plan9port

nrotate.c (5821B)

---

 /*
  * Rotate an image 180° in O(log Dx + log Dy)
  * draw calls, using an extra buffer the same size
  * as the image.
  *
  * The basic concept is that you can invert an array by
  * inverting the top half, inverting the bottom half, and
  * then swapping them.
  *
  * This is usually overkill, but it speeds up slow remote
  * connections quite a bit.
  */
 
 #include <u.h>
 #include <libc.h>
 #include <bio.h>
 #include <draw.h>
 #include <thread.h>
 #include <cursor.h>
 #include "page.h"
 
 int ndraw = 0;
 
 enum {
 	Xaxis,
 	Yaxis,
 };
 
 static void reverse(Image*, Image*, int);
 static void shuffle(Image*, Image*, int, int, Image*, int, int);
 static void writefile(char *name, Image *im, int gran);
 static void halvemaskdim(Image*);
 static void swapranges(Image*, Image*, int, int, int, int);
 
 /*
  * Rotate the image 180° by reflecting first
  * along the X axis, and then along the Y axis.
  */
 void
 rot180(Image *img)
 {
 	Image *tmp;
 
 	tmp = xallocimage(display, img->r, img->chan, 0, DNofill);
 	if(tmp == nil)
 		return;
 
 	reverse(img, tmp, Xaxis);
 	reverse(img, tmp, Yaxis);
 
 	freeimage(tmp);
 }
 
 Image *mtmp;
 
 static void
 reverse(Image *img, Image *tmp, int axis)
 {
 	Image *mask;
 	Rectangle r;
 	int i, d;
 
 	/*
 	 * We start by swapping large chunks at a time.
 	 * The chunk size should be the largest power of
 	 * two that fits in the dimension.
 	 */
 	d = axis==Xaxis ? Dx(img) : Dy(img);
 	for(i = 1; i*2 <= d; i *= 2)
 		;
 
 	r = axis==Xaxis ? Rect(0,0, i,100) : Rect(0,0, 100,i);
 	mask = xallocimage(display, r, GREY1, 1, DTransparent);
 	mtmp = xallocimage(display, r, GREY1, 1, DTransparent);
 
 	/*
 	 * Now color the bottom (or left) half of the mask opaque.
 	 */
 	if(axis==Xaxis)
 		r.max.x /= 2;
 	else
 		r.max.y /= 2;
 
 	draw(mask, r, display->opaque, nil, ZP);
 	writefile("mask", mask, i);
 
 	/*
 	 * Shuffle will recur, shuffling the pieces as necessary
 	 * and making the mask a finer and finer grating.
 	 */
 	shuffle(img, tmp, axis, d, mask, i, 0);
 
 	freeimage(mask);
 }
 
 /*
  * Shuffle the image by swapping pieces of size maskdim.
  */
 static void
 shuffle(Image *img, Image *tmp, int axis, int imgdim, Image *mask, int maskdim)
 {
 	int slop;
 
 	if(maskdim == 0)
 		return;
 
 	/*
 	 * Figure out how much will be left over that needs to be
 	 * shifted specially to the bottom.
 	 */
 	slop = imgdim % maskdim;
 
 	/*
 	 * Swap adjacent grating lines as per mask.
 	 */
 	swapadjacent(img, tmp, axis, imgdim - slop, mask, maskdim);
 
 	/*
 	 * Calculate the mask with gratings half as wide and recur.
 	 */
 	halvemaskdim(mask, maskdim, axis);
 	writefile("mask", mask, maskdim/2);
 
 	shuffle(img, tmp, axis, imgdim, mask, maskdim/2);
 
 	/*
 	 * Move the slop down to the bottom of the image.
 	 */
 	swapranges(img, tmp, 0, imgdim-slop, imgdim, axis);
 	moveup(im, tmp, lastnn, nn, n, axis);
 }
 
 /*
  * Halve the grating period in the mask.
  * The grating currently looks like
  * ####____####____####____####____
  * where #### is opacity.
  *
  * We want
  * ##__##__##__##__##__##__##__##__
  * which is achieved by shifting the mask
  * and drawing on itself through itself.
  * Draw doesn't actually allow this, so
  * we have to copy it first.
  *
  *     ####____####____####____####____ (dst)
  * +   ____####____####____####____#### (src)
  * in  __####____####____####____####__ (mask)
  * ===========================================
  *     ##__##__##__##__##__##__##__##__
  */
 static void
 halvemaskdim(Image *m, int maskdim, int axis)
 {
 	Point δ;
 
 	δ = axis==Xaxis ? Pt(maskdim,0) : Pt(0,maskdim);
 	draw(mtmp, mtmp->r, mask, nil, mask->r.min);
 	gendraw(mask, mask->r, mtmp, δ, mtmp, divpt(δ,2));
 	writefile("mask", mask, maskdim/2);
 }
 
 /*
  * Swap the regions [a,b] and [b,c]
  */
 static void
 swapranges(Image *img, Image *tmp, int a, int b, int c, int axis)
 {
 	Rectangle r;
 	Point δ;
 
 	if(a == b || b == c)
 		return;
 
 	writefile("swap", img, 0);
 	draw(tmp, tmp->r, im, nil, im->r.min);
 
 	/* [a,a+(c-b)] gets [b,c] */
 	r = img->r;
 	if(axis==Xaxis){
 		δ = Pt(1,0);
 		r.min.x = img->r.min.x + a;
 		r.max.x = img->r.min.x + a + (c-b);
 	}else{
 		δ = Pt(0,1);
 		r.min.y = img->r.min.y + a;
 		r.max.y = img->r.min.y + a + (c-b);
 	}
 	draw(img, r, tmp, nil, addpt(tmp->r.min, mulpt(δ, b)));
 
 	/* [a+(c-b), c] gets [a,b] */
 	r = img->r;
 	if(axis==Xaxis){
 		r.min.x = img->r.min.x + a + (c-b);
 		r.max.x = img->r.min.x + c;
 	}else{
 		r.min.y = img->r.min.y + a + (c-b);
 		r.max.y = img->r.min.y + c;
 	}
 	draw(img, r, tmp, nil, addpt(tmp->r.min, mulpt(δ, a)));
 	writefile("swap", img, 1);
 }
 
 /*
  * Swap adjacent regions as specified by the grating.
  * We do this by copying the image through the mask twice,
  * once aligned with the grading and once 180° out of phase.
  */
 static void
 swapadjacent(Image *img, Image *tmp, int axis, int imgdim, Image *mask, int maskdim)
 {
 	Point δ;
 	Rectangle r0, r1;
 
 	δ = axis==Xaxis ? Pt(1,0) : Pt(0,1);
 
 	r0 = img->r;
 	r1 = img->r;
 	switch(axis){
 	case Xaxis:
 		r0.max.x = imgdim;
 		r1.min.x = imgdim;
 		break;
 	case Yaxis:
 		r0.max.y = imgdim;
 		r1.min.y = imgdim;
 	}
 
 	/*
 	 * r0 is the lower rectangle, while r1 is the upper one.
 	 */
 	draw(tmp, tmp->r, img, nil,
 }
 
 void
 interlace(Image *im, Image *tmp, int axis, int n, Image *mask, int gran)
 {
 	Point p0, p1;
 	Rectangle r0, r1;
 
 	r0 = im->r;
 	r1 = im->r;
 	switch(axis) {
 	case Xaxis:
 		r0.max.x = n;
 		r1.min.x = n;
 		p0 = (Point){gran, 0};
 		p1 = (Point){-gran, 0};
 		break;
 	case Yaxis:
 		r0.max.y = n;
 		r1.min.y = n;
 		p0 = (Point){0, gran};
 		p1 = (Point){0, -gran};
 		break;
 	}
 
 	draw(tmp, im->r, im, display->black, im->r.min);
 	gendraw(im, r0, tmp, p0, mask, mask->r.min);
 	gendraw(im, r0, tmp, p1, mask, p1);
 }
 
 
 static void
 writefile(char *name, Image *im, int gran)
 {
 	static int c = 100;
 	int fd;
 	char buf[200];
 
 	snprint(buf, sizeof buf, "%d%s%d", c++, name, gran);
 	fd = create(buf, OWRITE, 0666);
 	if(fd < 0)
 		return;
 	writeimage(fd, im, 0);
 	close(fd);
 }