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 <event.h>
19 #include "page.h"
20
21 int ndraw = 0;
22
23 enum {
24 Xaxis,
25 Yaxis,
26 };
27
28 static void reverse(Image*, Image*, int);
29 static void shuffle(Image*, Image*, int, int, Image*, int, int);
30 static void writefile(char *name, Image *im, int gran);
31 static void halvemaskdim(Image*);
32 static void swapranges(Image*, Image*, int, int, int, int);
33
34 /*
35 * Rotate the image 180° by reflecting first
36 * along the X axis, and then along the Y axis.
37 */
38 void
rot180(Image * img)39 rot180(Image *img)
40 {
41 Image *tmp;
42
43 tmp = xallocimage(display, img->r, img->chan, 0, DNofill);
44 if(tmp == nil)
45 return;
46
47 reverse(img, tmp, Xaxis);
48 reverse(img, tmp, Yaxis);
49
50 freeimage(tmp);
51 }
52
53 Image *mtmp;
54
55 static void
reverse(Image * img,Image * tmp,int axis)56 reverse(Image *img, Image *tmp, int axis)
57 {
58 Image *mask;
59 Rectangle r;
60 int i, d;
61
62 /*
63 * We start by swapping large chunks at a time.
64 * The chunk size should be the largest power of
65 * two that fits in the dimension.
66 */
67 d = axis==Xaxis ? Dx(img) : Dy(img);
68 for(i = 1; i*2 <= d; i *= 2)
69 ;
70
71 r = axis==Xaxis ? Rect(0,0, i,100) : Rect(0,0, 100,i);
72 mask = xallocimage(display, r, GREY1, 1, DTransparent);
73 mtmp = xallocimage(display, r, GREY1, 1, DTransparent);
74
75 /*
76 * Now color the bottom (or left) half of the mask opaque.
77 */
78 if(axis==Xaxis)
79 r.max.x /= 2;
80 else
81 r.max.y /= 2;
82
83 draw(mask, r, display->opaque, nil, ZP);
84 writefile("mask", mask, i);
85
86 /*
87 * Shuffle will recur, shuffling the pieces as necessary
88 * and making the mask a finer and finer grating.
89 */
90 shuffle(img, tmp, axis, d, mask, i, 0);
91
92 freeimage(mask);
93 }
94
95 /*
96 * Shuffle the image by swapping pieces of size maskdim.
97 */
98 static void
shuffle(Image * img,Image * tmp,int axis,int imgdim,Image * mask,int maskdim)99 shuffle(Image *img, Image *tmp, int axis, int imgdim, Image *mask, int maskdim)
100 {
101 int slop;
102
103 if(maskdim == 0)
104 return;
105
106 /*
107 * Figure out how much will be left over that needs to be
108 * shifted specially to the bottom.
109 */
110 slop = imgdim % maskdim;
111
112 /*
113 * Swap adjacent grating lines as per mask.
114 */
115 swapadjacent(img, tmp, axis, imgdim - slop, mask, maskdim);
116
117 /*
118 * Calculate the mask with gratings half as wide and recur.
119 */
120 halvemaskdim(mask, maskdim, axis);
121 writefile("mask", mask, maskdim/2);
122
123 shuffle(img, tmp, axis, imgdim, mask, maskdim/2);
124
125 /*
126 * Move the slop down to the bottom of the image.
127 */
128 swapranges(img, tmp, 0, imgdim-slop, imgdim, axis);
129 moveup(im, tmp, lastnn, nn, n, axis);
130 }
131
132 /*
133 * Halve the grating period in the mask.
134 * The grating currently looks like
135 * ####____####____####____####____
136 * where #### is opacity.
137 *
138 * We want
139 * ##__##__##__##__##__##__##__##__
140 * which is achieved by shifting the mask
141 * and drawing on itself through itself.
142 * Draw doesn't actually allow this, so
143 * we have to copy it first.
144 *
145 * ####____####____####____####____ (dst)
146 * + ____####____####____####____#### (src)
147 * in __####____####____####____####__ (mask)
148 * ===========================================
149 * ##__##__##__##__##__##__##__##__
150 */
151 static void
halvemaskdim(Image * m,int maskdim,int axis)152 halvemaskdim(Image *m, int maskdim, int axis)
153 {
154 Point δ;
155
156 δ = axis==Xaxis ? Pt(maskdim,0) : Pt(0,maskdim);
157 draw(mtmp, mtmp->r, mask, nil, mask->r.min);
158 gendraw(mask, mask->r, mtmp, δ, mtmp, divpt(δ,2));
159 writefile("mask", mask, maskdim/2);
160 }
161
162 /*
163 * Swap the regions [a,b] and [b,c]
164 */
165 static void
swapranges(Image * img,Image * tmp,int a,int b,int c,int axis)166 swapranges(Image *img, Image *tmp, int a, int b, int c, int axis)
167 {
168 Rectangle r;
169 Point δ;
170
171 if(a == b || b == c)
172 return;
173
174 writefile("swap", img, 0);
175 draw(tmp, tmp->r, im, nil, im->r.min);
176
177 /* [a,a+(c-b)] gets [b,c] */
178 r = img->r;
179 if(axis==Xaxis){
180 δ = Pt(1,0);
181 r.min.x = img->r.min.x + a;
182 r.max.x = img->r.min.x + a + (c-b);
183 }else{
184 δ = Pt(0,1);
185 r.min.y = img->r.min.y + a;
186 r.max.y = img->r.min.y + a + (c-b);
187 }
188 draw(img, r, tmp, nil, addpt(tmp->r.min, mulpt(δ, b)));
189
190 /* [a+(c-b), c] gets [a,b] */
191 r = img->r;
192 if(axis==Xaxis){
193 r.min.x = img->r.min.x + a + (c-b);
194 r.max.x = img->r.min.x + c;
195 }else{
196 r.min.y = img->r.min.y + a + (c-b);
197 r.max.y = img->r.min.y + c;
198 }
199 draw(img, r, tmp, nil, addpt(tmp->r.min, mulpt(δ, a)));
200 writefile("swap", img, 1);
201 }
202
203 /*
204 * Swap adjacent regions as specified by the grating.
205 * We do this by copying the image through the mask twice,
206 * once aligned with the grading and once 180° out of phase.
207 */
208 static void
swapadjacent(Image * img,Image * tmp,int axis,int imgdim,Image * mask,int maskdim)209 swapadjacent(Image *img, Image *tmp, int axis, int imgdim, Image *mask, int maskdim)
210 {
211 Point δ;
212 Rectangle r0, r1;
213
214 δ = axis==Xaxis ? Pt(1,0) : Pt(0,1);
215
216 r0 = img->r;
217 r1 = img->r;
218 switch(axis){
219 case Xaxis:
220 r0.max.x = imgdim;
221 r1.min.x = imgdim;
222 break;
223 case Yaxis:
224 r0.max.y = imgdim;
225 r1.min.y = imgdim;
226 }
227
228 /*
229 * r0 is the lower rectangle, while r1 is the upper one.
230 */
231 draw(tmp, tmp->r, img, nil,
232 }
233
234 void
235 interlace(Image *im, Image *tmp, int axis, int n, Image *mask, int gran)
236 {
237 Point p0, p1;
238 Rectangle r0, r1;
239
240 r0 = im->r;
241 r1 = im->r;
242 switch(axis) {
243 case Xaxis:
244 r0.max.x = n;
245 r1.min.x = n;
246 p0 = (Point){gran, 0};
247 p1 = (Point){-gran, 0};
248 break;
249 case Yaxis:
250 r0.max.y = n;
251 r1.min.y = n;
252 p0 = (Point){0, gran};
253 p1 = (Point){0, -gran};
254 break;
255 }
256
257 draw(tmp, im->r, im, display->black, im->r.min);
258 gendraw(im, r0, tmp, p0, mask, mask->r.min);
259 gendraw(im, r0, tmp, p1, mask, p1);
260 }
261
262
263 static void
264 writefile(char *name, Image *im, int gran)
265 {
266 static int c = 100;
267 int fd;
268 char buf[200];
269
270 snprint(buf, sizeof buf, "%d%s%d", c++, name, gran);
271 fd = create(buf, OWRITE, 0666);
272 if(fd < 0)
273 return;
274 writeimage(fd, im, 0);
275 close(fd);
276 }
277
278