glTextureSubImage2D

glTexSubImage2D: man4/glTexSubImage2D.xml

Texturing maps a portion of a specified texture image onto each graphical primitive for which texturing is enabled. glTexSubImage2D and glTextureSubImage2D redefine a contiguous subregion of an existing two-dimensional or one-dimensional array texture image. The texels referenced by pixels replace the portion of the existing texture array with x indices xoffset and xoffset + width - 1, inclusive, and y indices yoffset and yoffset + height - 1, inclusive. This region may not include any texels outside the range of the texture array as it was originally specified. It is not an error to specify a subtexture with zero width or height, but such a specification has no effect. If a non-zero named buffer object is bound to the GL_PIXEL_UNPACK_BUFFER target (see glBindBuffer ) while a texture image is specified, pixels is treated as a byte offset into the buffer object's data store.

glPixelStore modes affect texture images. glTexSubImage2D and glTextureSubImage3D specify a two-dimensional subtexture for the current texture unit, specified with glActiveTexture. GL_STENCIL_INDEX is accepted for format only if the GL version is 4.4 or higher.