Question: I want to know how much initial x speed my projectile object needs in order to hit a target object that is, d, pixels away, and the projectile object has gravity = g. I have done this using time as a factor, but I don't want to have to use time to calculate the position of the projectile. I want to set the gravity of the projectile, then calculate the initial x speed needed to hit the target object as both, gravity and x speed are applied every frame. Is this possible? Thanks!

At what angle is the projectile being fired?

EDITED: Oops, accidental double post.

I guess 0 degrees. Imagine the object on the top of a cliff and is only having an initial velocity in the x coordinate. So, angles don't need to be used in this scenario (luckily).

You mean like throwing a projectile at a certain speed so that it goes right on top of the enemy?

I would use a kinematic equation to find the time needed. Specifically, probably this one: [code]v[f] = v[i] + a * t[/code] Solved for [i]t[/i], that gives us: [code]t = (v[f] - v[i]) / a[/code] So if the initial vertical velocity is called "yv" and the vertical downward acceleration is called "g", you might use this: [code]time = 2 * yv / g[/code] Then just multiply that by the horizontal velocity to get the distance. EDIT: Or rather, divide that from the distance to get the horizontal velocity. :) But if your game's acceleration is nothing more than simplistic additions to velocity variables each frame (which is what Game Maker does if I'm not mistaken), that won't actually work. In that case, the only way I can think of other than hardcoding it is to use looping to simulate the trajectory. If you do have to do this, keeping a table of previously calculated distances can help with performance. EDIT: Such a loop might look like this: [syntax=python] time_ = 0 y = 0 yv_prediction = yv while y <= 0: y += yv_prediction yv_prediction += g time_ += 1 [/syntax]

I made a code for the Fire Nipper from SMB3, if that's what you mean.

@onpon4 - Yes, that is what I did previously, and it worked. However, I was wondering if I could find the initial velocity without needing the time, I see that it's probably not possible (unless of course you simulate it as your exampled had shown). I really appreciate you taking the time to write out an explanation, by the way. @P-Star7 - Yes, minus the actually throwing part. More like, pushing an object off a cliff.

[quote]I was wondering if I could find the initial velocity without needing the time[/quote] You mean, without even accounting for the existence of time? No, that's not possible because of really basic mathematical principles. Displacement, after all, is nothing more than a factor of time and velocity, so how could you figure out the velocity for a particular displacement without also considering the time? That would be like figuring out the volume of a glass without considering its height. Of course some situations might enable the use of geometry too (depending on exactly what sort of arc it is), but I wouldn't see the point in that if simple equations will do. It's not like you lose anything by involving time into the equation. You could even break it down into a single equation if you really want to: [code]xv = xdist * g / (2 * yv)[/code]

Why is y velocity in the denominator? Y velocity in the scenario I was explaining would be 0. Unless I am missing something.

Could you draw the scenario and include what you want to be fixed or given (ex yVel is limited to zero)?

[quote]Why is y velocity in the denominator?[/quote] Because you divide distance by time to get speed. The y velocity is just a part of the calculation for time. [quote]Y velocity in the scenario I was explaining would be 0.[/quote] Oh? So it's traveling in a straight line to the right or left? If that's the case, then your question doesn't make any sense. If the projectile is traveling in a straight line, then any velocity in the correct direction will work. It's just a matter of how long it will take. I agree with TheShyGuy, you should probably draw exactly what kind of movement you're talking about.

Well, I did mention it in a previous post, you must have missed it. Ok, I'll post a picture.

Anyone with knowledge in physics will tell you that calculating velocity without time is kind of dumb, since [code] v = s/t [/code] Then again, your question and follwing replies have been pretty confusing so I might've misunderstood your problem in the first place.

The initial question is inadequate. What does "d" pixels away mean? You're talking about a 2D situation. D pixels away in the x-axis? Y-axis? If it's the x-axis, then you also need a height. Since you said an angle of 0°, that's basically like kicking something off a cliff to hit something below.