Texturing - Praise for OpenGL ES 30 Programming Guide - page 271

GL_R8I , GL_R8UI , GL_R16I , GL_R16UI , GL_R32I ,
GL_R32UI , GL_RG8I , GL_RG8UI , GL_RG16I ,
GL_RG16UI , GL_RG32I , GL_RG32UI , GL_RGBA8I ,
GL_RGBA8UI , GL_RGB10_A2UI , GL_RGBA16I ,
GL_RGBA16UI , GL_RGBA32I , or GL_RGBA32UI

x the x window-coordinate of the lower-left rectangle

in the framebuffer to read from

the y window-coordinate of the lower-left rectangle
in the framebuffer to read from

y

the width in pixels of the region to read

width

the height in pixels of the region to read

height

borders are not supported in OpenGL ES 3.0, so this
parameter must be 0

border

Calling this function will cause the texture image to be loaded with the
pixels in the color buffer from region ( x , y ) to ( x + width - 1, y + height - 1).
This width and height of the texture image will be the size of the region
copied from the color buffer. You should use this information to fill the
entire contents of the texture.

In addition, you can update just the subregion of an already-specified
image using glCopyTexSubImage2D .

void glCopyTexSubImage2D (GLenum target,
GLint level , GLint xoffset ,
GLint yoffset , GLint x , GLint y ,
GLsizei width , GLsizei height )

specifies the texture target, either GL_TEXTURE_2D or one of
the cubemap face targets
(GL_TEXTURE_CUBE_MAP_POSITIVE_X ,
GL_TEXTURE_CUBE_MAP_NEGATIVE_X, and so on )

target

specifies which mip level to update

level

the x index of the texel to start updating from

xoffset

the y index of the texel to start updating from

yoffset

the x window-coordinate of the lower-left rectangle in the
framebuffer to read from

x

the y window-coordinate of the lower-left rectangle in the
framebuffer to read from

y

(continues)