2D game algorithm to calculate a bullet's needed speed to hit target?

Question

I have a rather simple bird's-view 2D game where tower sprites defend against incoming moving sprites by shooting a bullet at them. My question: How do I calculate the needed bullet speed for the bullet to reach its moving target, provided that the bullet will always have the same defined speed? I'm using JavaScript and have these sprite variables (among others): sprite.x, sprite.y, sprite.width, sprite.height, sprite.speedX (i.e. velocity), sprite.speedY... so I have the objects originSprite, targetSprite and bulletSprite, all with these type of values, and I need to set the right bulletSprite speed values. Probably for it to look good, the bullet would start at the outside of the originSprite (or some defined radius, though I guess starting from the originSprite center would also work), but its bullet center would try hit into the center of the targetSprite or so. Note there's no gravity or anything in this world. (Perhaps I should have my sprites variables using angle and velocity but right now I'm using speedX and speedY...) Thanks so much!

Answer 1

I think you're trying to calculate what angle to aim the tower, you want the bullet to intercept the enemy, which they are both moving at different speeds.

You could do the easy thing: heat-seek (move towards target point each frame)

Or the easier thing: when the tower "shoots" just instantly damage the target

Or you could do the hard thing: shoot a bullet that intercepts the target. It's not a simple problem. The speeds would be constant, so you'd just calculate the position if the path were a straight line, then apply the distance from the target start to the target end onto the path.