glCopyTexSubImage1D

glCopyTexSubImage1D: man3/glCopyTexSubImage1D.xml

glCopyTexSubImage1D replaces a portion of a one-dimensional texture image with pixels from the current GL_READ_BUFFER (rather than from main memory, as is the case for glTexSubImage1D ). The screen-aligned pixel row with left corner at ( x, y ), and with length width replaces the portion of the texture array with x indices xoffset through xoffset + width - 1, inclusive. The destination in the texture array may not include any texels outside the texture array as it was originally specified. The pixels in the row are processed exactly as if glReadPixels had been called, but the process stops just before final conversion. At this point, all pixel component values are clamped to the range 0 1 and then converted to the texture's internal format for storage in the texel array. It is not an error to specify a subtexture with zero width, but such a specification has no effect. If any of the pixels within the specified row of the current GL_READ_BUFFER are outside the read window associated with the current rendering context, then the values obtained for those pixels are undefined. No change is made to the or parameters of the specified texture array or to texel values outside the specified subregion.

The glPixelStore mode affects texture images.