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PO
 

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  1. PO
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    <p>thoght your question not programmatical but physical (mechanical). </p> <p>position of object can be calculated from the system of equation:</p> <pre><code>x = Vx * t + x0 y = (-g*t*t)/2 + Vy * t + y0 </code></pre> <p>, where g - Gravitational acceleration, V - initial speed, Vx and Vy - its projections on axes X and Y, respectively.</p> <p>Question is what's the highest point, i.e. we need to found MAX(y(t)). derivative: <code>y'(t) = -g*t + Vy.</code> </p> <pre><code>y'(t) should equals zero, -g*t + Vy = 0; t = Vy/g; MAX(y) = y(Vy/g) = Vy*Vy/2g. MAX(y) = Vy*Vy/2g + y0 // ballistic trajectory MIN(y) = y0 - Vy*Vy/2g // your case </code></pre> <p>End you should calculate velocity accroding to this, if you want your bird Y to be in certain range.</p> <p>Addition:</p> <blockquote> <p>btw is there a sample cocos2d code for parabola?</p> </blockquote> <p>Here is my working code.</p> <pre><code> - (void) update: (ccTime)dt { t += dt*20; ... [self getVertices]; } - (void) getVertices { //for every index: { ... //getting initial position (x0, y0) ... vertices[index] = ccpAdd(vertices[index], ccpMult(velocity[index/3], t * screenFactor)); //+velocity*t vertices[index] = ccpAdd(vertices[index], ccpMult(gravity, (t*t/2) * screenFactor)); //+acceleration*t^2 /2 //} } </code></pre> <p>1) As you can see, there's no need to calculate Velocity every time: use initial speed. 2) Vertices is CGPoint array of current Sprite positions. 3) t (current time), vertices, gravity, velocity are instance variables of common class.</p>
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    1. POcocos2d fruit ninja parabola math
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    1. COi used a CGPoint to encapsulate velocity, same as acceleration. the acceleration is positive since the birds is underwater(like fruit ninja upside down), by the way, the origin for cocos2d is bottom-left corner
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    2. COI did understood, but it's only a detail; OK, corrected formula is MIN(Y) = y0 - Vy*Vy/2g
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      1. USOleg Trakhman
    3. COi modified the code. multiply velocity by 3. just confused by the delta.
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