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I have been watching Pygame tutorials to learn the module, and it came to the portion where the instructor shows you how to make your character jump. However, I am finding it impossible to understand the code they put down, and they did not explain it very well.

Can anyone break down for me the code below so I understand exactly what is happening? And is there a simpler way of coding a jump for a character? Please keep in mind I already have the code set up to where pressing the spacebar makes this code activate.

Isjump = False
Jumpcount = 10

#code for spacebar activation here, turns Isjump to True# 

if Jumpcount >= -10:
    Neg = 1
    if Jumpcount < 0:
        Neg = -1
    y -= (Jumpcount ** 2) * 0.5 * Neg
    Jumpcount -= 1
else:
    Isjump = False
    Jumpcount = 10
Rabbid76
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Kellenwood
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    In order to make jumping believable you have to model acceleration/deceleration otherwise it won't "look right". So while you could model it more simply by doing a linear transition it would look really odd. – Jared Smith Jan 24 '21 at 19:13
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    @JaredSmith This is the code of a YouTube tutorial that will be used by almost every beginner. Of course, it's not physically correct. But it's a nice effect and not bad for learning Python. – Rabbid76 Jan 24 '21 at 19:16
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    @Rabbid76 I wasn't criticizing the code, I was trying to explain that the apparent complexity was to model (in a limited way) acceleration and deceleration. You certainly explained it better. – Jared Smith Jan 24 '21 at 20:30
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    @JaredSmith I apologize. I didn't mean to criticize you. Just wanted to realize that the code needs to be read from the perspective of a beginner who wants to learn Python. – Rabbid76 Jan 24 '21 at 20:33

1 Answers1

2

At the started Jumpcount is set 10.

Jumpcount = 10

The jump runs until Jumpcount is less or equal -10. Therefore, a jump takes exactly 21 cycles:

if Jumpcount >= -10:

Neg is "signe" of Jumpcount. It is 1 if Jumpcount is greater or equal to zero and -1 otherwise:

Neg = 1
if Jumpcount < 0:
    Neg = -1

In each frame, the player's y coordinate is changed by the quadratic function (Jumpcount ** 2) * 0.5.

y -= (Jumpcount ** 2) * 0.5 * Neg

Since this term is multiplied by Neg, it is positive if Jumpcount is greater than 0, and 0 if Jumpcount is 0, otherwise it is less than 0.
When the amount of Jumpcount is large, the change in the y coordinate is greater than when the amount is small. See the values for (Jumpcount ** 2) * 0.5 * Neg in the 21 cycles:

50.0, 40.5, 32.0, 24.5, 18.0, 12.5, 8.0, 4.5, 2.0, 0.5, 0.0, 
-0.5, -2.0, -4.5, -8.0, -12.5, -18.0, -24.5, -32.0, -40.5, -50.0

At the beginning the values are positive and the player jumps. In the end the values are negative and the player falls down.
The sum of this values is 0. Therefore the y-coordinate has the same value at the end as at the beginning.

See also How to make a character jump in Pygame?.

Rabbid76
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