DynamicGridLayout - Initial Draft

cmd/dynamicgrid_demo/main.go

@@ -0,0 +1,268 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"math"
+
+	"fyne.io/fyne/v2"
+	"fyne.io/fyne/v2/app"
+	"fyne.io/fyne/v2/canvas"
+	"fyne.io/fyne/v2/container"
+	"fyne.io/fyne/v2/theme"
+	"fyne.io/fyne/v2/widget"
+)
+
+func main() {
+	a := app.New()
+	w := a.NewWindow("Dynamic Grid")
+
+	const numTestItems = 128
+	names := make([]string, 0, numTestItems)
+	for i := 0; i < numTestItems; i++ {
+		name := fmt.Sprintf("Button %d", i)
+		names = append(names, name)
+	}
+	w.SetContent(exampleGridler(names))
+
+	w.ShowAndRun()
+}
+
+func exampleGridler(names []string) *fyne.Container {
+	makeAnItem := func(index int) fyne.CanvasObject {
+		// just to spice things up a bit and show more
+		// how this works
+		if index%10 == 0 {
+			return canvas.NewImageFromResource(theme.FyneLogo())
+		}
+		if index%23 == 0 {
+			pb := widget.NewProgressBarInfinite()
+			pb.Start()
+			return pb
+		}
+		if index == 42 {
+			// fixme this incidentally shows a bug when you slowly change
+			// the window size. this widget is not made/meant for different
+			// sized widgets, however it would be good to handle them properly
+			return container.NewCenter(widget.NewLabel("the meaning of life"))
+		}
+
+		name := names[index]
+		return widget.NewButton(name, func() { fmt.Println(name) })
+	}
+
+	// depending on the widget-heavyness,
+	// you likely want a cache
+	cache := make(map[int]fyne.CanvasObject)
+
+	dataRequester := func(numItems int) []fyne.CanvasObject {
+		objs := make([]fyne.CanvasObject, 0, numItems)
+
+		for _, index := range sampler(len(names), numItems) {
+			cached, ok := cache[index]
+			if !ok {
+				cached = makeAnItem(index)
+				cache[index] = cached
+			}
+
+			objs = append(objs, cached)
+		}
+
+		return objs
+	}
+
+	// we always want at least 2 rows and 2 columns
+	const imagesPerViewRows = 2
+	const imagesPerViewColums = 2
+	return NewDynamicGrid(imagesPerViewRows, imagesPerViewColums, dataRequester)
+}
+
+// makes a stable same-input same-output sampling
+func sampler(maxItems, requiredItems int) []int {
+	if requiredItems > maxItems {
+		indexes := make([]int, maxItems)
+		// in a real scenario we just
+		// would not have more to display
+		// example file previews
+		for index := 0; index < maxItems; index++ {
+			indexes[index] = index
+		}
+		return indexes
+	}
+
+	indexes := make([]int, 0, requiredItems)
+	step := int(float64(maxItems) / float64(requiredItems))
+	found := 0
+	for index := 0; found < requiredItems; index += step {
+		indexes = append(indexes, index)
+		found += 1
+	}
+
+	return indexes
+}
+
+// ----------------------------------------------------------------
+// ----------------------------------------------------------------
+// Currently kept here during heavy development, later to be moved
+// to the layout folder
+
+// do not directly tinker with Container.Objects or Container.Layout
+func NewDynamicGrid(minrows, mincols int, mr MoreRequester) *fyne.Container {
+	grid := newDynamicGridLayout(minrows, mincols, mr)
+	c := container.New(grid)
+	grid.container = c // we need this in the Layout function
+	return c
+}
+
+// Declare conformity with Layout interface
+var _ fyne.Layout = (*dynamicGridLayout)(nil)
+
+type MoreRequester func(numItems int) []fyne.CanvasObject
+type dynamicGridLayout struct {
+	minrows   int
+	mincols   int
+	container *fyne.Container
+	mr        MoreRequester
+}
+
+var ErrorMissingMoreRequester = errors.New("you must provide a MoreRequester function")
+
+// newDynamicGridLayout returns a new dynamic grid layout
+func newDynamicGridLayout(minrows, mincols int, mr MoreRequester) *dynamicGridLayout {
+	// i dont want to recheck this in hotpath Layout ether
+	// fixme go version update replace with max()
+	if minrows < 1 {
+		minrows = 1
+	}
+	if mincols < 1 {
+		mincols = 1
+	}
+	if mr == nil {
+		// fixme whats the nice way to deal with that?
+		// just nop ourselves and return a stackLayout?
+		// nil? but then unexplained not working?
+		// maybe have NewDynamicGrid just return an error?
+		// would mess with cascading
+		panic(ErrorMissingMoreRequester)
+		return nil
+	}
+
+	return &dynamicGridLayout{
+		minrows: minrows,
+		mincols: mincols,
+		mr:      mr,
+	}
+}
+
+// Layout is called to pack all child objects into a specified size.
+// For a DynamicGridLayout this will pack the needed amount of objects
+// into a table format with at least the minumum specified columns and rows
+// and if less content available to fill as much space as possible.
+func (g *dynamicGridLayout) Layout(objects []fyne.CanvasObject, size fyne.Size) {
+	padding := theme.Padding()
+
+	childsize := uniformBlocksize(objects).Add(fyne.NewSquareSize(padding / 2))
+	numcols := numobjfit(size.Width, childsize.Width)
+	numrows := numobjfit(size.Height, childsize.Height)
+	maxamount := numrows * numcols
+
+	objects = g.mr(maxamount)
+	g.container.Objects = objects //otherwise something is salty and we render nothing
+	lenobjects := len(objects)
+
+	if lenobjects < 1 {
+		// nothing to do
+		return
+	}
+	if lenobjects < maxamount {
+		// stretch over available space but evenly
+		numcols, numrows = strechedSizeCalculator(lenobjects, childsize, size)
+		maxamount = numcols * numrows
+	}
+
+	padWidth := float32(numcols-1) * padding
+	padHeight := float32(numrows-1) * padding
+	cellWidth := float32(size.Width-padWidth) / float32(numcols)
+	cellHeight := float32(size.Height-padHeight) / float32(numrows)
+
+	row, col := 0, 0
+	for i, child := range objects {
+		// leading edge top left
+		x1 := (cellWidth + padding) * float32(col)
+		y1 := (cellHeight + padding) * float32(row)
+		// trailing edge bottom right
+		x2 := (cellWidth+padding)*float32(col+1) - padding
+		y2 := (cellHeight+padding)*float32(row+1) - padding
+
+		child.Move(fyne.NewPos(x1, y1))
+		child.Resize(fyne.NewSize(x2-x1, y2-y1))
+
+		if (i+1)%numcols == 0 {
+			row++
+			col = 0
+		} else {
+			col++
+		}
+	}
+}
+
+// MinSize finds the smallest size that satisfies all the child objects.
+// For a DynamicGridLayout this is the size of the largest child object
+// multiplied by the minimum number of columns and rows, with
+// appropriate padding between children.
+func (g *dynamicGridLayout) MinSize(objects []fyne.CanvasObject) fyne.Size {
+	// fixme do we also have to ask for items here?
+	// by visual testing the answer is no
+	minSize := uniformBlocksize(objects)
+	padding := theme.Padding()
+
+	minContentSize := fyne.NewSize(
+		minSize.Width*float32(g.mincols),
+		minSize.Height*float32(g.minrows),
+	)
+	return minContentSize.Add(fyne.NewSize(
+		padding*fyne.Max(float32(g.mincols-1), 0),
+		padding*fyne.Max(float32(g.minrows-1), 0),
+	))
+
+}
+
+func numobjfit(fullsize, childsize float32) int {
+	// fixme go version update replace with max()
+	num := int(math.Floor(float64(fullsize) / float64(childsize)))
+	if num < 1 {
+		return 1
+	}
+	return num
+}
+
+// fixme find a smart way to do this
+// like for real, this cant be it
+func strechedSizeCalculator(numobjects int, childsize fyne.Size, size fyne.Size) (int, int) {
+	if numobjects < 1 {
+		// failsave
+		return 1, 1
+	}
+	var numcols int
+	var numrows int
+	for {
+		childsize = childsize.Add(fyne.NewSquareSize(1))
+		numcols = numobjfit(size.Width, childsize.Width)
+		numrows = numobjfit(size.Height, childsize.Height)
+		if numcols*numrows <= numobjects {
+			childsize = childsize.Subtract(fyne.NewSquareSize(1))
+			numcols = numobjfit(size.Width, childsize.Width)
+			numrows = numobjfit(size.Height, childsize.Height)
+			break
+		}
+	}
+	return numcols, numrows
+}
+
+func uniformBlocksize(objects []fyne.CanvasObject) fyne.Size {
+	childsize := fyne.NewSquareSize(1)
+	for _, child := range objects {
+		childsize = childsize.Max(child.MinSize())
+	}
+	return childsize
+}