I want to position custom widgets on top of an image based on X and Y coordinates. Think of it as an overlay. Until now, I have tried a solution, where I used a Stack in a combination with Positioned, to position widgets above the image. The problem arises when I try this solution on different screen sizes. The overlaid widgets are off, depending on the screen size I'm testing on.
Here's my current implementation:
Expanded(
child: InteractiveViewer(
constrained: false,
minScale: 0.1,
maxScale: 2.0,
child: Stack(
children: [
Image.network(widget.plan.image),
Positioned(
bottom: 2927,
left: 6700,
child: SvgPicture.asset("assets/svg/pin.svg", height: 200)
)
],
)
),
)
Note that I'm also wrapping everything in InteractiveViewer because the Image I'm getting from the backend is very large.
EDIT: I have noted that for some reason the image dimensions are different on different displays. For example, photo dimensions on iPhone X are 10224x6526, where on iPhone 13 Pro Max image dimensions are 8192x5228. I am now investigating further why this is happening as this is probably the reason why custom widgets drawn on top are shifted on different screens.
EDIT 2: After a long research I've finally came across something. I own two physical devices - iPhone 12 and iPhone X. I was testing on simulator and something really odd happened; simulator is logging different image dimension simulating the same physical device - let me explain:
Original Image dimension coming from backend:
10224 × 6526
iPhone 12 simulator image dimension log after network call:
8192x5228
iPhone 12 PHYSICAL device image dimension log after network call:
10224 × 6526
iPhone X PHYSICAL device image dimension log after network call:
10224 × 6526
Which effectively means that something is working differently regarding the image scaling when using iOS simulator and physical device.
The best way to do this will be to try to position your items relative to the screen's width and height in percentage.
bottom: MediaQuery.of(context).size.height * 0.5 // 50% of the screen's height
left: MediaQuery.of(context).size.width * 0.3 // 30% of the screen's width
You are free to change the percentiles to suit you.
EDIT 2
x = (6700/width-of-photo) * 100
y = (2927/height-of-photo) * 100
With the issue concerning the size of the image, you might want to consider placing it inside a widget and giving it a max-height and max-width values.
Related
I am not interested in inside workings of logical pixels, I just want to know if flutter automatically use logical pixel
Container(
width:100,
child:...
)
Does flutter uses 100 pixel or logical pixel as width here, I can't figure it out.
You can print screen width
double kScreenWidth(BuildContext ctx) => MediaQuery.of(ctx).size.width;
you can see what it is like
Container(width: 100, ...)
logical pixels
So obvious,
What you see is what you got.
Flutter follows a simple density-based format like iOS. Assets might be 1.0x, 2.0x, 3.0x, or any other multiplier.
Flutter doesn’t have dps but there are logical pixels, which are basically the same as device-independent pixels. The so-called devicePixelRatio expresses the ratio of physical pixels in a single logical pixel.
from flutter dev doc
I used CachedNetworkImage widget in my code. Whenever i am calling it, the size of image is too large.
And when i tried to limit it's height to some les number, it's contents or some part of it are lost. I am unable to solve this problem. Here is screenshot of the image without any constraints -
I want only half of screen should be covered, while maintaining the width.And when i reduce it's height to 450, some part of it is gone, i mean it's lost(Check the photo, you will understand). Here's the picture with height 450 -
(I want only half of screen should be covered, while maintaining the width.)
(See, at top left corner of the main image in both pictures, and you will understand my problem).
Here's the code of the widget -
Widget cachedNetworkImage(mediaUrl, context) {
return CachedNetworkImage(
height: 380.0,
width: MediaQuery.of(context).size.width,
imageUrl: mediaUrl,
fit: BoxFit.cover,
placeholder: (context, url) => Padding(
child: CircularProgressIndicator(),
padding: EdgeInsets.all(20.0),
),
errorWidget: (context, url, error) => Icon(Icons.error_outline, color: Colors.red,),
);
}
Boxfit.cover will ensure the image fills the 'area' you want your image in, without distortion. Because the image itself has a different aspect ratio than the area you have defined, then part of it gets cropped. Given your image aspect ratio does not match your 'containers' aspect ratio you really only have two options if you want the 'container' completely filled, the image has to be cropped or stretched (distorted) in some way. See this for a complete view of BoxFit: https://api.flutter.dev/flutter/painting/BoxFit-class.html
The only other alternative is to ensure that your target container has the same aspect ratio as the image you want to put in it.
Update
The aspect ratio is just how wide the container is versus how high it is, like TV screens old and new 4x3 and 16x9. You can define a container who's size, or at least aspect ratio, matches the size of the image. You can then wrap it in FittedBox to have it fit the part of the screen it is meant to occupy, on all device sizes. These layout widgets need quite a lot of trial and error before you get the hang of them. Just keep trying different options.
I am coming to Flutter from a web background, where I am used to defining screen elements in terms of percentages of the height and width of the screen, or of elements that contain them.
I just completed a course.
Now that I am enthused and want to start building an app, I am a little confused, as the course only spoke of heights & widths in absolute pixel values. I can see this being problematic with different aspect rations, and especially with different orientations.
Is there a canonical approach to this? The official docs also seem to use absolute pixel values, so maybe I am missing a fundamental point.
A search suggests that I might use MediaQuery and then scale everything according to that. But, I don't see widespread use of that in code samples.
Is there a non-opinionated standard approach?
I am a little confused, as the course only spoke of heights & widths in absolute pixel values.
Actually, flutter uses density independent pixels (dp) for width/height arguments. dp actually scale with resolution, meaning 1 dp is displayed as the same PHYSICAL distance on every device. You don't have to worry about your elements being displayed at different sizes, just because the resolution of the screen they're on changes.
To be precise, flutter calls them logical pixel and:
By definition, there are roughly 38 logical pixels per centimeter, or about 96 logical pixels per inch, of the physical display.
So think about them as you would think about cm.
I am used to defining screen elements in terms of percentages of the height and width of the screen
Nonetheless, you might want to layout your widgets in a relative fashion (relative to the screen or the parent). For that purpose, flutter has different solutions:
Flexible
Expanded
Wrap
MediaQuery
LayoutBuilder
GridView
other layout options
Is there a non-opinionated standard approach?
It is a very opinionated question to begin with, but for example, Material design is a common standard for mobile-design. Flutters layout widgets are based around this approach.
But in the end, it is your design choice. For example, to achieve a responsive layout grid you could use Wrap, or you could use LayoutBuilder and determine yourself how you would like to layout rows and columns.
I would recommend you to scale widgets based on the size of the screen. This allows your application to be more flexible and adjust to various platforms and sizes such as large tablets or small phones. In order to do this, I recommend you to use the widget FractionallySizedBox which allows you to size widgets using a percentage of the screen size. For example, if you want a button widget to fill up 50 percent of a screen's width you can use the following code:
Container(
alignment: Alignment.center,
child: FractionallySizedBox(
widthFactor: 0.5,
child: FlatButton(
onTap: () {},
child: Text("PRESS HERE")
)
)
)
This code creates a button positioned in the center of the screen with a width of 50 percent of the screen size's width. You can also change the height of the button with the heightFactor field. By using this code the button widget will scale up and scale down for different screen sizes while still maintaining a size of half of the screen's width. For more resources, you should check out this video by the Flutter Team: https://youtu.be/PEsY654EGZ0 and their website on the FractionallySizedBox here: https://api.flutter.dev/flutter/widgets/FractionallySizedBox-class.html.
The FractionallySizedBox however is only one of many different approaches to making your flutter app fit to different screen sizes. Another approach is to use the AspectRatio Widget. Below is an example of this:
Container(
alignment: Alignment.center,
child: AspectRatio(
aspectRatio: 3/2
child: FlatButton(
onTap: () {},
child: Text("PRESS ME")
)
)
)
This code will create a button with a 3 to 2 ratio between its width and height. If the screen size changes the button will increase or decrease in size accordingly while again maintaining the 3 to 2 ratio. If you want more information the Flutter team also has a video on it (https://youtu.be/XcnP3_mO_Ms) along with some documentation here:(https://api.flutter.dev/flutter/widgets/AspectRatio-class.html).
Both widgets are perfectly fine and are considered standard practice to use but I personally use FractionallySizedBox more.
I hope my answer was helpful.
When I am using the MediaQuery to resize a container, like this =>
height: MediaQuery.of(context).size.height - 100,
the subtraction or the resizing of the container starts from the bottom instead of from the top. Please someone should help me out
You could wrap it with Align. It happens because naturally Flutter draw the Widgets from Top Left.
Something like this:
Align(
alignment: Alignment.bottomCenter,
child: Container(
height: MediaQuery.of(context).size.height - 100,
color: Colors.white,
),
),
As an addition to the answer by #FederickJonathan,
Align gives you some default positions to align your widget as described here: https://api.flutter.dev/flutter/painting/Alignment-class.html#constants
But you can also customize the position.
However you like, by giving Alignment as Alignment(X, Y).
X = -1.0 - 1.0, starting from left->right
Y = -1.0 - 1.0, starting from top->bottom
Fun fact:
Not Just flutter but almost all Rendering framework which paints the screen to display your views always starts from the Top-Left corner of the screen.
It is known as the origin point of the view/screen.
In flutter, if no co-ordinates or alignment is provided, then you'll see that the view is plotted starting from the top left corner.
The Origin point is also considered as the source of Light in material design. So all the shadows are cast to the bottom to the right side initially.
Update: Material Design combines various light sources for shadow. So the above fact is not true for material design but still you can see it in some other design guide lines.
in my Flutter application I am trying to get the real screen width (that can naturally be different on each device).
I am using MediaQuery.of(context).size.width but I've noticed that the values returned do not match the real screen resolution.
For instance,
On an simulator iPhone 11 Pro Max (that has resolution 2688 x 1242) I get MediaQuery.of(context).size.width= 414
On an emulator Nexus XL (that has resolution 1440 x 2560) I get MediaQuery.of(context).size.width = 411.42857142857144
On a real device iPhone 7 (that has resolution 1,334 x 750) I get MediaQuery.of(context).size.width = 375
Does anyone know why the value returned by MediaQuery differ from the real screen resolution in pixels?
Thanks
According to the size property's documentation :
The size of the media in logical pixels (e.g, the size of the screen).
Logical pixels are roughly the same visual size across devices.
Physical pixels are the size of the actual hardware pixels on the
device. The number of physical pixels per logical pixel is described
by the devicePixelRatio.
So you would do MediaQuery.of(context).size.width * MediaQuery.of(context).devicePixelRatioto get the width in physical pixels.