internals.rst 2.7 KB

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  1. =============================
  2. Frame Buffer device internals
  3. =============================
  4. This is a first start for some documentation about frame buffer device
  5. internals.
  6. Authors:
  7. - Geert Uytterhoeven <geert@linux-m68k.org>, 21 July 1998
  8. - James Simmons <jsimmons@user.sf.net>, Nov 26 2002
  9. --------------------------------------------------------------------------------
  10. Structures used by the frame buffer device API
  11. ==============================================
  12. The following structures play a role in the game of frame buffer devices. They
  13. are defined in <linux/fb.h>.
  14. 1. Outside the kernel (user space)
  15. - struct fb_fix_screeninfo
  16. Device independent unchangeable information about a frame buffer device and
  17. a specific video mode. This can be obtained using the FBIOGET_FSCREENINFO
  18. ioctl.
  19. - struct fb_var_screeninfo
  20. Device independent changeable information about a frame buffer device and a
  21. specific video mode. This can be obtained using the FBIOGET_VSCREENINFO
  22. ioctl, and updated with the FBIOPUT_VSCREENINFO ioctl. If you want to pan
  23. the screen only, you can use the FBIOPAN_DISPLAY ioctl.
  24. - struct fb_cmap
  25. Device independent colormap information. You can get and set the colormap
  26. using the FBIOGETCMAP and FBIOPUTCMAP ioctls.
  27. 2. Inside the kernel
  28. - struct fb_info
  29. Generic information, API and low level information about a specific frame
  30. buffer device instance (slot number, board address, ...).
  31. - struct `par`
  32. Device dependent information that uniquely defines the video mode for this
  33. particular piece of hardware.
  34. Visuals used by the frame buffer device API
  35. ===========================================
  36. Monochrome (FB_VISUAL_MONO01 and FB_VISUAL_MONO10)
  37. --------------------------------------------------
  38. Each pixel is either black or white.
  39. Pseudo color (FB_VISUAL_PSEUDOCOLOR and FB_VISUAL_STATIC_PSEUDOCOLOR)
  40. ---------------------------------------------------------------------
  41. The whole pixel value is fed through a programmable lookup table that has one
  42. color (including red, green, and blue intensities) for each possible pixel
  43. value, and that color is displayed.
  44. True color (FB_VISUAL_TRUECOLOR)
  45. --------------------------------
  46. The pixel value is broken up into red, green, and blue fields.
  47. Direct color (FB_VISUAL_DIRECTCOLOR)
  48. ------------------------------------
  49. The pixel value is broken up into red, green, and blue fields, each of which
  50. are looked up in separate red, green, and blue lookup tables.
  51. Grayscale displays
  52. ------------------
  53. Grayscale and static grayscale are special variants of pseudo color and static
  54. pseudo color, where the red, green and blue components are always equal to
  55. each other.