A three-dimensional printer comprising: a delivery device to selectively deliver liquid droplets onto a layer of build materials as the delivery device is scanned across the layer; and a controller to: access a morphology of a part to be formed from the build materials in the layer ; determine, based upon the accessed morphology, a first delivery pattern for the delivery device to selectively deliver liquid droplets onto build materials in the layer during a first pass over the layer and a second delivery pattern for the delivery device to selectively deliver liquid droplets onto build materials in the layer during a second pass over the layer to control a property of the part formed of some of the build materials in the layer , wherein the first pass and second pass both comprise moving the delivery device across the layer in the same direction; and control the delivery device to selectively deliver liquid droplets onto build materials in the layer according to the determined first delivery pattern during the first pass and according to the determined second delivery pattern during the second pass ; characterised in that , placements on the layer at which liquid droplets are to be delivered according to the second delivery pattern coincide with at least some placements on the layer at which liquid droplets are to be delivered according to the first delivery pattern. a delivery device to selectively deliver liquid droplets onto a layer of build materials as the delivery device is scanned across the layer; and a controller to: access a morphology of a part to be formed from the build materials in the layer ; determine, based upon the accessed morphology, a first delivery pattern for the delivery device to selectively deliver liquid droplets onto build materials in the layer during a first pass over the layer and a second delivery pattern for the delivery device to selectively deliver liquid droplets onto build materials in the layer during a second pass over the layer to control a property of the part formed of some of the build materials in the layer , wherein the first pass and second pass both comprise moving the delivery device across the layer in the same direction; and control the delivery device to selectively deliver liquid droplets onto build materials in the layer according to the determined first delivery pattern during the first pass and according to the determined second delivery pattern during the second pass ; characterised in that , placements on the layer at which liquid droplets are to be delivered according to the second delivery pattern coincide with at least some placements on the layer at which liquid droplets are to be delivered according to the first delivery pattern. access a morphology of a part to be formed from the build materials in the layer ; determine, based upon the accessed morphology, a first delivery pattern for the delivery device to selectively deliver liquid droplets onto build materials in the layer during a first pass over the layer and a second delivery pattern for the delivery device to selectively deliver liquid droplets onto build materials in the layer during a second pass over the layer to control a property of the part formed of some of the build materials in the layer , wherein the first pass and second pass both comprise moving the delivery device across the layer in the same direction; and control the delivery device to selectively deliver liquid droplets onto build materials in the layer according to the determined first delivery pattern during the first pass and according to the determined second delivery pattern during the second pass ; characterised in that , placements on the layer at which liquid droplets are to be delivered according to the second delivery pattern coincide with at least some placements on the layer at which liquid droplets are to be delivered according to the first delivery pattern. <EOS>