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line.go
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line.go
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package render
import (
"image"
"image/color"
"math"
"github.com/oakmound/oak/v3/alg/range/colorrange"
)
// Todo:
// Our current concept of thickness expands out in both directions,
// so it's impossible to draw a even-pixel thick line. This is probably
// okay for an easy syntax like this but we might want to add in a
// "Line constructor" type object like our ray-casters
// so this behavior can be customized, i.e.-- if you take thickness as
// pixel thickness, do you expand out left or right, or center, and how
// are ties broken, etc. That would also help prevent the number of
// different functions for line-drawing from continually increasing.
// NewLine returns a line from x1,y1 to x2,y2 with the given color
func NewLine(x1, y1, x2, y2 float64, c color.Color) *Sprite {
return NewThickLine(x1, y1, x2, y2, c, 0)
}
// NewThickLine returns a Line that has some value of thickness
func NewThickLine(x1, y1, x2, y2 float64, c color.Color, thickness int) *Sprite {
return NewColoredLine(x1, y1, x2, y2, IdentityColorer(c), thickness)
}
// NewGradientLine returns a Line that has some value of thickness along with a start and end color
func NewGradientLine(x1, y1, x2, y2 float64, c1, c2 color.Color, thickness int) *Sprite {
colorer := colorrange.NewLinear(c1, c2).Percentile
return NewColoredLine(x1, y1, x2, y2, colorer, thickness)
}
// NewColoredLine returns a line with a custom function for how each pixel in that line should be colored.
func NewColoredLine(x1, y1, x2, y2 float64, colorer Colorer, thickness int) *Sprite {
var rgba *image.RGBA
// We subtract the minimum from each side here
// to normalize the new line segment toward the origin
minX := math.Min(x1, x2)
minY := math.Min(y1, y2)
rgba = drawLineBetween(int(x1-minX), int(y1-minY), int(x2-minX), int(y2-minY), colorer, thickness)
return NewSprite(minX-float64(thickness), minY-float64(thickness), rgba)
}
// DrawLine draws a line onto an image rgba from one point to another
func DrawLine(rgba *image.RGBA, x1, y1, x2, y2 int, c color.Color) {
DrawThickLine(rgba, x1, y1, x2, y2, c, 0)
}
// DrawThickLine acts like DrawlineOnto, but takes in thickness of the given line
func DrawThickLine(rgba *image.RGBA, x1, y1, x2, y2 int, c color.Color, thickness int) {
DrawLineColored(rgba, x1, y1, x2, y2, thickness, IdentityColorer(c))
}
//DrawGradientLine acts like DrawThickLine but also applies a gradient to the line
func DrawGradientLine(rgba *image.RGBA, x1, y1, x2, y2 int, c1, c2 color.Color, thickness int) {
colorer := colorrange.NewLinear(c1, c2).Percentile
DrawLineColored(rgba, x1, y1, x2, y2, thickness, colorer)
}
// DrawLineColored acts like DrawThickLine, but takes in a custom colorer function for how it draws its line.
func DrawLineColored(rgba *image.RGBA, x1, y1, x2, y2, thickness int, colorer Colorer) {
xDelta := math.Abs(float64(x2 - x1))
yDelta := math.Abs(float64(y2 - y1))
xSlope := -1
x3 := x1
if x2 < x1 {
xSlope = 1
x3 = x2
}
ySlope := -1
y3 := y1
if y2 < y1 {
ySlope = 1
y3 = y2
}
w := int(xDelta)
h := int(yDelta)
progress := func(x, y, w, h int) float64 {
hprg := HorizontalProgress(x, y, w, h)
vprg := VerticalProgress(x, y, w, h)
if ySlope == -1 {
vprg = 1 - vprg
}
if xSlope == -1 {
hprg = 1 - hprg
}
return (hprg + vprg) / 2
}
err := xDelta - yDelta
var err2 float64
for i := 0; true; i++ {
for xm := x2 - thickness; xm <= (x2 + thickness); xm++ {
for ym := y2 - thickness; ym <= (y2 + thickness); ym++ {
p := progress(xm-x3, ym-y3, w, h)
rgba.Set(xm, ym, colorer(p))
}
}
if x2 == x1 && y2 == y1 {
break
}
err2 = 2 * err
if err2 > -1*yDelta {
err -= yDelta
x2 += xSlope
}
if err2 < xDelta {
err += xDelta
y2 += ySlope
}
}
}
func drawLineBetween(x1, y1, x2, y2 int, colorer Colorer, thickness int) *image.RGBA {
// Bresenham's line-drawing algorithm from wikipedia
xDelta := math.Abs(float64(x2 - x1))
yDelta := math.Abs(float64(y2 - y1))
if xDelta == 0 && yDelta == 0 {
width := 1 + 2*thickness
rect := image.Rect(0, 0, width, width)
rgba := image.NewRGBA(rect)
for xm := 0; xm < width; xm++ {
for ym := 0; ym < width; ym++ {
rgba.Set(xm, ym, colorer(1.0))
}
}
return rgba
} else if xDelta == 0 {
width := 1 + 2*thickness
height := int(math.Floor(yDelta)) + 2*thickness
rect := image.Rect(0, 0, width, height)
rgba := image.NewRGBA(rect)
for xm := 0; xm < width; xm++ {
for ym := 0; ym < height; ym++ {
rgba.Set(xm, ym, colorer(float64(ym)/float64(height)))
}
}
return rgba
}
// Todo: document why we add one here
// It has something to do with zero-height rgbas, but is always useful
h := int(yDelta) + 1
rect := image.Rect(0, 0, int(xDelta)+2*thickness, h+2*thickness)
rgba := image.NewRGBA(rect)
x2 += thickness
y2 += thickness
x1 += thickness
y1 += thickness
DrawLineColored(rgba, x1, y1, x2, y2, thickness, colorer)
return rgba
}