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context.go
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context.go
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// Copyright 2016, 2017 Florian Pigorsch. All rights reserved.
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.
// Package sm (~ static maps) renders static map images from OSM tiles with markers, paths, and filled areas.
package sm
import (
"errors"
"image"
"image/draw"
"log"
"math"
"github.com/fogleman/gg"
"github.com/golang/geo/s2"
)
// Context holds all information about the map image that is to be rendered
type Context struct {
width int
height int
hasZoom bool
zoom int
hasCenter bool
center s2.LatLng
hasBoundingBox bool
boundingBox s2.Rect
markers []*Marker
paths []*Path
areas []*Area
tileProvider *TileProvider
}
// NewContext creates a new instance of Context
func NewContext() *Context {
t := new(Context)
t.width = 512
t.height = 512
t.hasZoom = false
t.hasCenter = false
t.hasBoundingBox = false
t.tileProvider = NewTileProviderOpenStreetMaps()
return t
}
// SetTileProvider sets the TileProvider to be used
func (m *Context) SetTileProvider(t *TileProvider) {
m.tileProvider = t
}
// SetSize sets the size of the generated image
func (m *Context) SetSize(width, height int) {
m.width = width
m.height = height
}
// SetZoom sets the zoom level
func (m *Context) SetZoom(zoom int) {
m.zoom = zoom
m.hasZoom = true
}
// SetCenter sets the center coordinates
func (m *Context) SetCenter(center s2.LatLng) {
m.center = center
m.hasCenter = true
}
// SetBoundingBox sets the bounding box
func (m *Context) SetBoundingBox(bbox s2.Rect) {
m.boundingBox = bbox
m.hasBoundingBox = true
}
// AddMarker adds a marker to the Context
func (m *Context) AddMarker(marker *Marker) {
m.markers = append(m.markers, marker)
}
// ClearMarkers removes all markers from the Context
func (m *Context) ClearMarkers() {
m.markers = nil
}
// AddPath adds a path to the Context
func (m *Context) AddPath(path *Path) {
m.paths = append(m.paths, path)
}
// ClearPaths removes all paths from the Context
func (m *Context) ClearPaths() {
m.paths = nil
}
// AddArea adds an area to the Context
func (m *Context) AddArea(area *Area) {
m.areas = append(m.areas, area)
}
// ClearAreas removes all areas from the Context
func (m *Context) ClearAreas() {
m.areas = nil
}
func (m *Context) determineBounds() s2.Rect {
r := s2.EmptyRect()
for _, marker := range m.markers {
r = r.Union(marker.bounds())
}
for _, path := range m.paths {
r = r.Union(path.bounds())
}
for _, area := range m.areas {
r = r.Union(area.bounds())
}
return r
}
func (m *Context) determineExtraMarginPixels() float64 {
p := 0.0
for _, marker := range m.markers {
if pp := marker.extraMarginPixels(); pp > p {
p = pp
}
}
for _, path := range m.paths {
if pp := path.extraMarginPixels(); pp > p {
p = pp
}
}
for _, area := range m.areas {
if pp := area.extraMarginPixels(); pp > p {
p = pp
}
}
return p
}
func (m *Context) determineZoom(bounds s2.Rect, center s2.LatLng) int {
b := bounds.AddPoint(center)
if b.IsEmpty() || b.IsPoint() {
return 15
}
tileSize := m.tileProvider.TileSize
margin := 4.0 + m.determineExtraMarginPixels()
w := (float64(m.width) - 2.0*margin) / float64(tileSize)
h := (float64(m.height) - 2.0*margin) / float64(tileSize)
minX := (b.Lo().Lng.Degrees() + 180.0) / 360.0
maxX := (b.Hi().Lng.Degrees() + 180.0) / 360.0
minY := (1.0 - math.Log(math.Tan(b.Lo().Lat.Radians())+(1.0/math.Cos(b.Lo().Lat.Radians())))/math.Pi) / 2.0
maxY := (1.0 - math.Log(math.Tan(b.Hi().Lat.Radians())+(1.0/math.Cos(b.Hi().Lat.Radians())))/math.Pi) / 2.0
dx := maxX - minX
for dx < 0 {
dx = dx + 1
}
for dx > 1 {
dx = dx - 1
}
dy := math.Abs(maxY - minY)
zoom := 1
for zoom < 30 {
tiles := float64(uint(1) << uint(zoom))
if dx*tiles > w || dy*tiles > h {
return zoom - 1
}
zoom = zoom + 1
}
return 15
}
func (m *Context) determineZoomCenter() (int, s2.LatLng, error) {
bounds := m.determineBounds()
if m.hasBoundingBox && !m.boundingBox.IsEmpty() {
center := m.boundingBox.Center()
return m.determineZoom(m.boundingBox, center), center, nil
} else if m.hasCenter {
if m.hasZoom {
return m.zoom, m.center, nil
}
return m.determineZoom(bounds, m.center), m.center, nil
} else if !bounds.IsEmpty() {
center := bounds.Center()
if m.hasZoom {
return m.zoom, center, nil
}
return m.determineZoom(bounds, center), center, nil
}
return 0, s2.LatLngFromDegrees(0, 0), errors.New("Cannot determine map extent: no center coordinates given, no bounding box given, no content (markers, paths, areas) given")
}
type transformer struct {
zoom int
tileSize int
pWidth, pHeight int
pCenterX, pCenterY int
tCountX, tCountY int
tCenterX, tCenterY float64
tOriginX, tOriginY int
}
func newTransformer(width int, height int, zoom int, llCenter s2.LatLng, tileSize int) *transformer {
t := new(transformer)
t.zoom = zoom
t.tileSize = tileSize
t.tCenterX, t.tCenterY = t.ll2t(llCenter)
ww := float64(width) / float64(tileSize)
hh := float64(height) / float64(tileSize)
t.tOriginX = int(math.Floor(t.tCenterX - 0.5*ww))
t.tOriginY = int(math.Floor(t.tCenterY - 0.5*hh))
t.tCountX = 1 + int(math.Floor(t.tCenterX+0.5*ww)) - t.tOriginX
t.tCountY = 1 + int(math.Floor(t.tCenterY+0.5*hh)) - t.tOriginY
t.pWidth = t.tCountX * tileSize
t.pHeight = t.tCountY * tileSize
t.pCenterX = int((t.tCenterX - float64(t.tOriginX)) * float64(tileSize))
t.pCenterY = int((t.tCenterY - float64(t.tOriginY)) * float64(tileSize))
return t
}
func (t *transformer) ll2t(ll s2.LatLng) (float64, float64) {
tiles := math.Exp2(float64(t.zoom))
x := tiles * (ll.Lng.Degrees() + 180.0) / 360.0
y := tiles * (1 - math.Log(math.Tan(ll.Lat.Radians())+(1.0/math.Cos(ll.Lat.Radians())))/math.Pi) / 2.0
return x, y
}
func (t *transformer) ll2p(ll s2.LatLng) (float64, float64) {
x, y := t.ll2t(ll)
if x < float64(t.tOriginX) {
x = x + math.Exp2(float64(t.zoom))
}
x = float64(t.pCenterX) + (x-t.tCenterX)*float64(t.tileSize)
y = float64(t.pCenterY) + (y-t.tCenterY)*float64(t.tileSize)
return x, y
}
// Render actually renders the map image including all map objects (markers, paths, areas)
func (m *Context) Render() (image.Image, error) {
zoom, center, err := m.determineZoomCenter()
if err != nil {
return nil, err
}
tileSize := m.tileProvider.TileSize
trans := newTransformer(m.width, m.height, zoom, center, tileSize)
img := image.NewRGBA(image.Rect(0, 0, trans.pWidth, trans.pHeight))
gc := gg.NewContextForRGBA(img)
// fetch and draw tiles to img
t := NewTileFetcher(m.tileProvider)
tiles := (1 << uint(zoom))
for xx := 0; xx < trans.tCountX; xx++ {
x := trans.tOriginX + xx
if x < 0 {
x = x + tiles
} else if x >= tiles {
x = x - tiles
}
for yy := 0; yy < trans.tCountY; yy++ {
y := trans.tOriginY + yy
if y < 0 || y >= tiles {
log.Printf("Skipping out of bounds tile %d/%d", x, y)
} else {
if tileImg, err := t.Fetch(zoom, x, y); err == nil {
gc.DrawImage(tileImg, xx*tileSize, yy*tileSize)
} else {
log.Printf("Error downloading tile file: %s", err)
}
}
}
}
// draw map objects
for _, area := range m.areas {
area.draw(gc, trans)
}
for _, path := range m.paths {
path.draw(gc, trans)
}
for _, marker := range m.markers {
marker.draw(gc, trans)
}
// crop image
croppedImg := image.NewRGBA(image.Rect(0, 0, int(m.width), int(m.height)))
draw.Draw(croppedImg, image.Rect(0, 0, int(m.width), int(m.height)),
img, image.Point{trans.pCenterX - int(m.width)/2, trans.pCenterY - int(m.height)/2},
draw.Src)
// draw attribution
_, textHeight := gc.MeasureString(m.tileProvider.Attribution)
boxHeight := textHeight + 4.0
gc = gg.NewContextForRGBA(croppedImg)
gc.SetRGBA(0.0, 0.0, 0.0, 0.5)
gc.DrawRectangle(0.0, float64(m.height)-boxHeight, float64(m.width), boxHeight)
gc.Fill()
gc.SetRGBA(1.0, 1.0, 1.0, 0.75)
gc.DrawString(m.tileProvider.Attribution, 4.0, float64(m.height)-4.0)
return croppedImg, nil
}