I believe it would start at (0,0) and then move to (0,2). You can check this out by creating your own conv2d layer, inputting a simple array like [[1,2,3], [4,5,6], [7,8,9] to torch.tensor as your input image (so 1 channel in and 1 channel out), and then setting the weight of the conv layer to be all 1s and its bias to be 0, and then observing the result, which I believe should be [[1,3], [7, 9]].