# Cover Flow view browsing

• posted
0

The Mac finder has a view called cover flow, which looks like this:

Icons/file previews are displayed with the selected one in front and the rest behind on either side.

I'd like to try to emulate this with a custom view class, where square buttons are displayed, each with an image on it. Ideally, the user would be able to swipe in the cover flow view and it would animate as it does on my Mac, then they can tap one to perform an action.

Is this feasible in UI, or is it beyond the scope of UI and I should try to do it in scene? It will ultimately be in a UI, so for scene I would have to use a SceneView. I'm kind of leaning towards using scene because of touch handling, but I wanted to see what other people thought.

• posted
2

Ok, I'm ready to start implementation now.

• posted
1

Please make it a Github repo so that we can add Pythonista-Tools link to it.

• posted
2

Sure, @ccc I'll do that when I'm finished with this bit.

• posted
0

@JonB None of the numbers besides 512 make sense to me as logical fractions of 1024. Where did they come from?

Additionally, the sentence

divide by 1024 and multiply by screen width

is confusing to me, because 1024 IS the screen width... `x/1024*1024 = x`

Also, if it's not a lot of work, could you try to explain the math behind your equations? I don't like to borrow code I don't understand, it's a mini-policy of mine. (No, I don't understand all the code behind all the modules I import, I mean I don't like to insert others' code into my own without understanding it)

• posted
1

Yes you correct re screen width... my point is if you want this to scale for a different screen width, like say 768 in portrait, you would divide by 1024, and multiply by screen width. in retrospect, you could just scale the final numbers.

when i plotted width vs index, and noticed it looked a lot like an exponential decay about the center.. That gives an exp(-abs(i-N/2)) form. The leading factor is the width of the central frame. To get the width at the end, i played with the factor and exponent inside the exponential. Then, i experimented with scaling for more frames, keeping the center width and end width the same. I thought you would still want a big difference betwenn center and next frames, so i played with the exponent.

Likewise, i plotted xc vs w, and saw a similar exponential factor, and again some trial and error. Y vs w appeared very linear, so i just fit a line.

• posted
0

Spent today working on image2ASCII, will get to this tomorrow.

• posted
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I get the feeling I'm using your code wrong. What am I doing that isn't as intended? some of your sentences don't make a lot of sense to me:

the relationship between center and width from the original

I've implemented your code as follows:

``````#Make frames for all views
N = 9
frames = []
for i in range(N):
#Thanks to @JonB for this code.
w=370*exp(-2.4*(abs((i-N/2.0-0.5)/N)**(1.38/N**0.25)))
xc=512+copysign(470.*log(w/370.),i-N/2)
yc= (192-w)
frames.append((xc+.5*w, yc+.5*w, w, w))
``````

Looks pretty good for the first half, the rest are messed up. I feel stupid, but if you could please correct my mistakes that'd be wonderful. (>ლ)

• posted
1

Sorry, I think I made an off-by-one error in the width equation. The `i-N/2.0-0.5` should be `i-N/2.0+0.5`.

Also, I think you want `frames.append((xc-0.5*w, yc-0.5*w,w,w))` instead of +0.5 in both places

• posted
0

Thanks! It actually needed to be `(xc-0.5*w, yc+0.5*w, w, w)` in order for it to work correctly.

• posted
1

by the way, one of the nice things re: the equation is that you can use touch_moved to create continuous motion along the curve. Basically you would associate each image with a index variable, touch_moved generates a fractional index offset added to each one, say, the x part of the motion divided by the center diff, and wrapping around negative values. still use a zero time animatin to sync up the motion. Then touch_ended would round to the nearest index, and do a slower animation to snap everybody in place. You could also use the "velocity" of the last swipe to over scan.

• posted
2

New code, supports different screen sizes, and auto-resizes with device rotation. Also supports arbitrary numbers of images. It will display your images whether you have 1 image or 100. Now running it will also pick random images from the included images to present.

``````# coding: utf-8
import ui
from PIL import Image
from io import BytesIO
from time import sleep
from math import exp, log, copysign, ceil

BGCOLOR = '#0F0F0F'

def pil_to_ui(img):
b = BytesIO()
img.save(b, "PNG")
data = b.getvalue()
b.close()
return ui.Image.from_data(data)

class CoverFlow(ui.View):
def __init__(self, images):
self.images = [pil_to_ui(image) for image in images]
if len(self.images) < 9:
self.images *= int(ceil(9./len(self.images)))
self.frame = (0, 0, 1024, 768)
self.oldframe = (0, 0, 1024)
self.background_color = BGCOLOR
#Make frames for all views
N = 9
frames = []
#Create frames
for i in xrange(N):
#Thanks to @JonB for this code.
w=370/1024.*self.width*exp(-2.4*(abs((i-N/2.0+0.5)/N)**(1.38/N**0.25)))
xc=512/1024.*self.width+copysign(470.0/1024*self.width*log(w/(370.0/1024*self.width)),i-N/2)
yc= (192/1024.*self.width-w)
frames.append((xc-0.5*w, yc+0.5*w, w, w))

#Create subviews for the minimum of 9 images
for index, frame in enumerate(frames):
iv = ui.ImageView(frame=frame)
iv.image = self.images[index]
iv.prev_frame = iv.frame
self.add_subview(iv)
if index > 4:
iv.send_to_back()

#Handle any additional images that are provided
for i in self.images[9:]:
iv9 = ui.ImageView(frame=frames[-1])
iv9.image = i
iv9.prev_frame = iv9.frame
self.add_subview(iv9)
iv9.send_to_back()

def layout(self):
if self.frame != self.oldframe:
N = 9
frames = []
#Create frames
for i in range(N):
#Thanks to @JonB for this code.
w=370/1024.*self.width*exp(-2.4*(abs((i-N/2.0+0.5)/N)**(1.38/N**0.25)))
xc=512/1024.*self.width+copysign(470.0/1024*self.width*log(w/(370.0/1024*self.width)),i-N/2)
yc= (192/1024.*self.width-w)
frames.append((xc-0.5*w, yc+0.5*w, w, w))

for sv in self.subviews:
self.remove_subview(sv)
#Create subviews for the minimum of 9 images
for index, frame in enumerate(frames):
iv = ui.ImageView(frame=frame)
iv.image = self.images[index]
iv.prev_frame = iv.frame
self.add_subview(iv)
if index > 4:
iv.send_to_back()

#Handle any additional images that are provided
for i in self.images[9:]:
iv9 = ui.ImageView(frame=frames[-1])
iv9.image = i
iv9.prev_frame = iv9.frame
self.add_subview(iv9)
iv9.send_to_back()
self.oldframe = self.frame

def anim(self):
#Change frames
len_subviews = len(self.subviews)
for i, sub in enumerate(self.subviews):
next = self.subviews[(i + (1 if self.touch_direction else -1)) % len_subviews]
sub.frame = next.prev_frame
for sub in self.subviews:
sub.prev_frame = sub.frame

#Resort self.images
if self.touch_direction:
self.images = [self.images[-1]]+self.images
self.images.pop(-1)
else:
self.images = self.images + [self.images[0]]
self.images.pop(0)
#Reorder layers based on the fact that biggest images are in front
#Bring smallest images to front first
for s in sorted(self.subviews, key=lambda x: x.frame[3]): s.bring_to_front()

def touch_began(self, touch):
self.touch_direction = None

def touch_moved(self, touch):
if touch.location != touch.prev_location:
self.touch_direction = int(touch.location.x > touch.prev_location.x)
else:
pass

def touch_ended(self, touch):
if self.touch_direction != None:
ui.animate(self.anim, duration=0.25)

if __name__ == '__main__':
#Pick random images from default textures
import os, random
app_path = os.path.abspath(os.path.join(os.__file__, '../../../..'))
os.chdir(app_path + '/Textures')
imagenames = os.listdir(os.curdir)
validnames = []
for x in imagenames:
if not (x.startswith('ionicons') or x.startswith('Typicons')):
validnames.append(x)

images = [Image.open(random.choice(validnames)) for x in xrange(15)]
view = ui.View(background_color=BGCOLOR)
cf = CoverFlow(images)
view.add_subview(cf)
cf.present(hide_title_bar=1)
``````

`layout` literally removes all the subviews and recreates them, because I couldn't figure out how to adjust the frames easily, but the layout method takes under a hundredth of a second to perform so I don't think it's a problem.

• posted
1

Realized I can cut out most of `__init__`, gist is here. I think I'm done with it, now. I'd like to maybe get rid of the objects animating sliding behind, I'll edit the gist for that.

• posted
0

@Webmaster4o I would recommend making it a repo instead- as you can accept pull requests and make it easier to collaborate and build on.

• posted
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Sure. I've also just realized that the only thing (I think) preventing it from being 1.5-compatible is the assigning of arbitrary attributes to views (`sv.prev_frame`). I should be able to eliminate this easily, then it'll work on non-beta devices.

• posted
0

Having trouble setting alpha to 0 for the frame passing behind. I tried to set the frames alpha before and after animating, but this doesn't work because code after ui.animate is executed before the animation has finished. My code was this, but it's sloppy and doesn't work:
def animate(self):
len_subviews = len(self.subviews)

``````    for i, sub in enumerate(self.subviews):
next = self.subviews[(i + (1 if self.touch_direction else -1)) % len_subviews]
if next.prev_frame[0] < sub.prev_frame[0]:
resetter = sub
sub.alpha = 0

def anim():
#Change frames
for i, sub in enumerate(self.subviews):
next = self.subviews[(i + (1 if self.touch_direction else -1)) % len_subviews]
sub.frame = next.prev_frame

#Animate
ui.animate(anim, 0.25)
resetter.alpha = 1
#Re-sort self.images
if self.touch_direction:
self.images = [self.images[-1]]+self.images
self.images.pop(-1)
else:
self.images = self.images + [self.images[0]]
self.images.pop(0)

#Reorder layers based on the fact that biggest images are in front,
#Bring smallest images to front first
for s in sorted(self.subviews, key=lambda x: x.frame[3]): s.bring_to_front()

#Reassign prev_frame
for sub in self.subviews:
sub.prev_frame = sub.frame
``````

• posted
0

@Webmaster4o, I don't have much time to look at the forum at the moment. Many friends in town now. But your CoverFlow class is a great improvement.

• posted
1

Gist updated with backwards compatibility to 1.5, successful on my iPhone running ios7 and 1.5. I probably will end up making it a repo soon.

• Nice work! Coming along nicely. I am wondering if this could browse IOS photos? What would you use it for?

• posted
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Browsing iOS photos is a good idea.

• posted
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@TutorialDoctor, you ask what it could be used for. I think is just nice ui control, same as a slider. I think a nice step fwd would be to be able to provide a ui.view. Then not just images anymore. Also the cover controller doesn't care, just providing a series of frames with all the correct math and animations and touch events.

Internal error.

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