Using Java how can I plot the path of a sprite in a straight line?

Question

To illustrate I currently have something like

int startX,endX,currX;
int startY,endY,currY;

public void updatePos(){

if(currX<=endX){
   currX+=1;
}
//Same for y

I can see that I dont want to move x and y the same amount each time but dont know how to work out what I should do to determine how much each should be adjusted.

Any ideas

Maybe this will help clarify

Imagine I start at these coords (0,0) and I want to get to (18,10)

if I increment my x and y until they reach the desired target by a step of one the sprite moves diagonnally upwards then across the screen to the right before resting in the correct position.

The behaviour I want is that it travels a single direction towards the destination point (along the splope of a triangle if you will)

Im looking for suggestions on how to find my next set of points

Answer 1

Typically you will have a required velocity for your sprite and will update its position based on its velocity and the time ellapsed since it was last updated, e.g.

public class MySprite {
  int x, y; // Location
  int dx, int dy; // Velocity in pixels / millisecond

  public void updatePosition(long deltaMillis) {
    // Update x and y position based on current velocity.
    x += dx * deltaMillis;
    y += dy * deltaMillis;
  }
}

Depending on the speed of your machine your animation loop will run faster or slower. However, as your updates are based on a pre-specified velocity this will not affect the speed of the sprite moving across the screen.

public void animationLoop() {
  long prev = System.currentTimeMillis();; 
  long now;
  long deltaMillis;

  while (animationRunning) {
    // Record ellapsed time.
    now = System.currentTimeMillis();
    deltaMillis = now - prev;
    prev = now;

    if (deltaMillis > 0L) { // Some time has passed so move sprite.
      sprite.updatePosition(deltaMillis);
    }

    // TODO: Repaint sprite.
  }
}

Answer 2

If T is the time that is needed to move from X0,Y0 to X1,Y1, the position at any given time t (0 <= t <= T) is:

X = X0 + t*(X1-X0)/T
Y = Y0 + t*(Y1-Y0)/T

Answer 3

Based on your expanded question it sounds like you're interested in visiting every pixel between the start and end location. In this case you might want to take a look at Bresenham's Line Algorithm, which describes how to do this.