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# How do I rotate a rectangle with the four vertices

## 3 posts in this topic

Hi,

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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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)
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Thank you so much...

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

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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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