Creating a texture may be more computationally expensive than modifying an
existing one.
In OpenGL there are routines to replace all or
part of a texture image with new information.
This can be helpful for certain applications, such as using real-time, captured video images as texture images. For that application, it makes sense to create a single texture and use glTexSubImage2D() to repeatedly replace the texture data with new video images. Also, there are no size restrictions for glTexSubImage2D() that force the height or width to be a power of two. This is helpful for processing video images, which generally do not have sizes that are powers of two.
void glTexSubImage2D( GLenum target, GLint level,
GLint xoffset, GLint yoffset,
GLsizei width, GLsizei height,
GLenum format, GLenum type,
const GLvoid *pixels );
Defines a two-dimensional texture image that replaces all or part of a contiguous subregion (in 2D, it's simply a rectangle) of the current, existing two-dimensional texture image. The target parameter must be set to GL_TEXTURE_2D.
The level, format, and type parameters are similar to the ones used for glTexImage2D(). pixels contains the texture data for the subimage. width and height are the dimensions of the subregion that is replacing all or part of the current texture image. xoffset and yoffset specify the texel offset in the x and y directions (with (0, 0) at the lower-left corner of the texture) and specify where to put the subimage within the existing texture array. This region may not include any texels outside the range of the originally defined texture array.