Algorithm to shoot at a target in a 3d game
- by Sebastian Bugiu
For those of you remembering Descent Freespace it had a nice feature to help you aim at the enemy when shooting non-homing missiles or lasers: it showed a crosshair in front of the ship you chased telling you where to shoot in order to hit the moving target.
I tried using the answer from http://stackoverflow.com/questions/4107403/ai-algorithm-to-shoot-at-a-target-in-a-2d-game?lq=1 but it's for 2D so I tried adapting it.
I first decomposed the calculation to solve the intersection point for XoZ plane and saved the x and z coordinates and then solving the intersection point for XoY plane and adding the y coordinate to a final xyz that I then transformed to clipspace and put a texture at those coordinates. But of course it doesn't work as it should or else I wouldn't have posted the question.
From what I notice the after finding x in XoZ plane and the in XoY the x is not the same so something must be wrong.
float a = ENG_Math.sqr(targetVelocity.x) + ENG_Math.sqr(targetVelocity.y) -
ENG_Math.sqr(projectileSpeed);
float b = 2.0f * (targetVelocity.x * targetPos.x +
targetVelocity.y * targetPos.y);
float c = ENG_Math.sqr(targetPos.x) + ENG_Math.sqr(targetPos.y);
ENG_Math.solveQuadraticEquation(a, b, c, collisionTime);
First time targetVelocity.y is actually targetVelocity.z (the same for targetPos) and the second time it's actually targetVelocity.y.
The final position after XoZ is
crossPosition.set(minTime * finalEntityVelocity.x + finalTargetPos4D.x, 0.0f,
minTime * finalEntityVelocity.z + finalTargetPos4D.z);
and after XoY
crossPosition.y = minTime * finalEntityVelocity.y + finalTargetPos4D.y;
Is my approach of separating into 2 planes and calculating any good? Or for 3D there is a whole different approach?
sqr() is square not sqrt - avoiding a confusion.
