The correct approach to developing games in Python

Python3 has made many improvements based on Python2, such as string encoding. The default characters in Python3 use unicode encoding, which can cover all characters on the earth. Of course, the advantages are not limited to this. In addition, the development efficiency of the Python language itself is very high, so today we teach you to use Python3 to develop a popular game - Fishing Master!

First of all, let’s have a brief understanding of the game Fishing Master. Fishing Master is a very popular game in the past few years. It is a casual competitive game with the theme of deep sea hunting. "Fishing Master" was launched in 2009 and initially won the hearts of players for its simple and easy fishing gameplay. In the following years, it won many awards including the "Top Ten Games" and the Top Ten Most Popular Mobile Online Games in 2015 issued by the Game Working Committee. Solemnly declare your status as a fishing expert. There is a game development engine in Python3 called cocos2d.

This game engine was originally an Objective-C version, which could only be used on the iOS system. Later, the domestic big-name Wang Zhe translated it into a C version. C is portable, so it quickly became popular. The cocos2d we are going to use today is the Python version. Compared with the C version, the python version of cocos2d has higher development efficiency and does not have so many wild pointers and memory leaks. It also supports cross-platform development. The game runs on Windows and Mac as well as Linux without changing a single line of code. If you have not installed this game engine, you can install it with the following command:

pip3 install cocos2d

Initialize director class:

In cocos2d, the director class is used to arrange the entire game process. And it is a singleton object during the game. The first thing to do when using cocos2d is to initialize the director:

from cocos.director import director 
director.init(width=800,height=480)   # 设置窗口的宽度是800像素，高度是400像素

Create game scenes and layers:

Scene is an integral part of game development. A scene game interface can be a scene. Scenes generally do not directly place game elements, such as fish and cannon barrels. Generally, we will put game elements in a layer, and then put this layer into the scene. The layer can also be used to receive user events, such as click events. So let's initialize the first scene and layer:

from cocos import layer
from cocos import scene
game_layer = layer.Layer()
game_scene = scene.Scene()

Add background image:

The game is played under the sea, so a picture must be used as the background of the game, otherwise the game will be boring. In cocos2d, if you want to load an image, you must use a sprite. The fish, cannon barrels, and nets that we will use in the game in the future are all implemented through sprites. And the elves should be placed in the layer. Here I inherited layer.Layer and rewrote a subclass. The code is as follows:

Add gun barrel:

The gun barrel needs to be implemented through sprites. Here I directly wrote a subclass, inherited from sprite.Sprite, and then created a gun barrel class. The code is as follows:

Receive user click events: To receive user click events, you need to do two things. First, set the class attribute of the game layer is_event_handler=True. Second, implement on_mouse_press to receive user click events. The code is as follows:

Rotating barrel:

After the user clicks on the screen, he needs to rotate the barrel and cast the net. Here, let’s rotate the barrel first. Because we only know the x and y coordinates of the screen, but not the angle, we need to use trigonometric functions to perform a conversion. The code is as follows:

net:

After rotating the barrel, the net should be cast out to the place clicked by the mouse, and the net should be enlarged from small to large when cast out. The code is as follows:

Add fish:

As of now, there is no fish in our game scene, so we add the fish class here and let it inherit from sprite.Sprite. The fish will continuously update its movements during swimming. Therefore, we cannot simply use one picture, but use a group of pictures. We call it keyframe animation. The code is as follows:

Collision detection between fish and net:

When the net is cast out, it should be judged whether there is a collision with the fish. If it collides, the fish should be set to the captured state. In cocos2d, the collision detection module has been encapsulated, which can be completed through cocos.collision_model. And if you want to add collision detection to an element, you must add a cshape attribute so that collision can occur. There is a lot of code here, so I will list it separately:

fish:

net:

Check if a collision occurs:

The above provides you with an idea. Python can still make awesome 2D games.

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