add option to set image heigth and with to null

[The-Redhat]

With the new ImageProperties it isn't possible to set width & height to null. Because the given height an width of the html is often optimized for large displays, empty areas are showing up.

In my opinion the version 0.10.1 should be marked as breaking, because it introduces some visual changes.

[The-Redhat]

For example when the html uses srcset the height and width attributes aren't ment to be used on phones. The height is often set to 1920x1080 which leads to whitespace in flutter_html.

[Sub6Resources]

Yeah, there are a couple issues with the new way we handle images. I'll take a look at it and add a way to set width and height to null.

[andreyeurope]

@The-Redhat Could you explain the issue in detail? I don't get what you mean by set image heigth and width to null. If you don't set the ImageProperties width and height, or have width and height attributes in html, the width and height from the Image widget will be set to null.

[The-Redhat]

@andreyeurope When you have width and height attributes in your html the Image Widgres is set to these attributes. But for example when you have a srcset the height an width attributes doesn't represent the actual height an width of the picture. This leads to empty spaces. In this example the library should ignore the specified height and width attributes.

[andreyeurope]

Do you have an example with screenshots?

[The-Redhat]

Sure, but I'm currently on vacation. I can post an example with screenshot in two days.

[andreyeurope]

Ok, cool. Looking forward to it. Enjoy your holiday.

[The-Redhat]

Nevermind found one on my phone:

<img class="alignnone wp-image-2210 size-full" src="https://pelikan-sz.de/wp-content/uploads/2019/04/clevershuttle-screenshot.jpg" alt="Screenshots der App von CleverShuttle" width="1920" height="1026" srcset="https://pelikan-sz.de/wp-content/uploads/2019/04/clevershuttle-screenshot.jpg 1920w, https://pelikan-sz.de/wp-content/uploads/2019/04/clevershuttle-screenshot-300x160.jpg 300w, https://pelikan-sz.de/wp-content/uploads/2019/04/clevershuttle-screenshot-768x410.jpg 768w, https://pelikan-sz.de/wp-content/uploads/2019/04/clevershuttle-screenshot-1024x547.jpg 1024w, https://pelikan-sz.de/wp-content/uploads/2019/04/clevershuttle-screenshot-650x347.jpg 650w" sizes="(max-width: 1920px) 100vw, 1920px" />

[andreyeurope]

I gave it a thought over the weekend, and I was thinking to add a flag (or two) to ignore the width and height values found in the HTML img element.
@Sub6Resources Did you think about a solution for this edge case?

[The-Redhat]

An other option would be to set the default for height width to below zero and filter out values below zero when creating the Image Widget. This would simplify it and makes it a non-breaking change Otherwise you have a lot of flags.

[Sub6Resources]

@andreyeurope I think @The-Redhat's suggestion of using negative values for width/height in the ImageProperties object will be the best way to go so we can keep the change non-breaking.

[sooxt98]

Thanks , I'll try it later

[sooxt98]

@Sub6Resources this need a documentation for this, If not beginners need to look into the code

[Sub6Resources]

@sooxiaotong Yup, the documentation does need to be improved both for this and all the other properties as well. I've opened a new issue for documentation: #159.