You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: buffer.go
    path of file: ./repos/gdlv/vendor/golang.org/x/exp/shiny/driver/gldriver
    
    the code of the file until where you have to start completion: // Copyright 2015 The Go Authors. A
    
func (b *bufferImpl) preUpload() {
	// Check that the program hasn't tried to modify the rgba field via the
	// pointer returned by the bufferImpl.RGBA method. This check doesn't catch
	// 100% of all cases; it simply tries to detect some invalid uses of a
	// screen.Buffer such as:
	//	*buffer.RGBA() = anotherImageRGBA
	if len(b.buf) != 0 && len(b.rgba.Pix) != 0 && &b.buf[0] != &b.rgba.Pix[0] {
		panic("gldriver: invalid Buffer.RGBA modification")
	}
}