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Help with projectiles... [RESOLVED]

by Randy Lutcavich · in Torque X 2D · 09/26/2009 (5:44 am) · 5 replies

I'm not sure what the best way of firing a projectile at an odd angle (not Left/Right or Top/Down) is.

I'm using the AI from the blaster tutorial to kind of give me some guidance in figuring out how to shoot projectiles at odd angles.

I don't know what this code means though:
int DirectionX = (TargetX > SceneObject.Position.X) ? 1 : -1;

The way the code works now is the enemy is sent from the top of the screen to the bottom by setting its Y velocity to a negative number but along the way X velocity is dynamically updated depending on the direction to the player object. My confusion comes in with the line above when declaring the X direction... what does the last part mean/do (? 1 : -1)?
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Torque Owner Lucas Shinkovich
#1
09/26/2009 (10:21 am)
Hi Randy,

The code you are referring to is officially called the conditional operator, you can read more about it on MSDN here: http://msdn.microsoft.com/en-us/library/ty67wk28(VS.80).aspx. Some people also call it the ternary operator comming from C++.

I'm not sure what you mean about odd angles to shoot projectiles but I use the following code to shoot projectiles in my game:

//Apply velocity to the projectile
            projectile.Physics.VelocityX = (float)Math.Sin(MathHelper.ToRadians(projectile.Rotation)) * _shotSpeed;
            projectile.Physics.VelocityY = -(float)Math.Cos(MathHelper.ToRadians(projectile.Rotation)) * _shotSpeed;

This is of course assuming you have done a few things ahead of time. You have a projectile (this is the variable projectile above) already created and rotated in the direction you would like to fire it. The projectile has the physics component so a velocity can be applied to it. You have defined a speed for the projectile (this is the variable (_shotSpeed above).

Torque Owner Randy Lutcavich
#2
09/26/2009 (8:01 pm)
You sir, rock!

It has been too long since Trig.

Thank you, my projectiles now shoot in the correct direction.

I will also look into the ?: conditional operator.

Torque Owner Randy Lutcavich
#3
09/26/2009 (8:06 pm)
Ok I understand the point of ?: now...

In the code I showed above:
int DirectionX = (TargetX > SceneObject.Position.X) ? 1 : -1;

An int variable (DirectionX) is being assigned either the value '1' or the value '-1'. If the conditional statement (TargetX > SceneObject.Position.X) is true than the value after the question mark (1) will be assigned. If the statement is false, the value after the semicolon (-1) is assigned.

Associate John Kanalakis
EnvyGames
#4
09/26/2009 (9:07 pm)
Just for the record, I don't like the conditional operator and usually try to avoid it. Though it works well for shorthand, it definitely makes code less readable and is a pain to follow when step-debugging. I always encourage others to use simple if/else statements instead.

John K.
www.envygames.com

Torque Owner Randy Lutcavich
#5
09/26/2009 (9:09 pm)
You are definitely right about it causing extra confusion, John. I would have had no trouble understanding a simple if/else statement.

But it is nice to know what it means in case I run across it again. I most likely won't use it though.