By design, rotation and flipping are applied before cropping.
// But for performance reasons, we do cropping before rotation and flipping.
// So we need to adjust gravity options accordingly.
// As a result, cropping with the adjusted gravity options
// and then rotating/flipping the cropped image gives the same result
// as rotating/flipping the image first and then cropping
// with the original gravity options.
func (g *GravityOptions) RotateAndFlip(angle int, flipX, flipY bool) {
	angle %= 360

	if flipX {
		if gt, ok := gravityTypesFlipXMap[g.Type]; ok {
			g.Type = gt
		}

		switch g.Type {
		case GravityCenter, GravityNorth, GravitySouth:
			g.X = -g.X
		case GravityFocusPoint:
			g.X = 1.0 - g.X
		}
	}

	if flipY {
		if gt, ok := gravityTypesFlipYMap[g.Type]; ok {
			g.Type = gt
		}

		switch g.Type {
		case GravityCenter, GravityEast, GravityWest:
			g.Y = -g.Y
		case GravityFocusPoint:
			g.Y = 1.0 - g.Y
		}
	}

	if angle > 0 {
		if rotMap := gravityTypesRotationMap[angle]; rotMap != nil {
			if gt, ok := rotMap[g.Type]; ok {
				g.Type = gt
			}

			switch angle {
			case 90:
				switch g.Type {
				case GravityCenter, GravityEast, GravityWest:
					g.X, g.Y = g.Y, -g.X
				case GravityFocusPoint:
					g.X, g.Y = g.Y, 1.0-g.X
				default:
					g.X, g.Y = g.Y, g.X
				}
			case 180:
				switch g.Type {
				case GravityCenter:
					g.X, g.Y = -g.X, -g.Y
				case GravityNorth, GravitySouth:
					g.X = -g.X
				case GravityEast, GravityWest:
					g.Y = -g.Y
				case GravityFocusPoint:
					g.X, g.Y = 1.0-g.X, 1.0-g.Y
				}
			case 270:
				switch g.Type {
				case GravityCenter, GravityNorth, GravitySouth:
					g.X, g.Y = -g.Y, g.X
				case GravityFocusPoint:
					g.X, g.Y = 1.0-g.Y, g.X
				default:
					g.X, g.Y = g.Y, g.X
				}
			}
		}
	}
}