tnrotate.c - plan9port - [fork] Plan 9 from user space
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tnrotate.c (5821B)
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1 /*
2 * Rotate an image 180° in O(log Dx + log Dy)
3 * draw calls, using an extra buffer the same size
4 * as the image.
5 *
6 * The basic concept is that you can invert an array by
7 * inverting the top half, inverting the bottom half, and
8 * then swapping them.
9 *
10 * This is usually overkill, but it speeds up slow remote
11 * connections quite a bit.
12 */
13
14 #include <u.h>
15 #include <libc.h>
16 #include <bio.h>
17 #include <draw.h>
18 #include <thread.h>
19 #include <cursor.h>
20 #include "page.h"
21
22 int ndraw = 0;
23
24 enum {
25 Xaxis,
26 Yaxis,
27 };
28
29 static void reverse(Image*, Image*, int);
30 static void shuffle(Image*, Image*, int, int, Image*, int, int);
31 static void writefile(char *name, Image *im, int gran);
32 static void halvemaskdim(Image*);
33 static void swapranges(Image*, Image*, int, int, int, int);
34
35 /*
36 * Rotate the image 180° by reflecting first
37 * along the X axis, and then along the Y axis.
38 */
39 void
40 rot180(Image *img)
41 {
42 Image *tmp;
43
44 tmp = xallocimage(display, img->r, img->chan, 0, DNofill);
45 if(tmp == nil)
46 return;
47
48 reverse(img, tmp, Xaxis);
49 reverse(img, tmp, Yaxis);
50
51 freeimage(tmp);
52 }
53
54 Image *mtmp;
55
56 static void
57 reverse(Image *img, Image *tmp, int axis)
58 {
59 Image *mask;
60 Rectangle r;
61 int i, d;
62
63 /*
64 * We start by swapping large chunks at a time.
65 * The chunk size should be the largest power of
66 * two that fits in the dimension.
67 */
68 d = axis==Xaxis ? Dx(img) : Dy(img);
69 for(i = 1; i*2 <= d; i *= 2)
70 ;
71
72 r = axis==Xaxis ? Rect(0,0, i,100) : Rect(0,0, 100,i);
73 mask = xallocimage(display, r, GREY1, 1, DTransparent);
74 mtmp = xallocimage(display, r, GREY1, 1, DTransparent);
75
76 /*
77 * Now color the bottom (or left) half of the mask opaque.
78 */
79 if(axis==Xaxis)
80 r.max.x /= 2;
81 else
82 r.max.y /= 2;
83
84 draw(mask, r, display->opaque, nil, ZP);
85 writefile("mask", mask, i);
86
87 /*
88 * Shuffle will recur, shuffling the pieces as necessary
89 * and making the mask a finer and finer grating.
90 */
91 shuffle(img, tmp, axis, d, mask, i, 0);
92
93 freeimage(mask);
94 }
95
96 /*
97 * Shuffle the image by swapping pieces of size maskdim.
98 */
99 static void
100 shuffle(Image *img, Image *tmp, int axis, int imgdim, Image *mask, int maskdim)
101 {
102 int slop;
103
104 if(maskdim == 0)
105 return;
106
107 /*
108 * Figure out how much will be left over that needs to be
109 * shifted specially to the bottom.
110 */
111 slop = imgdim % maskdim;
112
113 /*
114 * Swap adjacent grating lines as per mask.
115 */
116 swapadjacent(img, tmp, axis, imgdim - slop, mask, maskdim);
117
118 /*
119 * Calculate the mask with gratings half as wide and recur.
120 */
121 halvemaskdim(mask, maskdim, axis);
122 writefile("mask", mask, maskdim/2);
123
124 shuffle(img, tmp, axis, imgdim, mask, maskdim/2);
125
126 /*
127 * Move the slop down to the bottom of the image.
128 */
129 swapranges(img, tmp, 0, imgdim-slop, imgdim, axis);
130 moveup(im, tmp, lastnn, nn, n, axis);
131 }
132
133 /*
134 * Halve the grating period in the mask.
135 * The grating currently looks like
136 * ####____####____####____####____
137 * where #### is opacity.
138 *
139 * We want
140 * ##__##__##__##__##__##__##__##__
141 * which is achieved by shifting the mask
142 * and drawing on itself through itself.
143 * Draw doesn't actually allow this, so
144 * we have to copy it first.
145 *
146 * ####____####____####____####____ (dst)
147 * + ____####____####____####____#### (src)
148 * in __####____####____####____####__ (mask)
149 * ===========================================
150 * ##__##__##__##__##__##__##__##__
151 */
152 static void
153 halvemaskdim(Image *m, int maskdim, int axis)
154 {
155 Point δ;
156
157 δ = axis==Xaxis ? Pt(maskdim,0) : Pt(0,maskdim);
158 draw(mtmp, mtmp->r, mask, nil, mask->r.min);
159 gendraw(mask, mask->r, mtmp, δ, mtmp, divpt(δ,2));
160 writefile("mask", mask, maskdim/2);
161 }
162
163 /*
164 * Swap the regions [a,b] and [b,c]
165 */
166 static void
167 swapranges(Image *img, Image *tmp, int a, int b, int c, int axis)
168 {
169 Rectangle r;
170 Point δ;
171
172 if(a == b || b == c)
173 return;
174
175 writefile("swap", img, 0);
176 draw(tmp, tmp->r, im, nil, im->r.min);
177
178 /* [a,a+(c-b)] gets [b,c] */
179 r = img->r;
180 if(axis==Xaxis){
181 δ = Pt(1,0);
182 r.min.x = img->r.min.x + a;
183 r.max.x = img->r.min.x + a + (c-b);
184 }else{
185 δ = Pt(0,1);
186 r.min.y = img->r.min.y + a;
187 r.max.y = img->r.min.y + a + (c-b);
188 }
189 draw(img, r, tmp, nil, addpt(tmp->r.min, mulpt(δ, b)));
190
191 /* [a+(c-b), c] gets [a,b] */
192 r = img->r;
193 if(axis==Xaxis){
194 r.min.x = img->r.min.x + a + (c-b);
195 r.max.x = img->r.min.x + c;
196 }else{
197 r.min.y = img->r.min.y + a + (c-b);
198 r.max.y = img->r.min.y + c;
199 }
200 draw(img, r, tmp, nil, addpt(tmp->r.min, mulpt(δ, a)));
201 writefile("swap", img, 1);
202 }
203
204 /*
205 * Swap adjacent regions as specified by the grating.
206 * We do this by copying the image through the mask twice,
207 * once aligned with the grading and once 180° out of phase.
208 */
209 static void
210 swapadjacent(Image *img, Image *tmp, int axis, int imgdim, Image *mask, int maskdim)
211 {
212 Point δ;
213 Rectangle r0, r1;
214
215 δ = axis==Xaxis ? Pt(1,0) : Pt(0,1);
216
217 r0 = img->r;
218 r1 = img->r;
219 switch(axis){
220 case Xaxis:
221 r0.max.x = imgdim;
222 r1.min.x = imgdim;
223 break;
224 case Yaxis:
225 r0.max.y = imgdim;
226 r1.min.y = imgdim;
227 }
228
229 /*
230 * r0 is the lower rectangle, while r1 is the upper one.
231 */
232 draw(tmp, tmp->r, img, nil,
233 }
234
235 void
236 interlace(Image *im, Image *tmp, int axis, int n, Image *mask, int gran)
237 {
238 Point p0, p1;
239 Rectangle r0, r1;
240
241 r0 = im->r;
242 r1 = im->r;
243 switch(axis) {
244 case Xaxis:
245 r0.max.x = n;
246 r1.min.x = n;
247 p0 = (Point){gran, 0};
248 p1 = (Point){-gran, 0};
249 break;
250 case Yaxis:
251 r0.max.y = n;
252 r1.min.y = n;
253 p0 = (Point){0, gran};
254 p1 = (Point){0, -gran};
255 break;
256 }
257
258 draw(tmp, im->r, im, display->black, im->r.min);
259 gendraw(im, r0, tmp, p0, mask, mask->r.min);
260 gendraw(im, r0, tmp, p1, mask, p1);
261 }
262
263
264 static void
265 writefile(char *name, Image *im, int gran)
266 {
267 static int c = 100;
268 int fd;
269 char buf[200];
270
271 snprint(buf, sizeof buf, "%d%s%d", c++, name, gran);
272 fd = create(buf, OWRITE, 0666);
273 if(fd < 0)
274 return;
275 writeimage(fd, im, 0);
276 close(fd);
277 }