How to Resize Images for Free Pascal's Multi-Resolution ImageList

When designing a high-DPI aware application using Free Pascal, it's essential to consider image resolution and scaling. This is particularly important when working with multi-resolution images in your LCL application. In this article, we'll explore how to resize images for Free Pascal's multi-resolution ImageList.

Understanding Multi-Resolution Images

A multi-resolution image is one that is designed to be displayed at different resolutions, such as 96ppi (100% scale) and higher. To create a multi-resolution image, you need to specify the different image sizes required by your application.

Adding Sliced or Scaled Images to an ImageList

To add sliced or scaled images to an ImageList in Free Pascal, you can use the AddSliced or AddSlice method. The AddSliced method is used when adding multiple icons from a single image, while AddSlice is used when adding a custom rect from a single image.

Changes Affecting Backwards Compatibility

With the introduction of multi-resolution images in Lazarus 1.9, some changes were made to the TImageList component. The SetScaled property was added, which allows you to set the scaled image in your High-DPI aware LCL application. This change affects backwards compatibility, as older versions of Lazarus did not support multi-resolution images.

Creating a Multi-Resolution ImageList

To create a multi-resolution ImageList in your Free Pascal application, you need to decide on the basic image size, usually 16x16 pixels. You then need to specify the different image sizes required by your application using the AddSliced or AddSlice method.

Lazarus 1.9 and Newer

In Lazarus 1.9 and newer versions, the TImageList component has been rewritten to support multiple resolutions of one image. This means that you can create a single image with different resolutions, and then add it to an ImageList using the AddSliced or AddSlice method.

Lazarus 1.8 and Older

If you're working with Lazarus 1.8 or older versions, there are two high-DPI alternatives you can use: resize all images in TImageList, or use a third-party library that supports multi-resolution images.

In conclusion, resizing images for Free Pascal's multi-resolution ImageList is an essential step in creating high-DPI aware applications. By following the steps outlined above, you can create a multi-resolution image and add it to an ImageList using the AddSliced or AddSlice method.

Free pascal resize image