gioui.org/ui@v0.0.0-20190926171558-ce74bc0cbaea/app/internal/gpu/pack.go (about)

     1  // SPDX-License-Identifier: Unlicense OR MIT
     2  
     3  package gpu
     4  
     5  import (
     6  	"image"
     7  )
     8  
     9  // packer packs a set of many smaller rectangles into
    10  // much fewer larger atlases.
    11  type packer struct {
    12  	maxDim int
    13  	spaces []image.Rectangle
    14  
    15  	sizes []image.Point
    16  	pos   image.Point
    17  }
    18  
    19  type placement struct {
    20  	Idx int
    21  	Pos image.Point
    22  }
    23  
    24  // add adds the given rectangle to the atlases and
    25  // return the allocated position.
    26  func (p *packer) add(s image.Point) (placement, bool) {
    27  	if place, ok := p.tryAdd(s); ok {
    28  		return place, true
    29  	}
    30  	p.newPage()
    31  	return p.tryAdd(s)
    32  }
    33  
    34  func (p *packer) clear() {
    35  	p.sizes = p.sizes[:0]
    36  	p.spaces = p.spaces[:0]
    37  }
    38  
    39  func (p *packer) newPage() {
    40  	p.pos = image.Point{}
    41  	p.sizes = append(p.sizes, image.Point{})
    42  	p.spaces = p.spaces[:0]
    43  	p.spaces = append(p.spaces, image.Rectangle{
    44  		Max: image.Point{X: p.maxDim, Y: p.maxDim},
    45  	})
    46  }
    47  
    48  func (p *packer) tryAdd(s image.Point) (placement, bool) {
    49  	// Go backwards to prioritize smaller spaces first.
    50  	for i := len(p.spaces) - 1; i >= 0; i-- {
    51  		space := p.spaces[i]
    52  		rightSpace := space.Dx() - s.X
    53  		bottomSpace := space.Dy() - s.Y
    54  		if rightSpace >= 0 && bottomSpace >= 0 {
    55  			// Remove space.
    56  			p.spaces[i] = p.spaces[len(p.spaces)-1]
    57  			p.spaces = p.spaces[:len(p.spaces)-1]
    58  			// Put s in the top left corner and add the (at most)
    59  			// two smaller spaces.
    60  			pos := space.Min
    61  			if bottomSpace > 0 {
    62  				p.spaces = append(p.spaces, image.Rectangle{
    63  					Min: image.Point{X: pos.X, Y: pos.Y + s.Y},
    64  					Max: image.Point{X: space.Max.X, Y: space.Max.Y},
    65  				})
    66  			}
    67  			if rightSpace > 0 {
    68  				p.spaces = append(p.spaces, image.Rectangle{
    69  					Min: image.Point{X: pos.X + s.X, Y: pos.Y},
    70  					Max: image.Point{X: space.Max.X, Y: pos.Y + s.Y},
    71  				})
    72  			}
    73  			idx := len(p.sizes) - 1
    74  			size := &p.sizes[idx]
    75  			if x := pos.X + s.X; x > size.X {
    76  				size.X = x
    77  			}
    78  			if y := pos.Y + s.Y; y > size.Y {
    79  				size.Y = y
    80  			}
    81  			return placement{Idx: idx, Pos: pos}, true
    82  		}
    83  	}
    84  	return placement{}, false
    85  }