Frame buffer

Frame Buffer: Referred to as frame buffer or video memory, it is a direct image of the picture displayed on the screen, also known as a bit map or raster. Each storage unit of the frame buffer corresponds to a pixel on the screen, and the entire frame buffer corresponds to a frame of image.

A window (ie frame buffer) that supports OpenGL rendering may contain the following combinations:

· Up to 4 color buffers

 A depth buffer ,A template cache ,An accumulation cache ,A multi-sample buffer

The frame buffer is an interface provided by Linux for display devices. It is a device after the video memory is abstracted. It allows upper-level applications to directly read and write the display buffer in graphics mode. This operation is abstract and unified. The user does not need to care about the location of the physical video memory, the paging mechanism, etc. specific details. These are all done by the Framebuffer device driver.

Linux FrameBuffer essentially only provides a hardware abstraction for graphics devices. In the eyes of developers, FrameBuffer is a display buffer, and writing data in a specific format to the display buffer means outputting content to the screen. So FrameBuffer is a whiteboard. For example, for the FrameBuffer initialized to 16-bit color, the two bytes in the FrameBuffer represent a point on the screen, from top to bottom, from left to right, the screen position and the memory address have a linear relationship in order.

The frame buffer can be anywhere in the system memory , and the video controller refreshes the screen by accessing the frame buffer. The frame buffer is also called refresh buffer or refresh buffer, where the frame refers to the entire screen area.

The frame buffer has an address, which is in memory. By continuously writing data to the frame buffer, the display controller automatically fetches the data from the frame buffer and displays it. All graphics share the same frame buffer in memory.

When the CPU specifies the display controller to work, the display controller will go to the designated place to fetch data and instructions according to the control of the CPU. The current data is generally fetched from the video memory. If the video memory cannot be stored, it will be fetched from the memory and the memory is also If it is not enough, it is taken from the hard disk. Of course, it is not stored in the internal storage, but to save memory, it can be placed in the hard disk, and then the display controller can be controlled by instructions to take it.