Eric Chu

Alpha test on iMX6Q

Discussion created by Eric Chu Employee on Sep 12, 2012
Latest reply on Mar 25, 2013 by Eric Beaudoin

There are some test cases used to show alpha effect in previous unit_tests, but it is not found in latest Linux BSP release. So I prepare a simple test code to perform colorkey, global alpha, local alpha or alpha in pixel option for video combining, it could be useful when customer wants to see the effect.

I have checked test code on MX6Q ARM2 board and Linux release package is L3.0.15_12.05.01_ER_source.tar.gz.

Test based on the following assumptions:

1. Video combining is performed by the DP, BG video --> /dev/fb0, FG UI --> /dev/fb1

2. Panel resolution is 1024x768


Here are test steps:

1. Play a video or a picture on /dev/fb0.

2. Use fb_setup to setup fb1.


It will fill pixel value in frame buffer and alpha value in alpha buffer as below.

Frame buffer in RGBA mode:

for (i = 0; i < fb_var.yres; i++)


     for (j = 0; j < fb_var.xres; j++)


          if (i < fb_var.yres / 4)

               pbuf[i * screen_width + j] = 0xFF000080;       //Red pixel with alpha value 0x80 in first region

          else if (i < fb_var.yres / 2)

               pbuf[i * screen_width + j] = 0x00FF00FF;       //Green pixel opaque in second region

          else if (i < fb_var.yres * 3 / 4)

               pbuf[i * screen_width + j] = 0x0000FF00;       //Blue pixel transparent in third region


               pbuf[i * screen_width + j] = 0xFFFFFFFF;     //White pixel opaque in fourth region



Alpha buffer:


     memset(alpbuf, 0xFF, alp_size/4);                          //Alpha value is 0xFF in first region

     memset(alpbuf+alp_size/4, 0xAA, alp_size/4);         //Alpha value is 0xAA in second region

     memset(alpbuf+alp_size/2, 0x80, alp_size/4);          //Alpha value is 0x80 in third region

     memset(alpbuf+alp_size*3/4, 0x55, alp_size/4);       //Alpha value is 0x55 in fourth region


3. Use alpha_test to check colorkey, global alpha, local alpha and alpha in pixel effect.

colorkey on:      ./alpha_test colorkey_on <colorkey value>     //colorkey value, such as 0xFF0000 for red

colorkey off:      ./alpha_test colorkey_off

global alpha:     ./alpha_test alpha_global <alpha value>          //alpha value, such as 0x80

local alpha:      ./alpha_test alpha_local         //alpha effect is accordant with alpha buffer set in step 2

alpha in pixel:  ./alpha_test alpha_pixel         //alpha effect is accordant with alpha value in pixel set in step 2

alpha off:         ./alpha_test alpha_off

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