Pica

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A convenient image viewer. It can run as a standalone application or be used by other applications as an embedded viewer.

Main features

• Viewing individual channels with the same functionality as regular images.
• Automatic fitting of the window size to the image.
• Pinning the window on top of other windows.
• Area selection (pixels are taken directly from the image without any modifications).
• Customizable display of information, such as the name, format, resolution, or modification date.
• Useful context menu items, including a proper "Open with" menu.
• Supported formats: .png, .jpeg, .webp, .bmp, .gif, .ico, .avif, .heic, .heif, .tif.

Controls

Action	Hotkeys
Previous image or channel	A or ←
Next image or channel	D or →
Zoom	Mouse wheel
Slow zoom	Hold Shift, Ctrl, or Alt while zooming
Pan	Drag with LMB or MMB
Slow pan	Hold Shift or Alt while panning
Reset zoom and position	Space
Channel mode	Tab
Image filtering	F
Copy	Ctrl + C
Select area	Ctrl + drag with LMB
Select the entire image	Ctrl + A
Pan the image while an area selection is active	Drag with MMB
Switch between windowed and fullscreen modes	Double-click with LMB, if enabled in the settings
Close window or cancel	Esc

Quick start

Installation

Add the package:

dotnet add package Pica.Viewer

For a prerelease version, use --prerelease or specify the version number explicitly.

Theme

If the application does not yet use Fluent and SukiUI, add them to App.axaml:

<Application xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:suki="using:SukiUI"
             x:Class="Example.Desktop.App">
    <Application.Styles>
        <FluentTheme />
        <suki:SukiTheme ThemeColor="Blue" />
    </Application.Styles>
</Application>

Example

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;

using Pica.Protocol;
using Pica.Viewer;
using Pica.Viewer.Services;
using Pica.Viewer.Views;

ServiceCollection services = new();

services.AddLogging(builder =>
{
    builder.SetMinimumLevel(LogLevel.Warning);
});
services.AddPicaViewer();

ServiceProvider serviceProvider = services.BuildServiceProvider();

Guid imageId = Guid.NewGuid();
string imagePath = Path.GetFullPath("image.png");
string imageName = Path.GetFileName(imagePath);
PicaImageItem image = new(imageId, imagePath, imageName);
PicaViewerRequest request = new([image], imageId);

IImageViewerWindowFactory windowFactory = serviceProvider.GetRequiredService<IImageViewerWindowFactory>();
ImageViewerWindow window = await windowFactory.CreateAsync(request, CancellationToken.None);

window.Show();

window.Show() must be called on the UI thread.

Pica.Viewer forwards logs to the logging system already configured by the application and does not modify it.

Multiple images

Pass all images in PicaViewerRequest.Items, and the ID of the initially selected image in SelectedItemId:

PicaViewerRequest request = new(images, selectedImageId);

You can pass the path to a ready-made low-resolution image in PicaImageItem.PreviewFilePath for fast loading. If there is no preview image, this parameter can be omitted, but loading may take slightly longer.

Custom context menu items

Pass the list of items in PicaViewerRequest and their click handler in CreateAsync:

PicaActionDefinition[] actions =
[
    new(
        Id: "open-in-editor",
        DisplayName: "Open in editor",
        IconGeometry: "M13,3 L20,3 L20,10 L18,10 L18,6.4 L9.4,15 L8,13.6 L16.6,5 L13,5 Z M4,5 L10,5 L10,7 L6,7 L6,17 L16,17 L16,13 L18,13 L18,19 L4,19 Z",
        IconRotationDegrees: 0d,
        Targets: PicaActionTargets.CurrentImage | PicaActionTargets.Selection,
        Order: 0)
];
PicaViewerRequest request = new(images, selectedImageId, actions);
ImageViewerWindow window = await windowFactory.CreateAsync(request, actionDispatcher, CancellationToken.None);

actions is a list of PicaActionDefinition, and actionDispatcher is an implementation of IViewerActionDispatcher.

Pica calls DispatchCurrentImageAsync for the original image, DispatchSelectionAsync for the selected fragment, and DispatchDerivedImageAsync for the selected channel.

Example implementation of IViewerActionDispatcher:

public class ViewerActionDispatcher : IViewerActionDispatcher
{
    public Task DispatchCurrentImageAsync(
        PicaActionDefinition action,
        PicaImageItem item,
        CancellationToken ct)
    {
        return MyImageEditor.OpenAsync(item.FilePath, ct);
    }

    public Task DispatchSelectionAsync(
        PicaActionDefinition action,
        PicaImageItem item,
        byte[] pngContent,
        CancellationToken ct)
    {
        return MyImageEditor.OpenAsync(PicaImageFormats.SelectionFileName, pngContent, ct);
    }

    public Task DispatchDerivedImageAsync(
        PicaActionDefinition action,
        PicaImageItem item,
        string fileName,
        byte[] pngContent,
        CancellationToken ct)
    {
        return MyImageEditor.OpenAsync(fileName, pngContent, ct);
    }
}

MyImageEditor in the example is an application class that opens an image by path or from a byte array.