hello! in my 2d game i would like to create my playerbob can jump via pressing any key... my only problem is that i dont know a algorithm for let the player jump 40 pixels high or higher in a smooth circle using velosity and so on... i hop my bad english can explain my probl. thanks for any help elmo

well, at it's most basic, here's how you would move a player via velocity every frame:

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//somewhere at a global level
Vec3D Velocity; //x/y/z vector
Xform3D xform; //player's 4x4 transform matrix

//inside your game loop
if (!(Velocity <= 0) && !OnGroundPlane)
Velocity -= Gravity;

if (MoveForward)
Velocity += GetForward(xform) * MoveScale;
if (MoveBackward)
Velocity += -GetForward(xform) * MoveScale;
if (MoveLeft)
Velocity += GetLeft(xform) * MoveScale;
if (MoveRight)
Velocity += -GetLeft(xform) * MoveScale;

if (Jump && !OnGroundPlane) {
Velocity += GetUp(xform) * JumpForce;
OnGroundPlane = false; //prevent multiple jumps
}

if (OnGroundPlane)
Velocity -= Friction;

ClampVelocity(Velocity, 10.0f);

if (Velocity < 0.01f)
Velocity = 0;

===============================

that's fairly simple and should get you going.

Edited by - revolver on 3/20/00 9:50:36 AM

sorry but i dont understand nothing of this...perhaps today is stupid day, or my teethdoc has deleted my brain yesterday

normaly my ypos of my player are defined as:
ypos=ypos-speed; for jumping and ypos=ypos+speed for falling down...

but my probl. is the var speed - i must have linear values, so speed is first 6 pixel than 4 pixel than 3, than 2, than 1 and so on... but in my game i have different jumphights from 40 to 100 pixels high (its a plattform game) so how to create a linear value list for speed?

thanks for all
elmo

hm.. your problem is not really clearly defined here. I could take the complex viewpoint, which means that you want to have a character be able to jump to exactly 40 or 100 pixels in a specified time frame, which would require some physics to get right. If that is the case I will reply again.

But, the simple case would be just that you want the character to jump and fall in a parabolic fashion, which can be approximated very easily. Just have 3 variables,
y position, y speed and y acceleration (make these all floats). Here are the steps you would need to go through to make a person jump:

Step 1:
ypos = 0; // at ground
yspd = 0.1; // 0.1 pixels per frame
yaccel = -0.001; // acceleration in a downwards direction

Step 2: (do this every frame)
ypos += yspd;
yspd += yaccel;

and there you have it, gravity modeled realistically enough for a platform game.

ahhh... thats a good example...thanks
i will try it this way

thanks for all
elmo