Problem with 2d rotation in OpenGL

Question

I have a function to perform sprite rotation :

void Sprite::rotateSprite(float angle){
    //Making an array of vertices - 6 for 2 triangles

    Vector2<gamePos> halfDims(_rect.w / 2, _rect.h /2);

    Vector2<gamePos> bl(-halfDims.x,-halfDims.y);
    Vector2<gamePos> tl(-halfDims.x,halfDims.y);
    Vector2<gamePos> br(halfDims.x,-halfDims.y);
    Vector2<gamePos> tr(halfDims.x,halfDims.y);


    bl = rotatePoint(bl,angle) + halfDims;
    br = rotatePoint(br,angle) + halfDims;
    tl = rotatePoint(tl,angle) + halfDims;
    tr = rotatePoint(tr,angle) + halfDims;

    /**
        1st triangle
    **/

    //Top right
    _dataPointer.vertices[0].setPosition(_rect.x+tr.x,_rect.y+tr.y);

    //Top left
    _dataPointer.vertices[1].setPosition(_rect.x+tl.x,_rect.y+tl.y);

    //Bottom left
    _dataPointer.vertices[2].setPosition(_rect.x+bl.x,_rect.y+bl.y);

    /**
        2nd triangle
    **/

    //Bottom left
    _dataPointer.vertices[3].setPosition(_rect.x+bl.x,_rect.y+bl.y);

    //Bottom right
    _dataPointer.vertices[4].setPosition(_rect.x+br.x,_rect.y+br.y);

    //Top right
    _dataPointer.vertices[5].setPosition(_rect.x+tr.x,_rect.y+tr.y);
}

Vector2<gamePos> Sprite::rotatePoint(Vector2<gamePos> pos, float& angle){

    Vector2<gamePos> newv;

    newv.x = pos.x * cos(angle) - pos.y * sin(angle);
    newv.y = pos.y * cos(angle) + pos.x * sin(angle);

    return newv;
}

And the result is

Am i doing something wrong ? It happens also when i put small angle (even if i put here angle 1 )

Thanks for help.

Answer 1

Try

angle = angle *(3.14159/180.0)
newv.x = pos.x * cos(angle) - pos.y * sin(angle);
newv.y = pos.y * cos(angle) + pos.x * sin(angle);

Trig functions works with radians so you will have to do the conversion to radians as above. as stated in the comments, It is recommended you convert the (3.14159/180.0) to a constant and use the built in PI constant instead of 3.14159.