GLint level, GLint xoffset, GLint yoffset, GLint x, GLint y, GLsizei width, GLsizei height )
eqn not supported
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 glCopyPixels 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 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.
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, height, or border parameters of the specified texture array or to texel values outside the specified subregion.
Texturing has no effect in color index mode.
glPixelStore and glPixelTransfer modes affect texture images in exactly the way they affect glDrawPixels.
When the GL_ARB_imaging extension is supported, the RGBA components read from the framebuffer may be processed by the imaging pipeline. See glTexImage1D for specific details.
GL_INVALID_OPERATION is generated if the texture array has not been defined by a previous glTexImage2D or glCopyTexImage2D operation.
GL_INVALID_VALUE is generated if level is less than 0.
GL_INVALID_VALUE may be generated if level is greater than $log sub 2 max$, where $max$ is the returned value of GL_MAX_TEXTURE_SIZE.
GL_INVALID_VALUE is generated if x$ ~<~ ~-b$ or if y$ ~<~ ~-b$, where $b$ is the border width of the texture array.
GL_INVALID_VALUE is generated if $"xoffset" ~<~ -b$, (xoffset$~+~$width)$~>~(w ~-~b)$, yoffset$~<~ ~-b$, or (yoffset$~+~$height)$~>~(h ~-~b)$, where $w$ is the GL_TEXTURE_WIDTH, $h$ is the GL_TEXTURE_HEIGHT, and $b$ is the GL_TEXTURE_BORDER of the texture image being modified. Note that $w$ and $h$ include twice the border width.
GL_INVALID_OPERATION is generated if glCopyTexSubImage2D is executed between the execution of glBegin and the corresponding execution of glEnd.
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