copy a two-dimensional texture subimage
glCopyTexSubImage2D( GLenum ( target ) , GLint ( level ) , GLint ( xoffset ) , GLint ( yoffset ) , GLint ( x ) , GLint ( y ) , GLsizei ( width ) , GLsizei ( height ) )-> void
glCopyTexSubImage2D replaces a rectangular portion of a two-dimensional texture image, cube-map texture image or a linear portion of a number of slices of a one-dimensional array texture with pixels from the current GL_READ_BUFFER (rather than from main memory, as is the case for glTexSubImage2D ).
The screen-aligned pixel rectangle with lower left corner at and with width width and height height replaces the portion of the texture array with x indices xoffset through , inclusive, and y indices yoffset through , 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 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.
glPixelStore modes affect texture images.
GL_INVALID_ENUM is generated if target is not GL_TEXTURE_2D , GL_TEXTURE_CUBE_MAP_POSITIVE_X , GL_TEXTURE_CUBE_MAP_NEGATIVE_X , GL_TEXTURE_CUBE_MAP_POSITIVE_Y , GL_TEXTURE_CUBE_MAP_NEGATIVE_Y , GL_TEXTURE_CUBE_MAP_POSITIVE_Z , GL_TEXTURE_CUBE_MAP_NEGATIVE_Z , or GL_TEXTURE_1D_ARRAY .
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 , where is the returned value of GL_MAX_TEXTURE_SIZE .
GL_INVALID_VALUE is generated if , , , or , where is the GL_TEXTURE_WIDTH , is the GL_TEXTURE_HEIGHT and of the texture image being modified.
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