Graphics: The image rotates around a point P (A, A, b)------Vernacular edition

Premise: In the study of graphics, we do not specify the size of the graph, so any graphics are supported, this also shows that the graphic conversion and the size of the graph is not related.

If the image rotates around a point P (A, A, b), the coordinate system is first panned to that point, then rotated, and the rotated image is translated back to the original coordinate origin.

-----The interpretation of this sentence, I have always thought that is to translate the coordinate system to the center of the image .... It's not, because it doesn't specify the image size, so it just pans to the point of rotation. Look carefully. There is also a point not to think of objects as a specific small square. This is always misunderstood, because the rotating object is to support any object rotation, so it should be understood that the object is wireless large, any object is supported. This also shows that the computer only supports the basic Graphics transformation-----Image transformation based on the origin point. -----So do not have any relationship between the point of rotation of the object and the center point.  Don't confuse .....  So the basic graphics transformation of the object supports the rotation point not the transformation of the center point of the object. --------if the center point and the rotation point of the object are confused. The object rotates around a certain point you don't understand.

The rotation definition of a computer that only supports the basic transformation of an object is: only the transformation of the rotation point to the origin is supported.  The rotation point is not the center point of the object. There is no relationship between the basic transformation and the size position of the graphic ....

We need 3 steps:

1. Pan -shifts the coordinate system to the point P (A, b);

2. rotate --rotate the image at the center of the original point;

3. Pan -translates the rotated image back to the original coordinate origin;

Comparing the geometric changes of the previously mentioned images (basic geometric variations of the images), this requires a translation - - rotation - - translation , which requires a geometric change of multiple images called composite changes of the image.

------These three steps another way to explain: http://itc.bnuep.com/computer/Upload/CG-7-transformation.swf-----speak good ....

Graphics: The image rotates around a point P (A, A, b)------Vernacular edition