void glCopyTexSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLint x, GLint y, GLsizei width, GLsizei height);
void glCopyTextureSubImage2D(GLuint texture, GLint level, GLint xoffset, GLint yoffset, GLint x, GLint y, GLsizei width, GLsizei height);
The screen-aligned pixel rectangle with lower left corner at x y and with width width and height height replaces the portion of the texture array with x indices xoffset through xoffset + width - 1, inclusive, and y indices yoffset through yoffset + height - 1, inclusive, at the mipmap level specified by level.
The pixels in the rectangle 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.
The destination rectangle in the texture array may not include any texels outside 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.
When target is GL_TEXTURE_1D_ARRAY then the y coordinate and height are treated as the start slice and number of slices to modify.
If any of the pixels within the specified rectangle 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 internalformat, width, or height, parameters of the specified texture array or to texel values outside the specified subregion.
GL_INVALID_FRAMEBUFFER_OPERATION is generated if the object bound to GL_READ_FRAMEBUFFER_BINDING is not framebuffer complete.
GL_INVALID_OPERATION is generated if the texture array has not been defined by a previous glTexImage2D(), glTexStorage2D() or glCopyTexImage2D() operation.
GL_INVALID_OPERATION is generated by glCopyTextureSubImage2D if texture is not the name of an existing texture object.
GL_INVALID_OPERATION is generated by glCopyTextureSubImage2D if the effective target of texture does not correspond to one of the texture targets supported by the function.
GL_INVALID_VALUE is generated if level is less than 0.
GL_INVALID_VALUE is generated if the effective target is GL_TEXTURE_RECTANGLE and level is not zero.
GL_INVALID_VALUE may be generated if level > log 2 max, where max is the returned value of GL_MAX_TEXTURE_SIZE.
GL_INVALID_VALUE is generated if xoffset < 0, xoffset + width > w, yoffset < 0, or yoffset + height > 0,, where w is the GL_TEXTURE_WIDTH, h is the GL_TEXTURE_HEIGHT and of the texture image being modified.
GL_INVALID_OPERATION is generated if:
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