/app/app.go

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203*/
204
205package app
206
207import (
208	"appengine"
209	"fmt"
210	"http"
211	"image"
212	"image/draw"
213	"image/jpeg"
214	"image/png"
215	"os"
216	"path/filepath"
217	"strings"
218	"sync"
219)
220
221const (
222	backgroundImageFile = "img/bg/thanksgiving-2011-actual-size-bg-nolinks.png"
223	defaultImageFile    = "img/00000000.png"
224	prefix              = "/thumb/"
225)
226
227var (
228	// dirs maps each layout element to its location on disk.
229	dirs = map[string]string{
230		"h": "img/heads",
231		"b": "img/eyes_beak",
232		"i": "img/index_feathers",
233		"m": "img/middle_feathers",
234		"r": "img/ring_feathers",
235		"p": "img/pinky_feathers",
236		"f": "img/feet",
237		"w": "img/wing",
238	}
239
240	// urlMap maps each URL character position to
241	// its corresponding layout element.
242	urlMap = [...]string{"b", "h", "i", "m", "r", "p", "f", "w"}
243
244	// layoutMap maps each layout element to its position
245	// on the background image.
246	layoutMap = map[string]image.Rectangle{
247		"h": {image.Pt(109, 50), image.Pt(166, 152)},
248		"i": {image.Pt(136, 21), image.Pt(180, 131)},
249		"m": {image.Pt(159, 7), image.Pt(201, 126)},
250		"r": {image.Pt(188, 20), image.Pt(230, 125)},
251		"p": {image.Pt(216, 48), image.Pt(258, 134)},
252		"f": {image.Pt(155, 176), image.Pt(243, 213)},
253		"w": {image.Pt(169, 118), image.Pt(250, 197)},
254		"b": {image.Pt(105, 104), image.Pt(145, 148)},
255	}
256
257	// elements maps each layout element to its images.
258	elements = make(map[string][]*image.RGBA)
259
260	// backgroundImage contains the background image data.
261	backgroundImage *image.RGBA
262
263	// defaultImage is the image that is served if an error occurs. 
264	defaultImage *image.RGBA
265
266	// imageQuality is the encoding quality setting for the output image.
267	imageQuality = jpeg.Options{95}
268)
269
270func init() {
271	http.HandleFunc(prefix, handler)
272}
273
274// handler serves a turkey snapshot for the given request.
275func handler(w http.ResponseWriter, r *http.Request) {
276	// Defer a function to recover from any panics.
277	// When recovering from a panic, log the error condition to
278	// the App Engine dashboard and send the default image to the user.
279	defer func() {
280		if err := recover(); err != nil {
281			c := appengine.NewContext(r)
282			c.Errorf("%s", err)
283			c.Errorf("%s", "Traceback: "+r.RawURL)
284			if defaultImage != nil {
285				w.Header().Set("Content-type", "image/jpeg")
286				jpeg.Encode(w, defaultImage, &imageQuality)
287			}
288		}
289	}()
290
291	// Load images from disk on the first request.
292	loadOnce.Do(load)
293
294	// Make a copy of the background to draw into.
295	bgRect := backgroundImage.Bounds()
296	m := image.NewRGBA(bgRect.Dx(), bgRect.Dy())
297	draw.Draw(m, m.Bounds(), backgroundImage, image.ZP, draw.Over)
298
299	// Process each character of the request string.
300	code := strings.ToLower(r.URL.Path[len(prefix):])
301	for i, p := range code {
302		// Decode hex character p in place.
303		if p < 'a' {
304			// it's a digit
305			p = p - '0'
306		} else {
307			// it's a letter
308			p = p - 'a' + 10
309		}
310
311		t := urlMap[i]    // element type by index
312		em := elements[t] // element images by type
313		if p >= len(em) {
314			panic(fmt.Sprintf("element index out of range %s: "+
315				"%d >= %d", t, p, len(em)))
316		}
317
318		// Draw the element to m,
319		// using the layoutMap to specify its position.
320		draw.Draw(m, layoutMap[t], em[p], image.ZP, draw.Over)
321	}
322
323	// Encode JPEG image and write it as the response.
324	w.Header().Set("Content-type", "image/jpeg")
325	w.Header().Set("cache-control", "public, max-age=259200")
326	jpeg.Encode(w, m, &imageQuality)
327}
328
329
330// loadOnce is used to call the load function only on the first request.
331var loadOnce sync.Once
332
333// load reads the various PNG images from disk and stores them in their
334// corresponding global variables.
335func load() {
336	defaultImage = loadPNG(defaultImageFile)
337	backgroundImage = loadPNG(backgroundImageFile)
338	for dirKey, dir := range dirs {
339		paths, err := filepath.Glob(dir + "/*.png")
340		if err != nil {
341			panic(err)
342		}
343		for _, p := range paths {
344			elements[dirKey] = append(elements[dirKey], loadPNG(p))
345		}
346	}
347}
348
349// loadPNG loads a PNG image from disk and returns it as an *image.RGBA.
350func loadPNG(filename string) *image.RGBA {
351	f, err := os.Open(filename)
352	if err != nil {
353		panic(err)
354	}
355	defer f.Close()
356	m, err := png.Decode(f)
357	if err != nil {
358		panic(err)
359	}
360	return rgba(m)
361}
362
363// rgba converts an image.Image to an *image.RGBA.
364func rgba(m image.Image) *image.RGBA {
365	if r, ok := m.(*image.RGBA); ok {
366		return r
367	}
368	b := m.Bounds()
369	r := image.NewRGBA(b.Dx(), b.Dy())
370	draw.Draw(r, b, m, image.ZP, draw.Src)
371	return r
372}