It is easy to rotate pixel array if the angle is a multiple of 90 degree.
For example, (quote from Computer Graphics with OpenGL)
We can rotate a two-dimensional object or pattern 90' counterwise by reversing the pixel values in each row of the array, then interchanging rows and columns.
But I could not understand how to rotate pixel array when the angle is not a multiple of 90 degree from the textbook.
Each desitination pixel area is mapped onto the rotated array and the amout of overlap with the rotated pixel areas is calculated.
Why does this means?