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# art
Art is a simple 2D software drawing library used by Tomo.

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// Package artutil provides utility functions for working with art's interfaces.
package artutil
import "art"
import "image"
import "art/shatter"
import "image/color"
// Fill fills the destination canvas with the given pattern.
func Fill (destination art.Canvas, source art.Pattern) (updated image.Rectangle) {
source.Draw(destination, destination.Bounds())
return destination.Bounds()
}
// DrawClip lets you draw several subsets of a pattern at once.
func DrawClip (
destination art.Canvas,
source art.Pattern,
bounds image.Rectangle,
subsets ...image.Rectangle,
) (
updatedRegion image.Rectangle,
) {
for _, subset := range subsets {
source.Draw(art.Cut(destination, subset), bounds)
updatedRegion = updatedRegion.Union(subset)
}
return
}
// DrawShatter is like an inverse of DrawClip, drawing nothing in the areas
// specified by "rocks".
func DrawShatter (
destination art.Canvas,
source art.Pattern,
bounds image.Rectangle,
rocks ...image.Rectangle,
) (
updatedRegion image.Rectangle,
) {
tiles := shatter.Shatter(bounds, rocks...)
return DrawClip(destination, source, bounds, tiles...)
}
// AllocateSample returns a new canvas containing the result of a pattern. The
// resulting canvas can be sourced from shape drawing functions. I beg of you
// please do not call this every time you need to draw a shape with a pattern on
// it because that is horrible and cruel to the computer.
func AllocateSample (source art.Pattern, width, height int) art.Canvas {
allocated := art.NewBasicCanvas(width, height)
Fill(allocated, source)
return allocated
}
// Hex creates a color.RGBA value from an RGBA integer value.
func Hex (color uint32) (c color.RGBA) {
c.A = uint8(color)
c.B = uint8(color >> 8)
c.G = uint8(color >> 16)
c.R = uint8(color >> 24)
return
}

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package art
import "image"
import "image/draw"
import "image/color"
// Image represents an immutable canvas.
type Image interface {
image.Image
RGBAAt (x, y int) color.RGBA
}
// Canvas is like draw.Image but is also able to return a raw pixel buffer for
// more efficient drawing. This interface can be easily satisfied using a
// BasicCanvas struct.
type Canvas interface {
draw.Image
Buffer () (data []color.RGBA, stride int)
}
// BasicCanvas is a general purpose implementation of tomo.Canvas.
type BasicCanvas struct {
pix []color.RGBA
stride int
rect image.Rectangle
}
// NewBasicCanvas creates a new basic canvas with the specified width and
// height, allocating a buffer for it.
func NewBasicCanvas (width, height int) (canvas BasicCanvas) {
canvas.pix = make([]color.RGBA, height * width)
canvas.stride = width
canvas.rect = image.Rect(0, 0, width, height)
return
}
// FromImage creates a new BasicCanvas from an image.Image.
func FromImage (img image.Image) (canvas BasicCanvas) {
bounds := img.Bounds()
canvas = NewBasicCanvas(bounds.Dx(), bounds.Dy())
point := image.Point { }
for point.Y = bounds.Min.Y; point.Y < bounds.Max.Y; point.Y ++ {
for point.X = bounds.Min.X; point.X < bounds.Max.X; point.X ++ {
canvasPoint := point.Sub(bounds.Min)
canvas.Set (
canvasPoint.X, canvasPoint.Y,
img.At(point.X, point.Y))
}}
return
}
// you know what it do
func (canvas BasicCanvas) Bounds () (bounds image.Rectangle) {
return canvas.rect
}
// you know what it do
func (canvas BasicCanvas) At (x, y int) (color.Color) {
if !image.Pt(x, y).In(canvas.rect) { return nil }
return canvas.pix[x + y * canvas.stride]
}
// you know what it do
func (canvas BasicCanvas) ColorModel () (model color.Model) {
return color.RGBAModel
}
// you know what it do
func (canvas BasicCanvas) Set (x, y int, c color.Color) {
if !image.Pt(x, y).In(canvas.rect) { return }
r, g, b, a := c.RGBA()
canvas.pix[x + y * canvas.stride] = color.RGBA {
R: uint8(r >> 8),
G: uint8(g >> 8),
B: uint8(b >> 8),
A: uint8(a >> 8),
}
}
// you know what it do
func (canvas BasicCanvas) Buffer () (data []color.RGBA, stride int) {
return canvas.pix, canvas.stride
}
// Reallocate efficiently reallocates the canvas. The data within will be
// garbage. This method will do nothing if this is a cut image.
func (canvas *BasicCanvas) Reallocate (width, height int) {
if canvas.rect.Min != (image.Point { }) { return }
previousLen := len(canvas.pix)
newLen := width * height
bigger := newLen > previousLen
smaller := newLen < previousLen / 2
if bigger || smaller {
canvas.pix = make (
[]color.RGBA,
((height * width) / 4096) * 4096 + 4096)
}
canvas.stride = width
canvas.rect = image.Rect(0, 0, width, height)
}
// Cut returns a sub-canvas of a given canvas.
func Cut (canvas Canvas, bounds image.Rectangle) (reduced BasicCanvas) {
// println(canvas.Bounds().String(), bounds.String())
bounds = bounds.Intersect(canvas.Bounds())
if bounds.Empty() { return }
reduced.rect = bounds
reduced.pix, reduced.stride = canvas.Buffer()
return
}

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// Package art provides a simple 2D drawing library.
package art

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module art
go 1.20

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icon.go Normal file
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package art
import "image"
import "image/color"
type Icon interface {
// Draw draws the icon to the destination canvas at the specified point,
// using the specified color (if the icon is monochrome).
Draw (destination Canvas, color color.RGBA, at image.Point)
// Bounds returns the bounds of the icon.
Bounds () image.Rectangle
}

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inset.go Normal file
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package art
import "image"
// Side represents one side of a rectangle.
type Side int; const (
SideTop Side = iota
SideRight
SideBottom
SideLeft
)
// Inset represents an inset amount for all four sides of a rectangle. The top
// side is at index zero, the right at index one, the bottom at index two, and
// the left at index three. These values may be negative.
type Inset [4]int
// I allows you to create an inset in a CSS-ish way:
//
// - One argument: all sides are set to this value
// - Two arguments: the top and bottom sides are set to the first value, and
// the left and right sides are set to the second value.
// - Three arguments: the top side is set by the first value, the left and
// right sides are set by the second vaue, and the bottom side is set by the
// third value.
// - Four arguments: each value corresponds to a side.
//
// This function will panic if an argument count that isn't one of these is
// given.
func I (sides ...int) Inset {
switch len(sides) {
case 1: return Inset { sides[0], sides[0], sides[0], sides[0] }
case 2: return Inset { sides[0], sides[1], sides[0], sides[1] }
case 3: return Inset { sides[0], sides[1], sides[2], sides[1] }
case 4: return Inset { sides[0], sides[1], sides[2], sides[3] }
default: panic("I: illegal argument count.")
}
}
// Apply returns the given rectangle, shrunk on all four sides by the given
// inset. If a measurment of the inset is negative, that side will instead be
// expanded outward. If the rectangle's dimensions cannot be reduced any
// further, an empty rectangle near its center will be returned.
func (inset Inset) Apply (bigger image.Rectangle) (smaller image.Rectangle) {
smaller = bigger
if smaller.Dx() < inset[3] + inset[1] {
smaller.Min.X = (smaller.Min.X + smaller.Max.X) / 2
smaller.Max.X = smaller.Min.X
} else {
smaller.Min.X += inset[3]
smaller.Max.X -= inset[1]
}
if smaller.Dy() < inset[0] + inset[2] {
smaller.Min.Y = (smaller.Min.Y + smaller.Max.Y) / 2
smaller.Max.Y = smaller.Min.Y
} else {
smaller.Min.Y += inset[0]
smaller.Max.Y -= inset[2]
}
return
}
// Inverse returns a negated version of the inset.
func (inset Inset) Inverse () (prime Inset) {
return Inset {
inset[0] * -1,
inset[1] * -1,
inset[2] * -1,
inset[3] * -1,
}
}
// Horizontal returns the sum of SideRight and SideLeft.
func (inset Inset) Horizontal () int {
return inset[SideRight] + inset[SideLeft]
}
// Vertical returns the sum of SideTop and SideBottom.
func (inset Inset) Vertical () int {
return inset[SideTop] + inset[SideBottom]
}

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package art
import "image"
// Pattern is capable of drawing to a canvas within the bounds of a given
// clipping rectangle.
type Pattern interface {
// Draw draws the pattern onto the destination canvas, using the
// specified bounds. The given bounds can be smaller or larger than the
// bounds of the destination canvas. The destination canvas can be cut
// using canvas.Cut() to draw only a specific subset of a pattern.
Draw (destination Canvas, bounds image.Rectangle)
}

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package patterns
import "art"
import "image"
// Border is a pattern that behaves similarly to border-image in CSS. It divides
// a source canvas into nine sections...
//
// Inset[1]
// ┌──┴──┐
// ┌─┌─────┬─────┬─────┐
// Inset[0]─┤ │ 0 │ 1 │ 2 │
// └─├─────┼─────┼─────┤
// │ 3 │ 4 │ 5 │
// ├─────┼─────┼─────┤─┐
// │ 6 │ 7 │ 8 │ ├─Inset[2]
// └─────┴─────┴─────┘─┘
// └──┬──┘
// Inset[3]
//
// ... Where the bounds of section 4 are defined as the application of the
// pattern's inset to the canvas's bounds. The bounds of the other eight
// sections are automatically sized around it.
//
// When drawn to a destination canvas, the bounds of sections 1, 3, 4, 5, and 7
// are expanded or contracted to fit the given drawing bounds. All sections are
// rendered as if they are Texture patterns, meaning these flexible sections
// will repeat to fill in any empty space.
//
// This pattern can be used to make a static image texture into something that
// responds well to being resized.
type Border struct {
art.Canvas
art.Inset
}
// Draw draws the border pattern onto the destination canvas within the given
// bounds.
func (pattern Border) Draw (destination art.Canvas, bounds image.Rectangle) {
drawBounds := bounds.Canon().Intersect(destination.Bounds())
if drawBounds.Empty() { return }
srcSections := nonasect(pattern.Bounds(), pattern.Inset)
srcTextures := [9]Texture { }
for index, section := range srcSections {
srcTextures[index].Canvas = art.Cut(pattern, section)
}
dstSections := nonasect(bounds, pattern.Inset)
for index, section := range dstSections {
srcTextures[index].Draw(destination, section)
}
}
func nonasect (bounds image.Rectangle, inset art.Inset) [9]image.Rectangle {
center := inset.Apply(bounds)
return [9]image.Rectangle {
// top
image.Rectangle {
bounds.Min,
center.Min },
image.Rect (
center.Min.X, bounds.Min.Y,
center.Max.X, center.Min.Y),
image.Rect (
center.Max.X, bounds.Min.Y,
bounds.Max.X, center.Min.Y),
// center
image.Rect (
bounds.Min.X, center.Min.Y,
center.Min.X, center.Max.Y),
center,
image.Rect (
center.Max.X, center.Min.Y,
bounds.Max.X, center.Max.Y),
// bottom
image.Rect (
bounds.Min.X, center.Max.Y,
center.Min.X, bounds.Max.Y),
image.Rect (
center.Min.X, center.Max.Y,
center.Max.X, bounds.Max.Y),
image.Rect (
center.Max.X, center.Max.Y,
bounds.Max.X, bounds.Max.Y),
}
}

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// Package patterns provides a basic set of types that satisfy the Pattern
// interface.
package patterns

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package patterns
import "art"
import "image"
// Texture is a pattern that tiles the content of a canvas both horizontally and
// vertically.
type Texture struct {
art.Canvas
}
// Draw tiles the pattern's canvas within the given bounds. The minimum
// point of the pattern's canvas will be lined up with the minimum point of the
// bounding rectangle.
func (pattern Texture) Draw (destination art.Canvas, bounds image.Rectangle) {
dstBounds := bounds.Canon().Intersect(destination.Bounds())
if dstBounds.Empty() { return }
dstData, dstStride := destination.Buffer()
srcData, srcStride := pattern.Buffer()
srcBounds := pattern.Bounds()
// offset is a vector that is added to points in destination space to
// convert them to points in source space
offset := srcBounds.Min.Sub(bounds.Min)
// calculate the starting position in source space
srcPoint := dstBounds.Min.Add(offset)
srcPoint.X = wrap(srcPoint.X, srcBounds.Min.X, srcBounds.Max.X)
srcPoint.Y = wrap(srcPoint.Y, srcBounds.Min.Y, srcBounds.Max.Y)
srcStartPoint := srcPoint
// for each row
dstPoint := image.Point { }
for dstPoint.Y = dstBounds.Min.Y; dstPoint.Y < dstBounds.Max.Y; dstPoint.Y ++ {
srcPoint.X = srcStartPoint.X
dstPoint.X = dstBounds.Min.X
dstYComponent := dstPoint.Y * dstStride
srcYComponent := srcPoint.Y * srcStride
// for each pixel in the row
for {
// draw pixel
dstIndex := dstYComponent + dstPoint.X
srcIndex := srcYComponent + srcPoint.X
dstData[dstIndex] = srcData[srcIndex]
// increment X in source space. wrap to start if out of
// bounds.
srcPoint.X ++
if srcPoint.X >= srcBounds.Max.X {
srcPoint.X = srcBounds.Min.X
}
// increment X in destination space. stop drawing this
// row if out of bounds.
dstPoint.X ++
if dstPoint.X >= dstBounds.Max.X {
break
}
}
// increment row in source space. wrap to start if out of
// bounds.
srcPoint.Y ++
if srcPoint.Y >= srcBounds.Max.Y {
srcPoint.Y = srcBounds.Min.Y
}
}
}
func wrap (value, min, max int) int {
difference := max - min
value = (value - min) % difference
if value < 0 { value += difference }
return value + min
}

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package patterns
import "art"
import "image"
import "art/shapes"
import "art/artutil"
import "image/color"
// Uniform is a pattern that draws a solid color.
type Uniform color.RGBA
// Draw fills the bounding rectangle with the pattern's color.
func (pattern Uniform) Draw (destination art.Canvas, bounds image.Rectangle) {
shapes.FillColorRectangle(destination, color.RGBA(pattern), bounds)
}
// Uhex creates a new Uniform pattern from an RGBA integer value.
func Uhex (color uint32) (uniform Uniform) {
return Uniform(artutil.Hex(color))
}

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// Package shapes provides some basic shape drawing routines.
//
// A word about using patterns with shape routines:
//
// Most drawing routines have a version that samples from other canvases, and a
// version that samples from a solid color. None of these routines can use
// patterns directly, but it is entirely possible to have a pattern draw to an
// off-screen canvas and then draw a shape based on that canvas. As a little
// bonus, you can save the canvas for later so you don't have to render the
// pattern again when you need to redraw the shape.
package shapes

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package shapes
import "art"
import "math"
import "image"
import "image/color"
// TODO: redo fill ellipse, stroke ellipse, etc. so that it only takes in
// destination and source, using the bounds of destination as the bounds of the
// ellipse and the bounds of source as the "clipping rectangle". Line up the Min
// of both canvases.
func FillEllipse (
destination art.Canvas,
source art.Canvas,
bounds image.Rectangle,
) (
updatedRegion image.Rectangle,
) {
dstData, dstStride := destination.Buffer()
srcData, srcStride := source.Buffer()
offset := source.Bounds().Min.Sub(destination.Bounds().Min)
drawBounds :=
source.Bounds().Sub(offset).
Intersect(destination.Bounds()).
Intersect(bounds)
if bounds.Empty() { return }
updatedRegion = bounds
point := image.Point { }
for point.Y = drawBounds.Min.Y; point.Y < drawBounds.Max.Y; point.Y ++ {
for point.X = drawBounds.Min.X; point.X < drawBounds.Max.X; point.X ++ {
if inEllipse(point, bounds) {
offsetPoint := point.Add(offset)
dstIndex := point.X + point.Y * dstStride
srcIndex := offsetPoint.X + offsetPoint.Y * srcStride
dstData[dstIndex] = srcData[srcIndex]
}
}}
return
}
func StrokeEllipse (
destination art.Canvas,
source art.Canvas,
bounds image.Rectangle,
weight int,
) {
if weight < 1 { return }
dstData, dstStride := destination.Buffer()
srcData, srcStride := source.Buffer()
drawBounds := destination.Bounds().Inset(weight - 1)
offset := source.Bounds().Min.Sub(destination.Bounds().Min)
if drawBounds.Empty() { return }
context := ellipsePlottingContext {
plottingContext: plottingContext {
dstData: dstData,
dstStride: dstStride,
srcData: srcData,
srcStride: srcStride,
weight: weight,
offset: offset,
bounds: bounds,
},
radii: image.Pt(drawBounds.Dx() / 2, drawBounds.Dy() / 2),
}
context.center = drawBounds.Min.Add(context.radii)
context.plotEllipse()
}
type ellipsePlottingContext struct {
plottingContext
radii image.Point
center image.Point
}
func (context ellipsePlottingContext) plotEllipse () {
x := float64(0)
y := float64(context.radii.Y)
// region 1 decision parameter
decision1 :=
float64(context.radii.Y * context.radii.Y) -
float64(context.radii.X * context.radii.X * context.radii.Y) +
(0.25 * float64(context.radii.X) * float64(context.radii.X))
decisionX := float64(2 * context.radii.Y * context.radii.Y * int(x))
decisionY := float64(2 * context.radii.X * context.radii.X * int(y))
// draw region 1
for decisionX < decisionY {
points := []image.Point {
image.Pt(-int(x) + context.center.X, -int(y) + context.center.Y),
image.Pt( int(x) + context.center.X, -int(y) + context.center.Y),
image.Pt(-int(x) + context.center.X, int(y) + context.center.Y),
image.Pt( int(x) + context.center.X, int(y) + context.center.Y),
}
if context.srcData == nil {
context.plotColor(points[0])
context.plotColor(points[1])
context.plotColor(points[2])
context.plotColor(points[3])
} else {
context.plotSource(points[0])
context.plotSource(points[1])
context.plotSource(points[2])
context.plotSource(points[3])
}
if (decision1 < 0) {
x ++
decisionX += float64(2 * context.radii.Y * context.radii.Y)
decision1 += decisionX + float64(context.radii.Y * context.radii.Y)
} else {
x ++
y --
decisionX += float64(2 * context.radii.Y * context.radii.Y)
decisionY -= float64(2 * context.radii.X * context.radii.X)
decision1 +=
decisionX - decisionY +
float64(context.radii.Y * context.radii.Y)
}
}
// region 2 decision parameter
decision2 :=
float64(context.radii.Y * context.radii.Y) * (x + 0.5) * (x + 0.5) +
float64(context.radii.X * context.radii.X) * (y - 1) * (y - 1) -
float64(context.radii.X * context.radii.X * context.radii.Y * context.radii.Y)
// draw region 2
for y >= 0 {
points := []image.Point {
image.Pt( int(x) + context.center.X, int(y) + context.center.Y),
image.Pt(-int(x) + context.center.X, int(y) + context.center.Y),
image.Pt( int(x) + context.center.X, -int(y) + context.center.Y),
image.Pt(-int(x) + context.center.X, -int(y) + context.center.Y),
}
if context.srcData == nil {
context.plotColor(points[0])
context.plotColor(points[1])
context.plotColor(points[2])
context.plotColor(points[3])
} else {
context.plotSource(points[0])
context.plotSource(points[1])
context.plotSource(points[2])
context.plotSource(points[3])
}
if decision2 > 0 {
y --
decisionY -= float64(2 * context.radii.X * context.radii.X)
decision2 += float64(context.radii.X * context.radii.X) - decisionY
} else {
y --
x ++
decisionX += float64(2 * context.radii.Y * context.radii.Y)
decisionY -= float64(2 * context.radii.X * context.radii.X)
decision2 +=
decisionX - decisionY +
float64(context.radii.X * context.radii.X)
}
}
}
// FillColorEllipse fills an ellipse within the destination canvas with a solid
// color.
func FillColorEllipse (
destination art.Canvas,
color color.RGBA,
bounds image.Rectangle,
) (
updatedRegion image.Rectangle,
) {
dstData, dstStride := destination.Buffer()
realBounds := bounds
bounds = bounds.Intersect(destination.Bounds()).Canon()
if bounds.Empty() { return }
updatedRegion = bounds
point := image.Point { }
for point.Y = bounds.Min.Y; point.Y < bounds.Max.Y; point.Y ++ {
for point.X = bounds.Min.X; point.X < bounds.Max.X; point.X ++ {
if inEllipse(point, realBounds) {
dstData[point.X + point.Y * dstStride] = color
}
}}
return
}
// StrokeColorEllipse is similar to FillColorEllipse, but it draws an inset
// outline of an ellipse instead.
func StrokeColorEllipse (
destination art.Canvas,
color color.RGBA,
bounds image.Rectangle,
weight int,
) (
updatedRegion image.Rectangle,
) {
if weight < 1 { return }
dstData, dstStride := destination.Buffer()
insetBounds := bounds.Inset(weight - 1)
context := ellipsePlottingContext {
plottingContext: plottingContext {
dstData: dstData,
dstStride: dstStride,
color: color,
weight: weight,
bounds: bounds.Intersect(destination.Bounds()),
},
radii: image.Pt(insetBounds.Dx() / 2, insetBounds.Dy() / 2),
}
context.center = insetBounds.Min.Add(context.radii)
context.plotEllipse()
return
}
func inEllipse (point image.Point, bounds image.Rectangle) bool {
point = point.Sub(bounds.Min)
x := (float64(point.X) + 0.5) / float64(bounds.Dx()) - 0.5
y := (float64(point.Y) + 0.5) / float64(bounds.Dy()) - 0.5
return math.Hypot(x, y) <= 0.5
}

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package shapes
import "art"
import "image"
import "image/color"
// ColorLine draws a line from one point to another with the specified weight
// and color.
func ColorLine (
destination art.Canvas,
color color.RGBA,
weight int,
min image.Point,
max image.Point,
) (
updatedRegion image.Rectangle,
) {
updatedRegion = image.Rectangle { Min: min, Max: max }.Canon()
updatedRegion.Max.X ++
updatedRegion.Max.Y ++
data, stride := destination.Buffer()
bounds := destination.Bounds()
context := linePlottingContext {
plottingContext: plottingContext {
dstData: data,
dstStride: stride,
color: color,
weight: weight,
bounds: bounds,
},
min: min,
max: max,
}
if abs(max.Y - min.Y) < abs(max.X - min.X) {
if max.X < min.X { context.swap() }
context.lineLow()
} else {
if max.Y < min.Y { context.swap() }
context.lineHigh()
}
return
}
type linePlottingContext struct {
plottingContext
min image.Point
max image.Point
}
func (context *linePlottingContext) swap () {
temp := context.max
context.max = context.min
context.min = temp
}
func (context linePlottingContext) lineLow () {
deltaX := context.max.X - context.min.X
deltaY := context.max.Y - context.min.Y
yi := 1
if deltaY < 0 {
yi = -1
deltaY *= -1
}
D := (2 * deltaY) - deltaX
point := context.min
for ; point.X < context.max.X; point.X ++ {
context.plotColor(point)
if D > 0 {
D += 2 * (deltaY - deltaX)
point.Y += yi
} else {
D += 2 * deltaY
}
}
}
func (context linePlottingContext) lineHigh () {
deltaX := context.max.X - context.min.X
deltaY := context.max.Y - context.min.Y
xi := 1
if deltaX < 0 {
xi = -1
deltaX *= -1
}
D := (2 * deltaX) - deltaY
point := context.min
for ; point.Y < context.max.Y; point.Y ++ {
context.plotColor(point)
if D > 0 {
point.X += xi
D += 2 * (deltaX - deltaY)
} else {
D += 2 * deltaX
}
}
}
func abs (n int) int {
if n < 0 { n *= -1}
return n
}

47
shapes/plot.go Normal file
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package shapes
import "image"
import "image/color"
// FIXME? drawing a ton of overlapping squares might be a bit wasteful.
type plottingContext struct {
dstData []color.RGBA
dstStride int
srcData []color.RGBA
srcStride int
color color.RGBA
weight int
offset image.Point
bounds image.Rectangle
}
func (context plottingContext) square (center image.Point) (square image.Rectangle) {
return image.Rect(0, 0, context.weight, context.weight).
Sub(image.Pt(context.weight / 2, context.weight / 2)).
Add(center).
Intersect(context.bounds)
}
func (context plottingContext) plotColor (center image.Point) {
square := context.square(center)
for y := square.Min.Y; y < square.Max.Y; y ++ {
for x := square.Min.X; x < square.Max.X; x ++ {
context.dstData[x + y * context.dstStride] = context.color
}}
}
func (context plottingContext) plotSource (center image.Point) {
square := context.square(center)
for y := square.Min.Y; y < square.Max.Y; y ++ {
for x := square.Min.X; x < square.Max.X; x ++ {
// we offset srcIndex here because we have already applied the
// offset to the square, and we need to reverse that to get the
// proper source coordinates.
srcIndex :=
x + context.offset.X +
(y + context.offset.Y) * context.dstStride
dstIndex := x + y * context.dstStride
context.dstData[dstIndex] = context.srcData [srcIndex]
}}
}

130
shapes/rectangle.go Normal file
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package shapes
import "art"
import "image"
import "art/shatter"
import "image/color"
// TODO: return updatedRegion for all routines in this package
func FillRectangle (
destination art.Canvas,
source art.Canvas,
bounds image.Rectangle,
) (
updatedRegion image.Rectangle,
) {
dstData, dstStride := destination.Buffer()
srcData, srcStride := source.Buffer()
offset := source.Bounds().Min.Sub(destination.Bounds().Min)
drawBounds :=
source.Bounds().Sub(offset).
Intersect(destination.Bounds()).
Intersect(bounds)
if drawBounds.Empty() { return }
updatedRegion = drawBounds
point := image.Point { }
for point.Y = drawBounds.Min.Y; point.Y < drawBounds.Max.Y; point.Y ++ {
for point.X = drawBounds.Min.X; point.X < drawBounds.Max.X; point.X ++ {
offsetPoint := point.Add(offset)
dstIndex := point.X + point.Y * dstStride
srcIndex := offsetPoint.X + offsetPoint.Y * srcStride
dstData[dstIndex] = srcData[srcIndex]
}}
return
}
func StrokeRectangle (
destination art.Canvas,
source art.Canvas,
bounds image.Rectangle,
weight int,
) (
updatedRegion image.Rectangle,
) {
insetBounds := bounds.Inset(weight)
if insetBounds.Empty() {
return FillRectangle(destination, source, bounds)
}
return FillRectangleShatter(destination, source, bounds, insetBounds)
}
// FillRectangleShatter is like FillRectangle, but it does not draw in areas
// specified in "rocks".
func FillRectangleShatter (
destination art.Canvas,
source art.Canvas,
bounds image.Rectangle,
rocks ...image.Rectangle,
) (
updatedRegion image.Rectangle,
) {
tiles := shatter.Shatter(bounds, rocks...)
for _, tile := range tiles {
FillRectangle (
art.Cut(destination, tile),
source, tile)
updatedRegion = updatedRegion.Union(tile)
}
return
}
// FillColorRectangle fills a rectangle within the destination canvas with a
// solid color.
func FillColorRectangle (
destination art.Canvas,
color color.RGBA,
bounds image.Rectangle,
) (
updatedRegion image.Rectangle,
) {
dstData, dstStride := destination.Buffer()
bounds = bounds.Canon().Intersect(destination.Bounds())
if bounds.Empty() { return }
updatedRegion = bounds
for y := bounds.Min.Y; y < bounds.Max.Y; y ++ {
for x := bounds.Min.X; x < bounds.Max.X; x ++ {
dstData[x + y * dstStride] = color
}}
return
}
// FillColorRectangleShatter is like FillColorRectangle, but it does not draw in
// areas specified in "rocks".
func FillColorRectangleShatter (
destination art.Canvas,
color color.RGBA,
bounds image.Rectangle,
rocks ...image.Rectangle,
) (
updatedRegion image.Rectangle,
) {
tiles := shatter.Shatter(bounds, rocks...)
for _, tile := range tiles {
FillColorRectangle(destination, color, tile)
updatedRegion = updatedRegion.Union(tile)
}
return
}
// StrokeColorRectangle is similar to FillColorRectangle, but it draws an inset
// outline of the given rectangle instead.
func StrokeColorRectangle (
destination art.Canvas,
color color.RGBA,
bounds image.Rectangle,
weight int,
) (
updatedRegion image.Rectangle,
) {
insetBounds := bounds.Inset(weight)
if insetBounds.Empty() {
return FillColorRectangle(destination, color, bounds)
}
return FillColorRectangleShatter(destination, color, bounds, insetBounds)
}

97
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// Package shatter provides boolean operations for image.Rectangle.
package shatter
import "image"
// Shatter takes in a bounding rectangle, and several rectangles to be
// subtracted from it. It returns a slice of rectangles that tile together to
// make up the difference between them. This is intended to be used for figuring
// out which areas of a container element's background are covered by other
// elements so it doesn't waste CPU cycles drawing to those areas.
func Shatter (
glass image.Rectangle,
rocks ...image.Rectangle,
) (
tiles []image.Rectangle,
) {
// in this function, the metaphor of throwing several rocks at a sheet
// of glass is used to illustrate the concept.
tiles = []image.Rectangle { glass }
for _, rock := range rocks {
// check each tile to see if the rock has collided with it
tileLen := len(tiles)
for tileIndex := 0; tileIndex < tileLen; tileIndex ++ {
tile := tiles[tileIndex]
if !rock.Overlaps(tile) { continue }
newTiles, n := shatterOnce(tile, rock)
if n > 0 {
// the tile was shattered into one or more sub
// tiles
tiles[tileIndex] = newTiles[0]
tiles = append(tiles, newTiles[1:n]...)
} else {
// the tile was entirely obscured by the rock
// and must be wholly removed
tiles = remove(tiles, tileIndex)
tileIndex --
tileLen --
}
}
}
return
}
func shatterOnce (glass, rock image.Rectangle) (tiles [4]image.Rectangle, n int) {
rock = rock.Intersect(glass)
// |'''''''''''|
// | |
// |###|'''| |
// |###|___| |
// | |
// |___________|
if rock.Min.X > glass.Min.X { tiles[n] = image.Rect (
glass.Min.X, rock.Min.Y,
rock.Min.X, rock.Max.Y,
); n ++ }
// |'''''''''''|
// | |
// | |'''|###|
// | |___|###|
// | |
// |___________|
if rock.Max.X < glass.Max.X { tiles[n] = image.Rect (
rock.Max.X, rock.Min.Y,
glass.Max.X, rock.Max.Y,
); n ++ }
// |###########|
// |###########|
// | |'''| |
// | |___| |
// | |
// |___________|
if rock.Min.Y > glass.Min.Y { tiles[n] = image.Rect (
glass.Min.X, glass.Min.Y,
glass.Max.X, rock.Min.Y,
); n ++ }
// |'''''''''''|
// | |
// | |'''| |
// | |___| |
// |###########|
// |###########|
if rock.Max.Y < glass.Max.Y { tiles[n] = image.Rect (
glass.Min.X, rock.Max.Y,
glass.Max.X, glass.Max.Y,
); n ++ }
return
}
func remove[ELEMENT any] (slice []ELEMENT, s int) []ELEMENT {
return append(slice[:s], slice[s + 1:]...)
}