glColorMask() question

Hi, I have one problem.
In description of void glClear(GLbitfield mask); I have read this “Masking operations, such as glColorMask() and glIndexMask(), are also effective”. So I do this:

glClearColor(0,0,0,0.5); // unsigned byte (0,0,0,127) right?
glCopyTexImage2D(GL_TEXTURE_2D,0,GL_RGBA,0,0,WindowWidth,WindowHeight,0); // my window is 1024x768
glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA, GL_UNSIGNED_BYTE, pTextureData); // its rectangular texture, same resolution 1024x768, belive me :)

And then I try to look alpha component, for example, pTextureData[3] its not equal to 127. Help me plz?

if it’s not 127, then what is it?

does your pixelformat have alphaBits?

Do not crosspost please. There are answers in the advanced forum.