Integrate the line drawing algorithm from the book "Graphic Gems 1".
http://www.graphicsgems.org/ At the time it claimed to be 3-4 times faster than the traditional algorithm. PR: 18769 Approved by: jhb (mentor) MFC after: 2 weeks
This commit is contained in:
Pedro F. Giffuni
parent
9f745f61b8
commit
4c995944af
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=229415
@ -198,36 +198,205 @@ VGLGetXY(VGLBitmap *object, int x, int y)
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return 0; /* XXX black? */
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}
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/*
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* Symmetric Double Step Line Algorithm by Brian Wyvill from
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* "Graphics Gems", Academic Press, 1990.
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*/
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#define SL_SWAP(a,b) {a^=b; b^=a; a^=b;}
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#define SL_ABSOLUTE(i,j,k) ( (i-j)*(k = ( (i-j)<0 ? -1 : 1)))
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void
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plot(VGLBitmap * object, int x, int y, int flag, byte color)
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{
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/* non-zero flag indicates the pixels need swapping back. */
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if (flag)
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VGLSetXY(object, y, x, color);
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else
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VGLSetXY(object, x, y, color);
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}
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void
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VGLLine(VGLBitmap *object, int x1, int y1, int x2, int y2, u_long color)
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{
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int d, x, y, ax, ay, sx, sy, dx, dy;
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int dx, dy, incr1, incr2, D, x, y, xend, c, pixels_left;
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int sign_x, sign_y, step, reverse, i;
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dx = x2-x1; ax = ABS(dx)<<1; sx = SGN(dx); x = x1;
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dy = y2-y1; ay = ABS(dy)<<1; sy = SGN(dy); y = y1;
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dx = SL_ABSOLUTE(x2, x1, sign_x);
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dy = SL_ABSOLUTE(y2, y1, sign_y);
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/* decide increment sign by the slope sign */
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if (sign_x == sign_y)
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step = 1;
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else
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step = -1;
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if (ax>ay) { /* x dominant */
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d = ay-(ax>>1);
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for (;;) {
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VGLSetXY(object, x, y, color);
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if (x==x2)
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break;
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if (d>=0) {
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y += sy; d -= ax;
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}
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x += sx; d += ay;
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}
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if (dy > dx) { /* chooses axis of greatest movement (make dx) */
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SL_SWAP(x1, y1);
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SL_SWAP(x2, y2);
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SL_SWAP(dx, dy);
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reverse = 1;
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} else
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reverse = 0;
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/* note error check for dx==0 should be included here */
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if (x1 > x2) { /* start from the smaller coordinate */
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x = x2;
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y = y2;
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x1 = x1;
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y1 = y1;
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} else {
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x = x1;
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y = y1;
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x1 = x2;
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y1 = y2;
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}
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else { /* y dominant */
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d = ax-(ay>>1);
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for (;;) {
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VGLSetXY(object, x, y, color);
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if (y==y2)
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break;
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if (d>=0) {
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x += sx; d -= ay;
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/* Note dx=n implies 0 - n or (dx+1) pixels to be set */
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/* Go round loop dx/4 times then plot last 0,1,2 or 3 pixels */
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/* In fact (dx-1)/4 as 2 pixels are already plotted */
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xend = (dx - 1) / 4;
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pixels_left = (dx - 1) % 4; /* number of pixels left over at the
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* end */
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plot(object, x, y, reverse, color);
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if (pixels_left < 0)
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return; /* plot only one pixel for zero length
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* vectors */
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plot(object, x1, y1, reverse, color); /* plot first two points */
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incr2 = 4 * dy - 2 * dx;
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if (incr2 < 0) { /* slope less than 1/2 */
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c = 2 * dy;
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incr1 = 2 * c;
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D = incr1 - dx;
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for (i = 0; i < xend; i++) { /* plotting loop */
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++x;
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--x1;
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if (D < 0) {
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/* pattern 1 forwards */
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plot(object, x, y, reverse, color);
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plot(object, ++x, y, reverse, color);
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/* pattern 1 backwards */
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plot(object, x1, y1, reverse, color);
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plot(object, --x1, y1, reverse, color);
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D += incr1;
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} else {
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if (D < c) {
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/* pattern 2 forwards */
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plot(object, x, y, reverse, color);
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plot(object, ++x, y += step, reverse,
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color);
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/* pattern 2 backwards */
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plot(object, x1, y1, reverse, color);
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plot(object, --x1, y1 -= step, reverse,
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color);
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} else {
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/* pattern 3 forwards */
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plot(object, x, y += step, reverse, color);
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plot(object, ++x, y, reverse, color);
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/* pattern 3 backwards */
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plot(object, x1, y1 -= step, reverse,
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color);
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plot(object, --x1, y1, reverse, color);
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}
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D += incr2;
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}
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} /* end for */
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/* plot last pattern */
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if (pixels_left) {
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if (D < 0) {
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plot(object, ++x, y, reverse, color); /* pattern 1 */
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if (pixels_left > 1)
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plot(object, ++x, y, reverse, color);
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if (pixels_left > 2)
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plot(object, --x1, y1, reverse, color);
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} else {
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if (D < c) {
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plot(object, ++x, y, reverse, color); /* pattern 2 */
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if (pixels_left > 1)
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plot(object, ++x, y += step, reverse, color);
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if (pixels_left > 2)
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plot(object, --x1, y1, reverse, color);
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} else {
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/* pattern 3 */
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plot(object, ++x, y += step, reverse, color);
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if (pixels_left > 1)
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plot(object, ++x, y, reverse, color);
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if (pixels_left > 2)
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plot(object, --x1, y1 -= step, reverse, color);
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}
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}
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} /* end if pixels_left */
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}
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/* end slope < 1/2 */
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else { /* slope greater than 1/2 */
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c = 2 * (dy - dx);
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incr1 = 2 * c;
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D = incr1 + dx;
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for (i = 0; i < xend; i++) {
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++x;
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--x1;
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if (D > 0) {
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/* pattern 4 forwards */
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plot(object, x, y += step, reverse, color);
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plot(object, ++x, y += step, reverse, color);
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/* pattern 4 backwards */
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plot(object, x1, y1 -= step, reverse, color);
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plot(object, --x1, y1 -= step, reverse, color);
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D += incr1;
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} else {
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if (D < c) {
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/* pattern 2 forwards */
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plot(object, x, y, reverse, color);
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plot(object, ++x, y += step, reverse,
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color);
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/* pattern 2 backwards */
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plot(object, x1, y1, reverse, color);
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plot(object, --x1, y1 -= step, reverse,
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color);
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} else {
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/* pattern 3 forwards */
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plot(object, x, y += step, reverse, color);
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plot(object, ++x, y, reverse, color);
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/* pattern 3 backwards */
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plot(object, x1, y1 -= step, reverse, color);
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plot(object, --x1, y1, reverse, color);
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}
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D += incr2;
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}
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} /* end for */
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/* plot last pattern */
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if (pixels_left) {
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if (D > 0) {
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plot(object, ++x, y += step, reverse, color); /* pattern 4 */
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if (pixels_left > 1)
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plot(object, ++x, y += step, reverse,
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color);
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if (pixels_left > 2)
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plot(object, --x1, y1 -= step, reverse,
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color);
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} else {
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if (D < c) {
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plot(object, ++x, y, reverse, color); /* pattern 2 */
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if (pixels_left > 1)
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plot(object, ++x, y += step, reverse, color);
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if (pixels_left > 2)
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plot(object, --x1, y1, reverse, color);
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} else {
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/* pattern 3 */
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plot(object, ++x, y += step, reverse, color);
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if (pixels_left > 1)
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plot(object, ++x, y, reverse, color);
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if (pixels_left > 2) {
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if (D > c) /* step 3 */
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plot(object, --x1, y1 -= step, reverse, color);
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else /* step 2 */
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plot(object, --x1, y1, reverse, color);
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}
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}
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}
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y += sy; d += ax;
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}
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}
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}
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