METHOD FOR ROTATING IMAGES
In a method for rotating geometric shape having an assigned texture image, a two dimensional outline of a rotated source geometric shape is defined by performing its perspective projection onto a two dimensional plane. Then, according to the method, the two dimensional outline is split into intermediate rectangles in places where pixel of each line non-parallel to the rotation axis of the two dimensional outline changes coordinates and for each intermediate rectangle the steps of finding a corresponding part of the texture image taking perspective correction into account. One of the last steps executes copying with scaling a corresponding part of the texture image in order to fit it into the intermediate rectangle.
1 . A method for rotating geometric shape having an assigned texture image, the method comprising the steps of
obtaining a source geometric shape with an assigned texture image;
receiving a request to rotate the source geometric shape around a rotation axis being either the X-axis or the Y-axis;
defining a two dimensional outline of a rotated source geometric shape by performing its perspective projection onto a two dimensional plane;
splitting the two dimensional outline, into intermediate rectangles, in places where pixel of either of lines, non-parallel to the rotation axis of the two dimensional outline, changes coordinates wherein in case of a rotation around the Y-axis, pixel's Y-coordinate value changes by n counted from a Y-coordinate value of a previous split point or a start point of a line non-parallel to the rotation axis of the two dimensional outline and wherein in case of a rotation around the X-axis, pixel's X-coordinate value changes by n counted from an X-coordinate value of a previous split point or a start point of a line non-parallel to the rotation axis of the two dimensional outline; and
for each intermediate rectangle finding a corresponding part of the assigned texture image, taking perspective correction into account, and copying, with scaling, the corresponding part of the assigned texture image in order to fit it into the intermediate rectangle.
2 . The method according to claim 1 wherein lines non-parallel to the rotation axis of the two dimensional outline are calculated using Bresenham algorithm.
3 . The method according to claim 1 wherein value of the n parameter is preferably 1 or −1.
4 . The method according to claim 1 wherein a blitter executes the copying and scaling tasks.
5 . The method according to claim 1 wherein an angle value of rotation is between 0 degrees and 45 degrees or 0 degrees and −45 degrees.
6 . The method according to claim 1 wherein at least one of the intermediate rectangles has four equal sides.
7 . The method according to claim 1 wherein all depth coordinates of the Z-axis of the source geometric shape have equal value.
8 . A computer program comprising program code means for performing all the steps of a method as claimed in claim 1 when said program is run on a computer.
9 . A computer readable medium having computer-executable instructions performing all the steps of the computer-implemented method according to claim 1 .