doodle/pkg/uix/canvas_zoom.go

package uix

import (
	"git.kirsle.net/apps/doodle/pkg/drawtool"
	"git.kirsle.net/go/render"
)

// Functions related to the Zoom Tool to magnify the size of the canvas.

/*
GetZoomMultiplier parses the .Zoom integer and returns a multiplier.

Examples:

	Zoom = 0: neutral (100% scale, 1x)
	Zoom = 1: 2x zoom
	Zoom = 2: 4x zoom
	Zoom = 3: 8x zoom
	Zoom = -1: 0.5x zoom
	Zoom = -2: 0.25x zoom
*/
func (w *Canvas) GetZoomMultiplier() float64 {
	// Get and bounds cap the zoom setting.
	if w.Zoom < -2 {
		w.Zoom = -2
	} else if w.Zoom > 3 {
		w.Zoom = 3
	}

	// Return the multipliers.
	switch w.Zoom {
	case -2:
		return 0.25
	case -1:
		return 0.5
	case 0:
		return 1
	case 1:
		return 1.5
	case 2:
		return 2
	case 3:
		return 2.5
	default:
		return 1
	}
}

/*
ZoomMultiply multiplies a width or height value by the Zoom Multiplier and
returns the modified integer.

Usage is like:

	// when building a render.Rect destination box.
	dest.W *= ZoomMultiply(dest.W)
	dest.H *= ZoomMultiply(dest.H)
*/
func (w *Canvas) ZoomMultiply(value int) int {
	return int(float64(value) * w.GetZoomMultiplier())
}

/*
ZoomDivide divides an integer by the zoom inversely.

The algo is: int(float64(value) * divider)

Where the divider is a map of:

	w.Zoom => divider
	-2 => 4
	-1 => 2
	0  => 1
	1  => 0.675*
	2  => 0.5
	3  => 0.404*

The 0.675 and 0.404 numbers I don't understand but were
discovered the hard way when the 1.5x and 2.5x zoom levels
were coming out jank. Expected to be 0.25 and 0.75.
*/
func (w *Canvas) ZoomDivide(value int) int {
	var divider float64
	switch w.Zoom {
	case -2:
		divider = 4
	case -1:
		divider = 2
	case 0:
		divider = 1
	case 1:
		divider = 0.675 // JANK
	case 2:
		divider = 0.5 // GOOD, 2x (200%) zoom in
	case 3:
		divider = 0.404 // JANK
	default:
		divider = 1
	}
	return int(float64(value) * divider)
}

/*
ZoomStroke adjusts a drawn stroke on the canvas to account for the zoom level.

Returns a copy Stroke value without changing the original.
*/
func (w *Canvas) ZoomStroke(stroke *drawtool.Stroke) *drawtool.Stroke {
	copy := &drawtool.Stroke{
		ID:             stroke.ID,
		Shape:          stroke.Shape,
		Color:          stroke.Color,
		Thickness:      stroke.Thickness,
		ExtraData:      stroke.ExtraData,
		PointA:         stroke.PointA,
		PointB:         stroke.PointB,
		Points:         stroke.Points,
		OriginalPoints: stroke.OriginalPoints,
	}

	// Multiply all coordinates in this stroke, which should be World
	// Coordinates in the level data, by the zoom multiplier.
	adjust := func(p render.Point) render.Point {
		p.X = w.ZoomDivide(p.X)
		p.Y = w.ZoomDivide(p.Y)
		return p
	}

	copy.PointA = adjust(copy.PointA)
	copy.PointB = adjust(copy.PointB)
	for i := range copy.Points {
		copy.Points[i] = adjust(copy.Points[i])
	}

	return copy
}