fix(toolbox): use current device pixel ratio by default for exporting crisp and clear images.

[plainheart]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Currently, we are using the default value 1 as the DPR instead of the real device pixel ratio of the user, which will make the exported image blurred in retina devices. To get a clear one, the user has to set the option as follows:

toolbox: {
    feature: {
        saveAsImage: {
            pixelRatio: 2.5 // specific dpr
        }
    }
}

This PR is intended to enable users to export a clearer image without any specific option.

Details

Before: What was the problem?

By default, the exported image is blurred in retina devices.

After: How is it fixed in this PR?

Don't specify the default pixelRatio as 1. Use the ECharts#getDevicePixelRatio() method to get the real dpr instead.

Usage

Are there any API changes?

• The API has been changed.

Related test cases or examples to use the new APIs

Please refer to test/toolbox-title.html or any other case related to the toolbox.

Others

Merging options

• Please squash the commits into a single one when merge.

Other information

[echarts-bot]

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[echarts-bot]

Congratulations! Your PR has been merged. Thanks for your contribution! 👍