What is the difference between reflow and redraw?

The difference between reflow and redraw is: 1. Reflow is triggered when the DOM structure changes, while redrawing is triggered when the style attribute of the element changes; 2. Reflow needs to recalculate the position of the element. and size, while redrawing only requires redrawing the element's style; 3. Reflow will cause redrawing, but redrawing does not necessarily cause reflow.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

Reflow and redrawing are two important concepts in the web page rendering process. They play an important role in performance optimization and web page development. Reflow refers to the process in which the browser calculates the position and size of elements based on the DOM structure and CSS style, and draws them on the screen. Repaint refers to the process in which the browser draws based on the style attributes of the element. Although reflow and redraw are closely related in the rendering process, there are some clear differences between them.

First of all, the trigger conditions for reflow and redraw are different. Reflow is triggered when the DOM structure changes, such as adding, deleting or modifying elements, modifying the position or size of elements, etc. Redrawing is triggered when the element's style attributes change, such as modifying the element's color, background, border, etc.

Secondly, the cost of reflow is higher than redrawing. Reflow is expensive because it requires recalculating the position and size of elements. Redrawing only requires redrawing the style of the element, so the cost is relatively low. Therefore, in performance optimization, we should try to reduce the number of reflows to improve the rendering performance of the web page.

In addition, reflow will cause redrawing, but redrawing does not necessarily cause reflow. When the style attributes of an element change, the browser will first redraw, then recalculate the position and size of the element based on the new style attributes, and if necessary, trigger reflow of other elements. Therefore, reflow is a necessary condition for redrawing, but redrawing does not necessarily cause reflow.

In order to reduce reflow and redraw, we can take some optimization measures. First of all, we should try to avoid frequently modifying the style attributes of elements. We can merge multiple modifications into one, or use CSS animation to achieve dynamic effects. Secondly, we can use document fragments (DocumentFragment) to insert or delete elements in batches to reduce the number of reflows. In addition, we can also use CSS3 hardware acceleration (hardware acceleration) to improve the rendering performance of web pages.

In short, reflow and redrawing are two important concepts in the web page rendering process. They play a vital role in performance optimization and web page development. Understanding the difference between reflow and redrawing and taking corresponding optimization measures can improve the rendering performance of web pages and enhance the user experience. .

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