// cf. Steven Eker. Faster "Pixel-Perfect" Line Clipping. Graphics Gems V:
// 314-322.
// - Pixels are not missed at the ends of a clipped segment.
// - Visible pixels are the same as if there was no clipping.
private boolean clipLine(Rectangle r, final Line sl, Line dl) {
int code1 = 0, code2 = 0;
dl.x0 = sl.x0;
dl.y0 = sl.y0;
dl.x1 = sl.x1;
dl.y1 = sl.y1;
if (sl.x0 < r.xmin) code1 |= CLIP_LEFT;
if (sl.x0 > r.xmax) code1 |= CLIP_RIGHT;
if (sl.y0 < r.ymin) code1 |= CLIP_BOTTOM;
if (sl.y0 > r.ymax) code1 |= CLIP_TOP;
if (sl.x1 < r.xmin) code2 |= CLIP_LEFT;
if (sl.x1 > r.xmax) code2 |= CLIP_RIGHT;
if (sl.y1 < r.ymin) code2 |= CLIP_BOTTOM;
if (sl.y1 > r.ymax) code2 |= CLIP_TOP;
if ((code1 | code2) == 0) return false; // Trivial accept.
if ((code1 & code2) != 0) return true; // Trivial reject.
// Clip first end point.
if (code1 != 0) if (clipEndPoint(r, sl, dl, code1, false)) return true;
// Clip second end point.
if (code2 != 0) if (clipEndPoint(r, sl, dl, code2, true)) return true;
return false;
}
private boolean clipEndPoint(Rectangle r, final Line sl, Line dl, int code, boolean swap) {
// Rounding mode: 0=round toward 0, 1=round toward +infinity.
int x, y, dx, dy, sx = 1, sy = 1, roundX = 0, roundY = 0;
if (swap) {
x = sl.x1;
y = sl.y1;
dx = sl.x0 - sl.x1;
dy = sl.y0 - sl.y1;
} else {
x = sl.x0;
y = sl.y0;
dx = sl.x1 - sl.x0;
dy = sl.y1 - sl.y0;
}
if (dx < 0) {
dx = -dx;
sx = -1;
roundX ^= 1;
}
if (dy < 0) {
dy = -dy;
sy = -1;
roundY ^= 1;
}
int dx2 = dx << 1, dy2 = dy << 1, t0 = 0, t1 = 0;
int xc = x, yc = y;
if ((code & CLIP_LEFT) != 0) {
t0 = dy2 * (r.xmin - x);
xc = r.xmin;
}
if ((code & CLIP_RIGHT) != 0) {
t0 = dy2 * (x - r.xmax);
xc = r.xmax;
}
if ((code & CLIP_BOTTOM) != 0) {
t1 = dx2 * (r.ymin - y);
yc = r.ymin;
}
if ((code & CLIP_TOP) != 0) {
t1 = dx2 * (y - r.ymax);
yc = r.ymax;
}
if (CLIP_ZONE_FOR_CODE[code] == CLIP_ZONE_DIAGONALS) {
// Find which edge clips the line first and remove a clip flag.
if (dx >= dy) code &= ((t0 - t1 + dx - (roundX ^ 1)) < 0) ? ~CLIP_HORIZONTAL : ~CLIP_VERTICAL;
else code &= ((t1 - t0 + dy - (roundY ^ 1)) < 0) ? ~CLIP_VERTICAL : ~CLIP_HORIZONTAL;
}
if ((code & CLIP_HORIZONTAL) != 0) {
// Clip to left or right edge.
t0 = (dx >= dy) ? (t0 + dx - (roundX ^ 1)) / dx2 : (t0 - dy + dx2 - roundY) / dx2;
yc = (sy < 0) ? (y - t0) : (y + t0);
if ((yc < r.ymin) || (yc > r.ymax)) return true;
} else {
// Clip to bottom or top edge.
t1 = (dx >= dy) ? (t1 - dx + dy2 - roundX) / dy2 : (t1 + dy - (roundY ^ 1)) / dy2;
xc = (sx < 0) ? (x - t1) : (x + t1);
if ((xc < r.xmin) || (xc > r.xmax)) return true;
}
if (swap) {
dl.x1 = xc;
dl.y1 = yc;
} else {
dl.x0 = xc;
dl.y0 = yc;
}
return false;
}
private void drawLine(int x0, int y0, int x1, int y1, boolean lastPixelFlag) {
if (y0 == y1) {
drawHLine(x0, x1, y0);
return;
}
if (x0 == x1) {
drawVLine(y0, y1, x0);
return;
}
// Clip.
Line sl = srcLine, dl = dstLine;
// sl.x0=x0-translationX; sl.x1=x1-translationX; sl.y0=y0-translationY;
// sl.y1=y1-translationY;
sl.x0 = x0 + transX;
sl.x1 = x1 + transX;
sl.y0 = y0 + transY;
sl.y1 = y1 + transY;
if (clipLine(clipRectangle, sl, dl)) return;
// Draw.
{
int x = dl.x0, y = dl.y0, w = dl.x1 - dl.x0, h = dl.y1 - dl.y0;
int ex = dl.x0 - sl.x0, ey = dl.y0 - sl.y0;
int dx = sl.x1 - sl.x0, dy = sl.y1 - sl.y0;
int sx = 1, sy = 1;
if (dx < 0) {
dx = -dx;
sx = -sx;
ex = -ex;
w = -w;
}
if (dy < 0) {
dy = -dy;
sy = -sy;
ey = -ey;
h = -h;
}
if (dx >= dy) {
int decision = (ex + ex + 2) * dy - (ey + ey + 1) * dx;
if (sx > 0) decision--; // Modify the decision variable for generating
// the same pattern from left to right and right
// to left.
dx += dx;
dy += dy;
if (lastPixelFlag) w++;
while (w > 0) {
drawSpan(x, y, 1);
if (decision >= 0) {
decision -= dx;
y += sy;
}
decision += dy;
x += sx;
w--;
}
} else {
int decision = (ey + ey + 2) * dx - (ex + ex + 1) * dy;
if (sy > 0) decision--; // Modify the decision variable for generating
// the same pattern from bottom to top and top
// to bottom.
dx += dx;
dy += dy;
if (lastPixelFlag) h++;
while (h > 0) {
drawSpan(x, y, 1);
if (decision >= 0) {
decision -= dy;
x += sx;
}
decision += dx;
y += sy;
h--;
}
}
}
}
