Why doesn't the parent container display scrollbars when the Canvas width overflows?

FAQs and solutions for Canvas canvas overflowing the parent container and scroll bars do not display

When drawing with Canvas, you often encounter a layout problem: the parent container has overflow: auto , and the scroll bar is displayed when the expected content exceeds the expected content, but the actual effect does not match the expected one. For example, when the width of the Canvas exceeds the parent container, the parent container will be expanded, and when the height exceeds the parent container, the scroll bar can be displayed normally. This article will conduct in-depth analysis of this issue and provide solutions.

Problem description:

A parent container sets width: 100% , height: 100% and overflow: auto attributes. The setDimensions method of Fabric.js is used internally to set the width and height of Canvas. When the Canvas height exceeds the parent container height, the vertical scroll bar is displayed normally; but when the Canvas width exceeds the parent container width, the parent container width will be extended, but the horizontal scroll bar will not appear. why is that?

Problem analysis and solutions:

The core of the problem is that the parent container width uses 100% of the percentage. width: 100% means that the parent container width will be adaptively adjusted according to its content (Canvas). When the Canvas width exceeds the expected width of the parent container, the parent container automatically expands the width to accommodate the Canvas, so there is no horizontal scroll bar.

Solution:

1. Set fixed width: Set a fixed width value for the parent container (for example width: 800px ). In this way, when the Canvas width exceeds this fixed value, the parent container displays a horizontal scroll bar according to overflow: auto attribute.

2. Use viewport width: Use width: 100vw . This way, the parent container width will always be consistent with the browser viewport width, ensuring that horizontal scroll bars can appear when the Canvas width exceeds the viewport width.

In short, the parent container must have a clear width that will not change dynamically according to the content in order to correctly achieve horizontal overflow scrolling. Only when the width of the parent container is fixed and the Canvas width exceeds this fixed width, overflow: auto can effectively display the horizontal scroll bar.

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