如何在SDL C ++中将图像移动到点

Question

i try to move particle image to the point that the player will click on the screen. i use this formula from physics to calculate speed vector.

    float x = iceBallParticle[i]->GetCurrentLocation().x - iceBallParticle[i]>GetGoToX() ;
    float y = iceBallParticle[i]->GetCurrentLocation().y - iceBallParticle[i]->GetGoToY() ;
    float c = (x/y);
    float alpha = atan(c);

    //calculate the velocity x,y
    float yVel = (speedOfMoveSkill * cos(alpha)) ; 
    float xVel = (speedOfMoveSkill * sin(alpha)) ;

        //Move Left
        if(iceBallParticle[i]->GetCurrentLocation().x > iceBallParticle[i]->GetGoToX())
            //move the object
            iceBallParticle[i]->SetCurrentLocation(iceBallParticle[i]->GetCurrentLocation().x - xVel , iceBallParticle[i]->GetCurrentLocation().y);
. . . more moves direction down here.

GoTo is where the player clicked and the current location is where the particle shot from. i think the problame is becuz he print the image by int and when i send it to print he miss the number after the point x.xxxx

  _______
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he go up and then straight, and i want him to go straight to the point

  /
 /
/

how i can to fix it?

Answer 1

I'm not exactly sure if I understand the question correctly.

One error is probably how you calculate alpha . You miss the sign of x / y by doing it that way. There is atan2 to overcome this problem. It's just:

float alpha = atan2(y, x);

But you don't need to calculate alpha at all. An easier solution would be:

float dist = sqrt(x*x + y*y);
if(dist == 0) return; // exit here to avoid div-by-zero errors.
                      // also, we are already at our point

float yVel = (speedOfMoveSkill * x / dist) ; 
float xVel = (speedOfMoveSkill * y / dist) ;

(Note that you have switched sin / cos for xVel / yVel . sin is always the y -axis, cos the x -axis.)

I think you have another error in the "move the object" code. You missed yVel there.

This might be the code you want:

//move the object
iceBallParticle[i]->SetCurrentLocation(
  iceBallParticle[i]->GetCurrentLocation().x - xVel,
  iceBallParticle[i]->GetCurrentLocation().y - yVel);

I don't really see why you have the "Move Left" check there. It should not be there.

(Btw., it is more common to calculate GoTo - GetCurLoc . Then you have the velocity with the right sign and you normally add the velocity, not subtract it.)