framebuffer color problem in a1200

[serverclient2004]

i open /dev/fb0, and mmap the 18bpp framebuffer successfully, but when i display a 16bpp picture(i have carefully changed the pixel format into 18 bpp), things changed.

it seems that some of the color values doesn't exist, when i write color value into the framebuffer mapped array, a1200 screen only display
black color.

what shall i do ? does it has any relationship with the settings of fb_cmap ?
if so how can i set it correctly ?

great thanks for any advices.

[serverclient2004]

the framebuffer info in a1200 looks like this :
open /dev/fb0 successfully !
framebuffer fixed info --->

cardid :
smemstart : 0x5c001000
smemlen ; 0x72000
type ; 0
visual : 2
line_len : 720
framebuffer var info --->

xres : 240
yres : 320
xres_virtual : 240
yres_virtual : 644
xoffset : 0
yoffset : 0
bpp : 18
width : -1
height : -1
color start : daadc93
color length : 40000614

i also test on real linux, outputs looks like yres == yres_virtual.
what's does the yres_virtual used for ? sorry for my limited knowledge
in framebuffer operate.

line_len : 720

means 240x3, screen width 240, 3 bytes per pixel. i have checked that
the 18bpp format in a1200 is 6x6x6 just like 24bpp 8x8x8, different is
sys would dismiss the high 2 bits of color value.

[serverclient2004]

can any one send me a framebuffer sample in a1200 to display a picture ?

thank you very much.

i have tried for few days, still no further step.

[serverclient2004]

cheers, i have solved that problem, seems that i always use a wrong method.

i googled for 18 bpp, lots of infomation show me that 18 bpp may worked
like 24 bpp, uses byte align, the pixel format should be :
00rrrrrr 00gggggg 00bbbbbb
that would be faster in color depth convert oprations.

but after long time test in real a1200 hardware, i found that the fact is
not as i thought. the 18 bpps pixel format that a1200 really use is packed
6x6x6，not byte align 6x6x6.
000000rr rrrrgggg ggbbbbbb

it waste much of my time, but finally i solved it.
i paste it here, hope to save other developers' time.