5.5 方块特征

在上几节，我们已经了解了如何定义新的方块、如何通过方块状态和方块置换指定不同的方块特性、以及如何定义不完整方块和透明方块。但是，我们也看到为了放置特定的方块状态的方块，确实有诸多的不便。所幸，微软和 Mojang 已经考虑到这一点，并给我们提供了一些原版可用的方块状态，并附带特定的方块功能，这就是方块特征（Block Traits）。

例如，对于半砖来说，我们知道它们都是共享一个方块状态minecraft:vertical_half的（这也是为什么我们上一节把半砖的方块状态定义为test:vertical_half）。那么，使用方块特征之后，游戏引擎会试图获取玩家放置该方块的位置，并自动确定minecraft:vertical_half的值，这就不需要我们再进一步获取玩家放置该方块的位置了。因此，使用方块特征会大幅简化我们的工作量！

目前来说，原版提供的方块特征称不上多，都在我们提供的方块特征的清单里，读者可以查阅一下，了解都有什么功能后，再继续阅读教程。

定义方块特征的方法和方块状态类似，都是在方块描述里定义的:

dirt_slab.block.json
{
    "format_version": "1.21.90",
    "minecraft:block": {
        "description": {
            "identifier": "test:dirt_slab",
            "menu_category": { "category": "construction" },
            "traits": {
                "minecraft:placement_position": {
                    "enabled_states": [ "minecraft:vertical_half" ]
                }
            }
        },
        "components": {
            "minecraft:destructible_by_mining": { "seconds_to_destroy": 0.5 },
            "minecraft:destructible_by_explosion": { "explosion_resistance": 0.5 },
            "minecraft:map_color": "#976D4D",
            "tag:dirt": {},
            "minecraft:collision_box": { "origin": [ -8, 0, -8 ], "size": [ 16, 8, 16 ] },
            "minecraft:selection_box": { "origin": [ -8, 0, -8 ], "size": [ 16, 8, 16 ] },
            "minecraft:geometry": "geometry.slab",
            "minecraft:material_instances": { "*": { "texture": "flattened_dirt" } }
        },
        "permutations": [
            {
                "condition": "query.block_state('minecraft:vertical_half') == 'top'",
                "components": {
                    "minecraft:transformation": { "translation": [ 0, 0.5, 0 ] }
                }
            }
        ]
    }
}

其中，我们高亮的第 7-11 行和第 25 行的代码就是我们相比以前更改的内容。我们来做一些简单的解释：

在第 7-11 行，我们移除掉了以前定义的test:vertical_half，取而代之的是minecraft:placement_position方块特征的定义。根据文档，我们启用它的minecraft:vertical_half方块状态，这样游戏就会自动追踪玩家放置在其他方块的什么位置上，并自动确定minecraft:vertical_half状态的值，就像原版的台阶一样。
而在第 25 行，我们则是将以前判断方块状态test:vertical_half的代码无缝替换为了minecraft:vertical_half。

现在我们再进入游戏试一下，会发现除了不能合成双台阶形态外，我们定义的泥土台阶已经能够工作地很好了！至于如何把台阶变为双台阶……这就是我们的脚本要完成的任务了！

dirt_slab_1

总结

是的，这节就只有这点东西了。不骗你！不过，这节的内容虽然简单，却很重要。我们后面的练习要求读者不光要掌握minecraft:placement_position方块特征！

快速总结，方块特征（Block Traits）可以用来启用原版的方块状态和方块功能，是在方块描述里定义的。我们可以追踪方块对应的方块状态采用不同的方块置换。具体写法读者可见方块特征文档。

练习

练习 5.4

别看这节内容简单，题目可不一定简单哦！你做好心理准备了吗？

将我们上一节练习做的竖半砖“方块特征”化。
将我们上一节练习做的玻璃台阶“方块特征”化。
试还原原版的南瓜灯test:jack_o_lantern，记得和原版对比看看，暂时不用还原可生成铁傀儡雪傀儡的特性。提示：使用方块标签还原斧子和剑可加速破坏的特性。
（难度高，选做）基于minecraft:geometry组件的bone_visibility参数，试定义一种防爆玻璃板！
（难度高，选做）定义一种玻璃楼梯。~~对，字越少事越大！~~

版本适用性警告：其中第 4 题和第 5 题可能需要更高版本的组件或特征，但这些功能在中国版均存在平替，读者若需要中国版的相关功能可按需查阅。

练习题答案

BP_test/blocks/test/oak_vertical_slab.block.json 行为包定义
 {
     "format_version": "1.21.90",
     "minecraft:block": {
         "description": {
             "identifier": "test:oak_vertical_slab",
             "menu_category": { "category": "construction" },
             "traits": {
                 "minecraft:placement_direction": {
                     "enabled_states": [ "minecraft:cardinal_direction" ]
                 }
             }
         },
         "components": {
             "minecraft:collision_box": { "origin": [ -8, 0, -8 ], "size": [ 8, 16, 16 ] },
             "minecraft:selection_box": { "origin": [ -8, 0, -8 ], "size": [ 8, 16, 16 ] },
             "minecraft:geometry": "geometry.vertical_slab",
             "minecraft:material_instances": { "*": { "texture": "oak_planks" } },
             "minecraft:map_color": "#8F7748",
             "minecraft:destructible_by_mining": { "seconds_to_destroy": 2 },
             "minecraft:destructible_by_explosion": { "explosion_resistance": 3 },
             "tag:minecraft:is_axe_item_destructible": {},
             "tag:wood": {}
         },
         "permutations": [
             { "condition": "q.block_state('minecraft:cardinal_direction') == 'north'", "components": { "minecraft:transformation": { "rotation": [ 0, 90, 0 ] } } },
             { "condition": "q.block_state('minecraft:cardinal_direction') == 'west'", "components": { "minecraft:transformation": { "rotation": [ 0, 180, 0 ] } } },
             { "condition": "q.block_state('minecraft:cardinal_direction') == 'south'", "components": { "minecraft:transformation": { "rotation": [ 0, 270, 0 ] } } }
         ]
     }
 }

BP_test/blocks/test/glass_slab.block.json 行为包定义
 {
     "format_version": "1.21.90",
     "minecraft:block": {
         "description": {
             "identifier": "test:glass_slab",
             "menu_category": { "category": "construction" },
             "traits": {
                 "minecraft:placement_position": { "enabled_states": [ "minecraft:vertical_half" ] }
             }
         },
         "components": {
             "minecraft:destructible_by_mining": { "seconds_to_destroy": 0.3 },
             "minecraft:destructible_by_explosion": { "explosion_resistance": 0.3 },
             "minecraft:collision_box": { "origin": [ -8, 0, -8 ], "size": [ 16, 8, 16 ] },
             "minecraft:selection_box": { "origin": [ -8, 0, -8 ], "size": [ 16, 8, 16 ] },
             "minecraft:geometry": "geometry.slab",
             "minecraft:material_instances": {
                 "*": { "texture": "glass", "render_method": "blend", "ambient_occlusion": 0.0 },
                 "side": { "texture": "glass_slab_side", "render_method": "blend", "ambient_occlusion": 0.0 }
             }
         },
         "permutations": [
             {
                 "condition": "query.block_state('minecraft:vertical_half') == 'top'",
                 "components": { "minecraft:transformation": { "translation": [ 0, 0.5, 0 ] } }
             }
         ]
     }
 }

答案中给出的贴图都是重新定义的，没有沿用原版的贴图。这里需要对minecraft:cardinal_direction特征 y 轴旋转 180°，以和原版匹配，因为原版的南瓜头是方块面向南方时为south，而方块特征则为玩家放置时面向南方则为south，可见刚好相差 180°。

BP_test/blocks/test/glass_slab.block.json 行为包定义
{
    "format_version": "1.21.90",
    "minecraft:block": {
        "description": {
            "identifier": "test:jack_o_lantern",
            "menu_category": {
                "category": "nature"
            },
            "traits": {
                "minecraft:placement_direction": {
                    "enabled_states": [ "minecraft:cardinal_direction" ],
                    "y_rotation_offset": 180
                }
            }
        },
        "components": {
            "minecraft:geometry": "minecraft:geometry.full_block",
            "minecraft:material_instances": {
                "*": { "texture": "jack_o_lantern_side", "face_dimming": false, "ambient_occlusion": 0.0 },
                "up": { "texture": "jack_o_lantern_top", "face_dimming": false, "ambient_occlusion": 0.0 },
                "down": { "texture": "jack_o_lantern_top", "face_dimming": false, "ambient_occlusion": 0.0 },
                "south": { "texture": "jack_o_lantern_face", "face_dimming": false, "ambient_occlusion": 0.0 }
            },
            "minecraft:light_emission": 15,
            "minecraft:destructible_by_explosion": { "explosion_resistance": 1 },
            "minecraft:destructible_by_mining": { "seconds_to_destroy": 1 },
            "tag:minecraft:is_sword_item_destructible": {},
            "tag:minecraft:is_axe_item_destructible": {}
        },
        "permutations": [
            {
                "condition": "q.block_state('minecraft:cardinal_direction') == 'east'",
                "components": { "minecraft:transformation": { "rotation": [ 0, 90, 0 ] } }
            },
            {
                "condition": "q.block_state('minecraft:cardinal_direction') == 'north'",
                "components": { "minecraft:transformation": { "rotation": [ 0, 180, 0 ] } }
            },
            {
                "condition": "q.block_state('minecraft:cardinal_direction') == 'west'",
                "components": { "minecraft:transformation": { "rotation": [ 0, 270, 0 ] } }
            }
        ]
    }
}

见附录：如何制作玻璃板。
见附录：如何制作玻璃楼梯。

总结​

练习​

总结

练习