Rotate sprite image according to user touch location? - iphone

Question

I m start learning game development. As a beginner i create one demo game in which one cannon hit bullets to the enemies (coming toward cannon from different direction).
Now i stuck on cannon sprite image rotation anywhere user touch on the screen or enemies. How i do that, My initial code as following,
void HelloWorld:: ccTouchesBegan(CCSet *touches, CCEvent * event)
{
CCSize winSize = CCDirector::sharedDirector()->getWinSize();
CCTouch* touch = (CCTouch*)( touches->anyObject() );
CCPoint location = touch->locationInView(touch->view());
location = CCDirector::sharedDirector()->convertToGL(location);
//Rotate cannon direction toward touch point
CCPoint diffPoint = ccpSub(_cannonImage->getPosition(), location);
float angleRadians = atanf((float)diffPoint.y/(float)diffPoint.x);
float angleOffset = CC_DEGREES_TO_RADIANS(180);
if(diffPoint.x < 0){
angleRadians += angleOffset;
}else{
angleRadians -= angleOffset;
}
CCLog("angle to be rotate = %f", angleRadians);
_cannonImage->runAction(CCRotateBy::actionWithDuration(0.1, angleRadians));
}
The code is written in cocos2d-x . I also accepting answer by someone who written in plain cocos2d.
Thanks
iHungry

Answer 1

The perfect answer as follows,
float HelloWorld::changingAngleAccordingToCoordinateSystem(CCPoint imageCenter, CCPoint touchLocation, float calculatedAngle){
//Consideration :- all Angles is in Degree
if((calculatedAngle >= 0 && calculatedAngle <= 90) || (calculatedAngle >= 90 && calculatedAngle <= 180)){
//Ist quardant
calculatedAngle = calculatedAngle;
}
else if(calculatedAngle < 0 && calculatedAngle >= -90){
//IInd quardant
calculatedAngle = 270 + (90 + calculatedAngle);
}
else if(calculatedAngle < -90 && calculatedAngle >= -180){
calculatedAngle = 180 + (180 + calculatedAngle);
}
return calculatedAngle;
}
//Rotate cannon direction toward touch point
float diff_X = touchLocation.x - myImage->getPosition().x;
float diff_Y = touchLocation.y - myImage->getPosition().y;
CCPoint diffPoint = CCPoint(diff_X, diff_Y);
float angleRadians = atan2f(diffPoint.y,diffPoint.x);
angleRadians = CC_RADIANS_TO_DEGREES(angleRadians);
angleRadians = HelloWorld::changingAngleAccordingToCoordinateSystem(myImage->getPosition(), touchLocation, angleRadians);
myImage->setRotation(-angleRadians);

Answer 2

i used this code to rotate my sprite. i Was moving the sprite according to my accelerometer reading.
float angleRadians =-accelX;
float angleDegrees = CC_RADIANS_TO_DEGREES(angleRadians);
objGlider->sprite_Glider.rotation = cocosAngle;
Check it. The reason of slow may be that you may be using CClog or NSLog in the code.
Here goes the complete code.
if(!boolPlayerDied)
{
static float prevX=0, prevY=0;
#define kFilterFactor 1.0f// don't use filter. the code is here just as an example
float accelX = (float) acceleration.x * kFilterFactor + (1- kFilterFactor)*prevX;
float accelY = (float) acceleration.y * kFilterFactor + (1- kFilterFactor)*prevY;
prevX = accelX;
prevY = accelY;
accelX = accelX-0.5;// Angle check fot tgfor the player to play
float angleRadians =-accelX;
float angleDegrees = CC_RADIANS_TO_DEGREES(angleRadians);
if(accelX>0)
{
cocosAngle = 1.1 * angleDegrees;
}
else
{
if(accelX<-0.5)
accelX=-0.5;
cocosAngle = 1.1 * angleDegrees;
}
objGlider->sprite_Glider.rotation = cocosAngle;
}
objGlider is the object of the class which creates glider sprite and sprite_Glider is the sprite used in glider class.
you can use rotation property with your sprite to be rotated. In cocos2Dx it might be setRotation.

Answer 3

First of all, replace
float angleRadians = atanf((float)diffPoint.y/(float)diffPoint.x);
float angleOffset = CC_DEGREES_TO_RADIANS(180);
if(diffPoint.x < 0){
angleRadians += angleOffset;
}else{
angleRadians -= angleOffset;
}
by
float angleRadians = atan2f(diffPoint.y, diffPoint.x);
Then it would be better to set rotation immediately (without actions) to process multiple frequent touches.
_cannonImage->setRotation(angleRadians);
Maybe you will need to adjust rotation like setRotation(-angleRadians) or setRotation(angleRadians+90) - it depends on your coordinate system.