Blazorise Cropper component

A component used to crop images.

When building an application, best practice requires reducing an image's surrounding noise and directing a user's attention to a specific part of the image. Image cropping is a method for manipulating images to remove any unwanted elements. By changing the aspect ratio or orientation, we can draw viewers' eyes to the photograph's primary subject and improve the overall composition. This applies to profile pictures or uploading images with specific dimensions.

The new Cropper component handles all of that. You can upload an image and then select part of it, rotate, scale, and crop it. You can also add a preview by adding a CropperViewer whenever on a page, and it will automatically synchronize with the latest selection.

Installation

NuGet

Install extension from NuGet. 
Install-Package Blazorise.Cropper

Imports

In your main _Imports.razor add: 
@using Blazorise.Cropper

Message Size

This step is recommended for Blazor Server only. In a default Blazor Server project template, the SignalR settings might be too small for some components like Cropper. To make it work, you should increase the MaximumReceiveMessageSize in your projects Startup.cs. 
.AddHubOptions(o =>
{
    o.MaximumReceiveMessageSize = 1024 * 1024 * 100;
})

Examples

Basic

The image cropper is pretty straightforward. You need to define a Source parameter, and a reference. 
<Row>
    <Column>
        <FieldLabel>
            Image Cropper
        </FieldLabel>
        <FieldBody>
            <Cropper @ref="cropper" Source="img/gallery/6.jpg" SelectionChanged="@OnSelectionChanged" Style="aspect-ratio: 16 / 9; height: 100%;" />
        </FieldBody>
    </Column>
    <Column>
        <Div Margin="Margin.Is2.FromBottom">
            <Button Color="Color.Primary" Clicked="@GetCroppedImage" Disabled="@cropButtonDisabled">Get Cropped Image</Button>
            <Button Color="Color.Secondary" Clicked="@ResetSelection" Disabled="@cropButtonDisabled">Reset Selection</Button>
        </Div>
        <Image Source="@result" Border="Border.Is1" Style="width: 250px; height: 250px;" />
    </Column>
</Row>

@code {
    private Cropper cropper;
    private string result;
    private bool cropButtonDisabled = true;

    private Task OnSelectionChanged( CropperSelectionChangedEventArgs eventArgs )
    {
        if ( eventArgs.Width != 0 )
        {
            cropButtonDisabled = false;

            return InvokeAsync( StateHasChanged );
        }

        return Task.CompletedTask;
    }

    private async Task GetCroppedImage()
    {
        result = await cropper.CropAsBase64ImageAsync( new() { Width = 250, Height = 250 } );
    }

    private async Task ResetSelection()
    {
        cropButtonDisabled = true;

        await cropper.ResetSelection();
    }
}

Viewer

To add a preview support you can use a <CropperViewer> component. Once added you need to connect it to a <Cropper> by assigning the CropperState parameter. This parameter is used as a synchronization context bewteen the cropper and a viewer. 
<Row>
    <Column>
        <FieldLabel>
            Image Cropper
        </FieldLabel>
        <FieldBody>
            <Cropper Source="img/gallery/3.jpg" CropperState="@cropperState" />
        </FieldBody>
    </Column>
    <Column>
        <FieldLabel>
            Preview
        </FieldLabel>
        <FieldBody>
            <CropperViewer CropperState="@cropperState" Margin="Margin.Is2.FromBottom" Style="width: 150px; height: 150px;" />
            <CropperViewer CropperState="@cropperState" Margin="Margin.Is2.FromBottom" Style="width: 100px; height: 100px;" />
            <CropperViewer CropperState="@cropperState" Margin="Margin.Is2.FromBottom" Style="width: 50px; height: 50px;" />
        </FieldBody>
    </Column>
</Row>

@code {
    private CropperState cropperState = new();
}

API

Attributes

Cropper

Name Description Type Default
Ratio Defines the aspect ratio of the image cropper. CropperAspectRatio Is1x1
Source The original image source. string null
Alt The alt text of the image. string null
CropStarted This event fires when the canvas (image wrapper) or the crop box starts to change. EventCallback
CropMoved This event fires when the canvas (image wrapper) or the crop box is changing. EventCallback
CropEnded This event fires when the canvas (image wrapper) or the crop box stops changing. EventCallback
Cropped This event fires when the canvas (image wrapper) or the crop box changes. EventCallback
Zoomed This event fires when a cropper instance starts to zoom in or zoom out its canvas (image wrapper). EventCallback
Enabled Is the cropper enabled. bool true
CropperState Provides a shared state and syncronization context between the cropper and cropper viewer. CropperState null
CrossOrigin The cross-origin attribute of the image. string null
ImageReady This event fires when the image is ready / loaded. Func<Task> null

CropperViewer

Name Description Type Default
CropperState Provides a shared state and syncronization context between the cropper and cropper viewer. CropperState

CropperCropOptions

Name Description Type Default
Width The destination width of the output canvas. int 0
Height The destination height of the output canvas. int 0
ImageType A string indicating the image format. The default type is image/png this image format will be also used if the specified type is not supported. string image/png
ImageQuality A Number between 0 and 1 indicating the image quality to be used when creating images using file formats that support lossy compression (such as image/jpeg or image/webp). double? 1.0
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