[feature-request]: Allow background-image with gradients

[GregOnNet]

Hello @tjoskar,

thank you for providing this neat library. Currently, I try to do something like this:

TEMPLATE

  <div [lazyload]="backgroundImageWithGradient"></div>

COMPONENT

@Component({ ... })
export class SomeComponent {
  imageUrl
  backgroundImageWithGradient = `linear-gradient(rgba(0,0,0,0.45), rgba(0,0,0,0.7)), url(' + this.imageUrl + ')`;
}

Of course, this fails, since [lazyload] expects an image URL. It would help me if I could do something like shown above in order to define a gradient on top of the loaded image.

What do you think about it?

[tjoskar]

Hi @GregOnNet,

This is a great idea. I see a few different options here:

1. Check wherever lazyload is a URL or CSS-style and act accordingly. I do, however, think this will be hard and probably introduce bugs.
2. Introduce a new flag that is telling that the string is CSS, something like: <div [lazyload]="backgroundImageWithGradient" resourceType="css"></div>. But i'm not sure about that.
3. Use a custom hook (this should be possible today):

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { LazyLoadImageModule, IntersectionObserverHooks, Attributes, LAZYLOAD_IMAGE_HOOKS } from 'ng-lazyload-image';
import { AppComponent } from './app.component';

export class LazyLoadImageHooks extends IntersectionObserverHooks {
  setLoadedImage(att: Attributes) {
    if (att.element.dataset.backgroundWithGradient) {
      att.element.style.backgroundImage = att.element.dataset.backgroundWithGradient;
    } else {
      super.setLoadedImage(att);
    }
  }
}

@NgModule({
  declarations: [AppComponent],
  imports: [BrowserModule, LazyLoadImageModule],
  providers: [{ provide: LAZYLOAD_IMAGE_HOOKS, useClass: LazyLoadImageHooks }],
  bootstrap: [AppComponent],
})
export class MyAppModule {}

And then using the following template: <div [lazyload]="imageUrl" [attr.data-background-with-gradient]="backgroundImageWithGradient"></div>

I do however think this should be supported out of the box but I'm not sure how. There is an old, open, PR where we have discussed similar issues.

[GregOnNet]

Hi,

thanks for the hint. I will try the hook.

Concerning the API. I agree it would be nice to have this feature out-of-the-box. Maybe it could be delivered as a separate Directive:

<div [lazyBackground]="imageUrl" [lazyBackroundGradient]="{
  position: "below"|"above",
  definition: "linear-gradient(rgba(0,0,0,0.45), rgba(0,0,0,0.7))"
}">

[tjoskar]

I think it will be hard to implement this so it scales. What if I want to add no-repeat after the image url, like:

background: linear-gradient(rgba(0, 0, 0, 0), rgba(0, 0, 0, 1)), url('...') no-repeat;

And I believe it exists more edge cases. Maybe we can use a template, something like this:

<div [lazyBackground]="imageUrl" [styleToApply]="linear-gradient(rgba(0,0,0,0.45), rgba(0,0,0,0.7)), url('$IMAGE_URL$')">

But should that style also be used for the default/error-image?