zoom relative to a center point problem

Programming Questions

mataarsak

zoom relative to a center point problem

in Programming Questions • 1 year ago

I need to zoom to my sketch relative to the fingers center point . the problem is that when I add translate to center point every thing is translated . even the position of that center point !

scale(zoom);
ellipse(centerX,centerY);
translate(width/2,height/2);

so with the above code it draw an ellipse which show the center point , and it's correct , but when I add translate to center point everything is wrong even the position of the ellipse changes ! where should I put this translate to center point ? I want to just zoom relative to center point . even when I add translate for panning the same thing is happening.

please help !

Replies(1)

Jo Wood

Re: zoom relative to a center point problem

1 year ago

The key to this is to translate the object you wish to zoom so that the bit you want to remain in the same place after zooming is at the origin (coordinates (0,0). This is therefore done with thee transformation steps:

1. Translate the origin so that it sits in the centre of your object

2. Do the zooming

3. Translate the origin back to its original position.

and

4. Draw your feature.

So in your example it might be something like

translate(centerX,centerY);

scale(zoom);

translate(-centerX,-centerY);

ellipse(centerX,centerY,20,20);

This can be abbreviated into one fewer steps by recognising that the last translate statement and the ellipse location cancel each other out:

translate(centerX,centerY);

scale(zoom);

ellipse(0,0,20,20);

Jo.

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