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How do I rotate a rectangle with the four vertices


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#1 Sam Sandeep   Members   -  Reputation: 123

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Posted 08 January 2013 - 03:57 AM

Hi,

 

Could anyone please help me out here?

 

I have the top left corner co ordinates of a rectangle.  And also the width and height.  Now, say, I want to rotate the rectangle 30 deg with the top left vertex as it s axis.  How do I calculate the four vertices.  

 

I'm trying to do this in opengl without using the glRotatef function, but for some reason the texture gets distorted with the rectangle rotates.

 

I'm currently using this logic.

 

 

 

currentTopLeftX = Vertices[ 0 ].x;
currentTopLeftY = Vertices[ 0 ].y;


currentTopRightX = Vertices[ 0 ].x + w*cos(angle*PI/180);
currentTopRightY = Vertices[ 0 ].y + w*sin(angle*PI/180);


currentBottomRightX = Vertices[ 0 ].x + w*cos(angle*PI/180) - h*sin(angle*PI/180);
currentBottomRightY = Vertices[ 0 ].y + w*sin(angle*PI/180) - h*cos(angle*PI/180);


currentBottomLeftX = Vertices[ 0 ].x + h*sin(angle*PI/180);
currentBottomLeftY = Vertices[ 0 ].y + h*cos(angle*PI/180);

 

 



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#2 PastelOgre   Members   -  Reputation: 140

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Posted 08 January 2013 - 05:15 AM

Equation for rotating a point around a center:
(x2,y2) = resulting rotated point
(x1,y1) = original point before rotation
(xc,yc) = center of rotation
x2 = xc+(x1-xc)*cos(angle)-(y1-yc)*sin(angle)
y2 = yc+(x1-xc)*sin(angle)+(y1-yc)*cos(angle)


#3 Sam Sandeep   Members   -  Reputation: 123

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Posted 08 January 2013 - 06:02 AM

Thank you so much... 

 

I'll try it out and let you know.. :D



#4 Sam Sandeep   Members   -  Reputation: 123

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Posted 08 January 2013 - 06:09 AM

Equation for rotating a point around a center:
(x2,y2) = resulting rotated point
(x1,y1) = original point before rotation
(xc,yc) = center of rotation
x2 = xc+(x1-xc)*cos(angle)-(y1-yc)*sin(angle)
y2 = yc+(x1-xc)*sin(angle)+(y1-yc)*cos(angle)

 

 

Wow awesome.. it works...  

 

Phew..  and it is so simple.. :|






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