UEFI News and Commentary

Sunday, January 31, 2010

UEFI HII (Part 10): Images

Before starting, you should be aware that the term 'image' has two different meanings in UEFI. First, it refers to executables (EXE), such as drivers and applications, that get loaded into memory by the LoadImage() and StartImage() services. Second, it refers to rectangular, full-color images.

Support for these images started with the UEFI 2.0 specification, with the EFI_GRAPHICS_OUTPUT_PROTOCOL. This protocol provide device-independent services for moving bitmapped images back and forth from a video device. But, it provided no standard means for finding and managing these images.

Then the UEFI 2.1 specification introduced the HII Database. Each driver can install pre-packaged images into the database. Then the driver can manipulate or display them using the EFI_HII_IMAGE_PROTOCOL.

Image Attributes
Images have the following attributes:
  • Identifier. Along with the database handle, this identifier uniquely specifies the image.
  • Width. The number of pixels per image row.
  • Height. The number of image rows.
  • Transparent. Indicates whether the pure black pixels (RGB(0,0,0)) will be drawn transparently over the background.
  • Bitmap. Image pixels are organized left-to-right and then top-to-bottom. Each image pixel consists of 32-bits. The first 8-bits in each pixel are the blue (0 = off, 255 = on), the next 8-bits are the green and the next 8-bits are the blue.

Image Services
The UEFI HII Image protocol provides two classes of services:  

  1. Get/Set. You can get an image from the HII database, change an image in the HII database and add a new image to the HII database.

  2. Draw. You can draw an image, either using an image identifier or from a raw bitmapped image. In both cases, the drawing can be done directly to the screen or into another image, with or without clipping.

Images are slowly being integrated into firmware as an integral part, simply because of user expectations and a desire for OEMs to stand out in a crowd. UEFI 2.1 provides built-in support for basic image manipulation services. UEFI 2.3 also added support for animations. In our next article, we will look at how UEFI stores different types of images in the HII packages.

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