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Create a dynamic jump |
MegaRubber
Member #22,311
January 2022
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ya the easiest way that i know is to create two jump buttons (pressed and down), and use a min (-y goes to up) function when the character is falling. i tried to use the keypressed() (not worked) and the key[] array (looks like a down button). So my question as a beginner in allegro: which function/flag i could use to detect these two types of events? (pressed and down) PS: i'm using allegro 4 and creating a platformer game |
Scooter
Member #16,799
January 2018
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Hi: |
DanielH
Member #934
January 2001
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Look into position, velocity, acceleration equations With pressing any key direction, all you're going to do is change the acceleration Velocity is based on acceleration You can split this up for x and y Position is a function of velocity and acceleration When you press the jump key. Add a negative acceleration (assuming negative is up). There is always a positive acceleration due to gravity. The negative acceleration must exceed the positive to make him jump. Gravity is a change in velocity of (9.8m/s) every second. You would need to adjust for frame rate and pixel size. How many pixels is one meter? How many frames are processed is one second? Of course any collision would drop the velocity to zero. You could base damage if velocity was too great the player hit the wall. |
MegaRubber
Member #22,311
January 2022
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Scooter said:
Hi: If you could, I would be very grateful! DanielH said: Look into position, velocity, acceleration equations With pressing any key direction, all you're going to do is change the acceleration Velocity is based on acceleration You can split this up for x and y Position is a function of velocity and acceleration When you press the jump key. Add a negative acceleration (assuming negative is up). There is always a positive acceleration due to gravity. The negative acceleration must exceed the positive to make him jump. Gravity is a change in velocity of (9.8m/s) every second. You would need to adjust for frame rate and pixel size. How many pixels is one meter? How many frames are processed is one second? Of course any collision would drop the velocity to zero. You could base damage if velocity was too great the player hit the wall. I finished the logic of variable jump and I didn't use these equations, but the logic of them, gravity, and the info about properties of the game were very helpful. thx |
Scooter
Member #16,799
January 2018
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Hi Mega: Above is 'mario.zip'. This is a very simple example of mario jumping. No physics! Use Left and Right arrow keys to move mario. Press Space Bar to make mario jump up and spin around and come back down. This uses Allegro 5 and done on Linux. You should have no problem to make it run on Allegro 4. If zip file does NOT work for you, let me know and I will send you another one. Hope this helps. Have a great day! |
Edgar Reynaldo
Major Reynaldo
May 2007
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All you need for jumping is a few simple equations. If you know the duration you want your player to be in the air, and you know the force of gravity, it's easy to predict it's max jump height. h(t) = h0 + v0*t + a*t^2 / 2 h`(t) = v0 + at h`(t/2) = v0 + at/2 = 0 a = -2v0/t h(t/2) = h0 + v0*t/2 + a*t^2/4 / 2 h(t/2) = v0*t/2 + -2v0*t^2/t/4 = v0*t/4 t is the duration, h is the height, a is the acceleration of gravity, v0 is the initial jump velocity. My Website! | EAGLE GUI Library Demos | My Deviant Art Gallery | Spiraloid Preview | A4 FontMaker | Skyline! (Missile Defense) Eagle and Allegro 5 binaries | Older Allegro 4 and 5 binaries | Allegro 5 compile guide |
RmBeer2
Member #16,660
April 2017
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In A4 you can use fixed numbers. All you have to do is add each frame the value of gravity to the object that jumps to modify the force of fall. grav = 0.2; BY JUMP: BY FRAME: You just have to adjust the values according to the game. And you may want to make it jump higher the longer the jump is held, it just adds or initializes again on 'movy'. πππ π BlackRook WebSite π C/C++ π GNU/Linux π IceCream/Cornet π πππ Rm Beer for Emperor 2021! Rm Beer for Ruinous Slave Drained 2022! Rm Beer for Traveler From The Future Warning Not To Enter In 2023! Rm Beer are building a travel machine for Go Back from 2023! |
Chris Katko
Member #1,881
January 2002
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Depending on the game, you don't even use proper physics. Many games have "fixed velocity up" for X frames, then "fixed velocity down", instead of acceleration. Depends on what you want. In that case it's like 1struct player{
2float x, y, height;
3}
4
5//attempt to start jump here (because you pressed a jump key)
6if(!is_jumping && !is_falling) //if we're not falling or jumping up, we can start a jump
7 {
8 is_jumping == true;
9 is_falling == false;
10 height = 0; //reset our jump height counter.
11 }
12
13if(is_jumping && !is_falling) //if we're jumping, add height until we reach max
14 {
15 y += 5;
16 height += 5; //track how far we've gone up since we started
17 if(height >= 100){is_jumping = false; is_falling = true;} //if we've gone far enough, stop going up
18 }
19if(!is_jumping && is_falling) //if falling, fall until we hit a floor
20 {
21 y -= 5;
22 if( we_touched_a_floor() ) {is_jumping = false; is_falling = false;}
23 }
Many older/retro games used this style. It's "one speed up/down" jumping. Instead of accelerating and decellerating. Basically what I've done above is create a finite state machine. It sounds big/complex but it's not. There are three modes or "states" that a person is in. Each state has its own set of code that runs. Whether moving you up, moving you down, or not moving you up or down. And in a real game, you'd also have in those sections code for making your character "look" like he's jumping or falling like in Mario Bros. And, mathematically, binary numbers can have only two numbers. Since we have three states, we'd need a minimum of two binary numbers (2^2 = 4 states max) to fit them in. If we wanted five states, we'd need (2^3 = 8 states max) three boolean numbers to store those possibilities. -----sig: |
amarillion
Member #940
January 2001
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Lot's of games don't actually use proper physics. There is a lot of good analysis on youtube https://www.youtube.com/watch?v=yorTG9at90g Or a search for game+design+jump will show up tons of useful stuff. -- |
Edgar Reynaldo
Major Reynaldo
May 2007
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I think we're all missing the OT. Which was how to detect keypress and keydown events in Allegro 4. https://bitbucket.org/bugsquasher/unofficial-allegro-5-binaries/downloads/Allegro443.chm That's a CHM manual for Allegro 4.4. See keypressed() and readkey(). Keep an array of keystates and when they change state that is a press or a release. When their state stays the same, that is a hold / down or open / up. while(keypressed()) {command(readkey());} My Website! | EAGLE GUI Library Demos | My Deviant Art Gallery | Spiraloid Preview | A4 FontMaker | Skyline! (Missile Defense) Eagle and Allegro 5 binaries | Older Allegro 4 and 5 binaries | Allegro 5 compile guide |
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