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Port the media layout algorithm from the Android app #992

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Port the media layout algorithm from the Android app #992

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0a35a44
Port the media layout algorithm from the Android app
grishka Mar 27, 2023
2368997
I forgot to delete a file I ended up not needing
grishka Mar 27, 2023
0d2434b
Also forgot to delete commented out code
grishka Mar 27, 2023
8145c0e
Apply suggestions from code review
grishka Mar 27, 2023
2678e12
Fix indents
grishka Mar 27, 2023
bf304d1
Fix formatting & apply code review suggestions
grishka Mar 27, 2023
a6cd569
Limit aspect ratio to 9:20
grishka Mar 30, 2023
03abd38
Fix layout breaking itself due to view reuse
grishka Mar 30, 2024
a7703be
Remove extra indents
grishka Mar 30, 2024
3ce2929
Improve the case of two horizontal attachments
grishka Apr 2, 2024
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314 changes: 314 additions & 0 deletions MastodonSDK/Sources/MastodonUI/Helper/MediaLayoutHelper.swift
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//
// MediaLayoutHelper.swift
//
//
// Created by Grishka on 25.03.2023.
//

import Foundation
import MastodonSDK
import CoreDataStack

public struct MediaLayoutResult {
let width: Int
let height: Int
let columnSizes: [Int]
let rowSizes: [Int]
let tiles: [Tile]

public struct Tile {
var colSpan: Int
let rowSpan: Int
var startCol: Int
let startRow: Int
var width: Int = 0
}
}

class MediaLayoutHelper {
static let maxWidth: Float = 1000
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static let maxHeight: Float = 1777
static let minHeight: Float = 563
static let gap: Float = 1.5
static let maxRatio = maxWidth / maxHeight

public static func generateMediaLayout(attachments: [MastodonAttachment]) -> MediaLayoutResult? {
if attachments.count<2 {
return nil
}

var ratios: [Float] = []
var allAreWide = true
var allAreSquare = true
for att in attachments {
let ratio: Float = Float(att.size.width/att.size.height)
if ratio <= 1.2 {
allAreWide = false
if ratio<0.8 {
allAreSquare = false
}
} else {
allAreSquare = false
}
ratios.append(ratio)
}

let avgRatio: Float = ratios.reduce(0.0, +) / Float(ratios.count)

switch attachments.count {
case 2:
if allAreWide && avgRatio>1.4*maxRatio && (ratios[1]-ratios[0])<0.2 {
// Two wide attachments, one above the other
let h = Int(max(min(maxWidth/ratios[0], min(maxWidth/ratios[1], (maxHeight-gap)/2.0)), minHeight/2.0).rounded())

return MediaLayoutResult(width: Int(maxWidth),
height: Int((Float(h)*2.0+gap).rounded()),
columnSizes: [Int(maxWidth)],
rowSizes: [h, h],
tiles: [
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 0, startRow: 0),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 0, startRow: 1)
])
} else if allAreWide || allAreSquare {
// Next to each other, same ratio
let w: Float = (maxWidth-gap) / 2.0
let h: Float = max(min(w/ratios[0], min(w/ratios[1], maxHeight)), minHeight)

let wInt: Int = Int(w.rounded())
let hInt: Int = Int(h.rounded())

return MediaLayoutResult(width: Int(maxWidth),
height: hInt,
columnSizes: [wInt, Int(maxWidth)-wInt],
rowSizes: [hInt],
tiles: [
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 0, startRow: 0),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 1, startRow: 0)
])
} else {
// Next to each other, different ratios
let w0: Float = ((maxWidth - gap) / ratios[1] / (1.0 / ratios[0] + 1.0 / ratios[1]))
let w1: Float = maxWidth - w0 - gap
let h: Float = max(min(maxHeight, min(w0/ratios[0], w1/ratios[1])), minHeight)

let w0Int = Int(w0.rounded())
let w1Int = Int(w1.rounded())
let hInt = Int(h.rounded())

return MediaLayoutResult(width: Int((w0+w1+gap).rounded()),
height: hInt,
columnSizes: [w0Int, w1Int],
rowSizes: [hInt],
tiles: [
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 0, startRow: 0),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 1, startRow: 0)
])
}
case 3:
if ratios[0]>1.2*maxRatio || avgRatio>1.5*maxRatio || allAreWide {
// One above two smaller ones
var hCover: Float = min(maxWidth/ratios[0], (maxHeight-gap)*0.66)
let w2: Float = (maxWidth-gap)/2.0
var h: Float = min(maxHeight-hCover-gap, min(w2/ratios[1], w2/ratios[2]))
if hCover+h < minHeight {
let prevTotalHeight = hCover+h
hCover = minHeight*(hCover/prevTotalHeight)
h = minHeight*(h/prevTotalHeight)
}

return MediaLayoutResult(width: Int(maxWidth),
height: Int((hCover+h+gap).rounded()),
columnSizes: [Int(w2.rounded()), Int(maxWidth-w2.rounded())],
rowSizes: [Int(hCover.rounded()), Int(h.rounded())],
tiles: [
MediaLayoutResult.Tile(colSpan: 2, rowSpan: 1, startCol: 0, startRow: 0),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 0, startRow: 1),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 1, startRow: 1)
])
} else {
// One on the left, two smaller ones on the right
let height: Float = min(maxHeight, maxWidth*0.66/avgRatio)
let wCover: Float = min(height*ratios[0], (maxWidth-gap)*0.66)
let h1: Float = ratios[1]*(height-gap)/(ratios[2]+ratios[1])
let h0: Float = height-h1-gap
let w: Float = min(maxWidth-wCover-gap, h1*ratios[2], h0*ratios[1])

return MediaLayoutResult(width: Int((wCover+w+gap).rounded()),
height: Int(height.rounded()),
columnSizes: [Int(wCover.rounded()), Int(w.rounded())],
rowSizes: [Int(h0.rounded()), Int(h1.rounded())],
tiles: [
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 2, startCol: 0, startRow: 0),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 1, startRow: 0),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 1, startRow: 1)
])
}
case 4:
if ratios[0]>1.2*maxRatio || avgRatio>1.5*maxRatio || allAreWide {
// One above three smaller ones
var hCover: Float = min(maxWidth/ratios[0], (maxHeight-gap)*0.66)
var h: Float = (maxWidth-2.0*gap)/(ratios[1]+ratios[2]+ratios[3])
let w0: Float = h*ratios[1]
let w1: Float = h*ratios[2]
h = min(maxHeight-hCover-gap, h)
if hCover+h<minHeight {
let prevTotalHeight = hCover+h
hCover = minHeight*(hCover/prevTotalHeight)
h = minHeight*(h/prevTotalHeight)
}

return MediaLayoutResult(width: Int(maxWidth),
height: Int((hCover+h+gap).rounded()),
columnSizes: [Int(w0.rounded()), Int(w1.rounded()), Int(maxWidth-w0.rounded()-w1.rounded())],
rowSizes: [Int(hCover.rounded()), Int(h.rounded())],
tiles: [
MediaLayoutResult.Tile(colSpan: 3, rowSpan: 1, startCol: 0, startRow: 0),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 0, startRow: 1),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 1, startRow: 1),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 2, startRow: 1)
])
} else {
// One on the left, three smaller ones on the right
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Does this mean 4 attachments will never be rendered as a 2x2 grid?

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Yes, it's always 1 bigger one and 3 smaller ones

let height: Float = min(maxHeight, maxWidth*0.66/avgRatio)
let wCover: Float = min(height*ratios[0], (maxWidth-gap)*0.66)
var w: Float = (height-2.0*gap)/(1.0/ratios[1]+1.0/ratios[2]+1.0/ratios[3])
let h0: Float = w/ratios[1]
let h1: Float = w/ratios[2]
let h2: Float = w/ratios[3]+gap
w = min(maxWidth-wCover-gap, w)

return MediaLayoutResult(width: Int((wCover+gap+w).rounded()),
height: Int(height.rounded()),
columnSizes: [Int(wCover.rounded()), Int(w.rounded())],
rowSizes: [Int(h0.rounded()), Int(h1.rounded()), Int(h2.rounded())],
tiles: [
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 3, startCol: 0, startRow: 0),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 1, startRow: 0),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 1, startRow: 1),
MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 1, startRow: 2)
])
}
default:
let cnt = attachments.count
var ratiosCropped: [Float] = []
if avgRatio>1.1 {
for ratio in ratios {
ratiosCropped.append(max(1.0, ratio))
}
} else {
for ratio in ratios {
ratiosCropped.append(min(1.0, ratio))
}
}

var tries: [[Int]: [Float]] = [:]

// One line
tries[[attachments.count]] = [calculateMultiThumbsHeight(ratios: ratiosCropped, width: maxWidth, margin: gap)]

// Two lines
for firstLine in 1...cnt-1 {
tries[[firstLine, cnt-firstLine]] = [
calculateMultiThumbsHeight(ratios: Array(ratiosCropped[..<firstLine]), width: maxWidth, margin: gap),
calculateMultiThumbsHeight(ratios: Array(ratiosCropped[firstLine...]), width: maxWidth, margin: gap)
]
}

// Three lines
for firstLine in 1...cnt-2 {
for secondLine in 1...cnt-firstLine-1 {
tries[[firstLine, secondLine, cnt-firstLine-secondLine]] = [
calculateMultiThumbsHeight(ratios: Array(ratiosCropped[..<firstLine]), width: maxWidth, margin: gap),
calculateMultiThumbsHeight(ratios: Array(ratiosCropped[firstLine..<firstLine+secondLine]), width: maxWidth, margin: gap),
calculateMultiThumbsHeight(ratios: Array(ratiosCropped[(firstLine+secondLine)...]), width: maxWidth, margin: gap)
]
}
}

let realMaxHeight = min(maxWidth, maxHeight)

var optConf: [Int] = []
var optDiff: Float = Float.greatestFiniteMagnitude

for (conf, heights) in tries {
let confH: Float = heights.reduce(gap*Float(heights.count-1), +)
var confDiff = abs(confH-realMaxHeight)
if conf.count>1 && (conf[0]>conf[1] || (conf.count>2 && conf[1]>conf[2])) {
confDiff *= 1.1
}
if confDiff<optDiff {
optConf = conf
optDiff = confDiff
}
}

var thumbsRemain: [MastodonAttachment] = Array(attachments)
var ratiosRemain: [Float] = Array(ratiosCropped)
let optHeights = tries[optConf]!
var totalHeight: Float = 0.0
var rowSizes: [Int] = []
var gridLineOffsets: [Int] = []
var rowTiles: [[MediaLayoutResult.Tile]] = []

for (i, lineChunksNum) in optConf.enumerated() {
var lineThumbs: [MastodonAttachment] = []
for _ in 0..<lineChunksNum {
lineThumbs.append(thumbsRemain.removeFirst())
}
let lineHeight = optHeights[i]
totalHeight += lineHeight
rowSizes.append(Int(lineHeight.rounded()))
var totalWidth: Int = 0
var row: [MediaLayoutResult.Tile] = []
for (j, _) in lineThumbs.enumerated() {
let thumbRatio = ratiosRemain.removeFirst()
let w: Float = j==lineThumbs.count-1 ? (maxWidth-Float(totalWidth)) : (thumbRatio*lineHeight)
totalWidth += Int(w.rounded())
if j<lineThumbs.count-1 && !gridLineOffsets.contains(totalWidth) {
gridLineOffsets.append(totalWidth)
}
var tile = MediaLayoutResult.Tile(colSpan: 1, rowSpan: 1, startCol: 0, startRow: i)
tile.width = Int(w.rounded())
row.append(tile)
}
rowTiles.append(row)
}

gridLineOffsets = gridLineOffsets.sorted()
gridLineOffsets.append(Int(maxWidth))

var columnSizes: [Int] = [gridLineOffsets[0]]
for (i, offset) in gridLineOffsets[1...].enumerated() {
columnSizes.append(offset - gridLineOffsets[i]) // i is already offset by one here
}

for row in 0..<rowTiles.count {
var columnOffset: Int = 0
for (tile, _) in rowTiles[row].enumerated() {
let startColumn = columnOffset
rowTiles[row][tile].startCol = startColumn
var width: Int = 0
rowTiles[row][tile].colSpan = 0
for i in startColumn..<columnSizes.count {
width += columnSizes[i]
rowTiles[row][tile].colSpan += 1
if width == rowTiles[row][tile].width {
break
}
}
columnOffset += rowTiles[row][tile].colSpan
}
}

return MediaLayoutResult(width: Int(maxWidth),
height: Int((totalHeight+gap*Float(optHeights.count-1)).rounded()),
columnSizes: columnSizes,
rowSizes: rowSizes,
tiles: rowTiles.reduce([], +))
}
}

private static func calculateMultiThumbsHeight(ratios: [Float], width: Float, margin: Float) -> Float {
return (width-(Float(ratios.count)-1.0)*margin)/ratios.reduce(0.0, +)
}
}