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POCocos2D-x tutorial. Target's position
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copied!<p>I'm having trouble to understand the math behind a piece of code of a tutorial of cocos2d. This piece of code is about getting the target's position of a bullet</p> <pre><code>void HelloWorld::ccTouchesEnded(CCSet* touches, CCEvent* event) { // Choose one of the touches to work with CCTouch* touch = (CCTouch*)( touches->anyObject() ); CCPoint location = touch->getLocationInView(); location = CCDirector::sharedDirector()->convertToGL(location); // Set up initial location of projectile CCSize winSize = CCDirector::sharedDirector()->getWinSize(); CCSprite *projectile = CCSprite::create("Projectile.png", CCRectMake(0, 0, 20, 20)); projectile->setPosition( ccp(20, winSize.height/2) ); // Determinie offset of location to projectile int offX = location.x - projectile->getPosition().x; int offY = location.y - projectile->getPosition().y; // Bail out if we are shooting down or backwards if (offX <= 0) return; // Ok to add now - we've double checked position this->addChild(projectile); // Determine where we wish to shoot the projectile to int realX = winSize.width + (projectile->getContentSize().width/2); float ratio = (float)offY / (float)offX; int realY = (realX * ratio) + projectile->getPosition().y; CCPoint realDest = ccp(realX, realY); // Determine the length of how far we're shooting // My comment: if in the next two lines we use (offX, offY) instead of (realX, realY) // bullet direction looks ok int offRealX = realX - projectile->getPosition().x; int offRealY = realY - projectile->getPosition().y; float length = sqrtf((offRealX * offRealX) + (offRealY * offRealY)); float velocity = 480/1; // 480pixels/1sec float realMoveDuration = length/velocity; // Move projectile to actual endpoint projectile->runAction( CCSequence::create( CCMoveTo::create(realMoveDuration, realDest), CCCallFuncN::create(this, callfuncN_selector(HelloWorld::spriteMoveFinished)), NULL) ); // Add to projectiles array projectile->setTag(2); _projectiles->addObject(projectile); } </code></pre> <p>What I don't understand is the calculation of 'realY'. It looks like that it multiplies'ratio' as a tangent.</p> <p>Thanks very much in advance</p>

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